View source for Timeline of Solar System astronomy

{{short description|none}} <!-- "none" is preferred when the title is sufficiently descriptive; see [[WP:SDNONE]] -->
The following is a [[timeline]] of [[Solar System]] [[astronomy]] and [[science]]. It includes the advances in the knowledge of the [[Earth]] at [[Planetary science|planetary scale]], as part of it.
[[File:Venustransit 2004-06-08 07-49.jpg|thumb|200 px|upright|A [[transit of Venus]]]]

==Direct observation==

[[Human]]s (''Homo sapiens'') have inhabited the [[Earth]] in the last 300,000 years at least,<ref>{{cite journal |last1=Hublin |first1=Jean-Jacques |last2=Ben-Ncer |first2=Abdelouahed |last3=Bailey |first3=Shara E. |last4=Freidline |first4=Sarah E. |last5=Neubauer |first5=Simon |last6=Skinner |first6=Matthew M. |last7=Bergmann |first7=Inga |last8=Le Cabec |first8=Adeline |last9=Benazzi |first9=Stefano |last10=Harvati |first10=Katerina |last11=Gunz |first11=Philipp |title=New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens |journal=Nature |date=8 June 2017 |volume=546 |issue=7657 |pages=289–292 |doi=10.1038/nature22336 |bibcode=2017Natur.546..289H |pmid=28593953 |hdl=11585/610328 |url=https://kar.kent.ac.uk/62267/1/Submission_288356_1_art_file_2637492_j96j1b.pdf |hdl-access=free }}</ref> and they had witnessed directly observable [[Astronomy|astronomical]] and [[Geology|geological]] phenomena. For millennia, these have arose admiration and curiosity, being admitted as of [[wikt:superhuman|superhuman]] nature and scale. Multiple imaginative interpretations were being fixed in [[oral tradition]]s of difficult dating, and incorporated into a variety of [[Belief#Belief systems|belief system]]s, as [[animism]], [[shamanism]], [[mythology]], [[religion]] and/or [[philosophy]].

Although such phenomena are not "[[Discovery (observation)|discoveries]]" ''per se'', as they are part of the common human experience, their observation shape the knowledge and comprehension of the world around us, and about its position in the [[observable universe]], in which the [[Sun]] plays a role of outmost importance for us. What today is known to be the  [[Solar System]] was regarded for generations as the contents of the "whole [[universe]]".

The most relevant phenomena of these kind are:

* Basic [[gravity]]. Following the [[trajectory]] of free falling objects, the [[Earth]] is "below" us and the [[sky]] is "above" us.
* Characterization of the [[Earth#Surface|terrestrial surface]], in four main types of [[terrain]]: lands covered with [[vegetation]]; dry [[desert]]s; bodies of liquid [[water]], both salted ([[sea]]s and [[ocean]]s) and fresh ([[river]]s and [[lake]]s); and frozen landscapes ([[glaciar]]s, [[polar ice cap]]s). Recognition of emerged lands and [[Underwater|submerged]] ones. Recognition of [[mountain range]]s and cavities ([[grotto]]s and [[cavern]]s).
* Characterization of the Earth's [[atmosphere]] and its associated [[Meteorology|meteorological]] phenomena: [[cloud]]s, [[rain]], [[hail]] and [[snow]]; [[wind]], [[storms]] and [[thunderstorm]]s, [[tornado]]es and [[Hurricane|hurricanes/cyclones/typhoon]]s; [[Flood|fluvial flood]]s, [[Deluge (prehistoric)|deluge]]s, [[landslide]]s and [[avalanche]]s; [[rainbow]]s and [[Halo (optical phenomenon)|halo]]s; [[mirage]]s; [[glacial age]]s.
* [[Day|Diurnal]] apparent movement of the Sun: [[sunrise]], [[noon]] and [[sunset]]. Recognition of the four [[cardinal point]]s: [[north]], [[south]], [[east]], and [[west]].
* [[Night]]ly apparent movement of the [[celestial sphere]] with its main features regarded as "[[Fixed stars|fixed]]": [[star]]s, the brightest of them forming casual groupings known as [[constellation]]s, under different names and shapes in many cultures. Different constellations are viewed in different seasons and [[latitude]]s. Along with the faint strip of the [[Milky Way]], they altogether conform the idea of the [[firmament]], which as viewed from Earth it seems to be a consistent, solid unit rotating smooth and uniformly. This leads to the intuitive idea of a [[geocentric universe]].
* Presence of the [[Moon]], with its [[Phases of the Moon|phase]]s. [[Tide]]s. Recognition of meteorological phenomena as sub-lunar.
* [[Year]]ly apparent transit of the Sun through the constellations of the [[zodiac]]. Recognition of the lunar cycle as a (lunar) [[month]], and the solar cycle as the (solar) year, the basis for [[calendar]]s.
* Observation of non-fixed or "wandering" objects in the [[night sky]]: the five [[classical planet]]s; [[shooting star]]s and [[meteor shower]]s; [[bolide]]s; [[comet]]s; [[aurora]]s; [[zodiacal light]].
* [[Solar eclipse|Solar]] and [[lunar eclipse]]s. [[Planetary conjunction]]s.
* Identification of the [[Geographical zone|frigid, temperate and torrid zone]]s of the Earth by latitude. [[Equator]] and [[Tropic]]s. Four [[season]]s in temperate zones: [[Spring (season)|spring]], [[summer]], [[autumn]] and [[winter]]. [[Equinox]]es and [[solstice]]s. [[Monsoon]]s. [[Midnight sun]].
* Telluric phenomena: [[seismic]] ([[earthquake]]s and [[seaquake]]s; [[tsunami]]s). [[Geyser]]s. [[Volcano]]es.

Along with an indeterminate number of unregistered sightings of rare events: [[meteor impact]]s; [[novae]] and [[supernovae]].

==Antiquity==
{{See also|Timeline of Chinese astronomy}}
[[File:Venus_Tablet_of_Ammisaduqa.jpg|thumb|175px|right|[[Venus tablet of Ammisaduqa]]]]
{{Use dmy dates|date=April 2015}}
{{multiple image
| direction = vertical
| width     = 175
| image1    = Antikythera Fragment A (Front).webp
| caption1  = The [[Antikythera mechanism]] (Fragment A&nbsp;– front); visible is the largest gear in the mechanism, approximately {{convert|140|mm|in}} in diameter
| image2    = Antikythera Fragment A (Back).webp
| caption2  = The Antikythera mechanism (Fragment A&nbsp;– back)
}}

* '''2nd millennium BCE'''&nbsp;– Earliest possible date for the composition of the Babylonian [[Venus tablet of Ammisaduqa]], a 7th-century BC copy<ref>{{cite thesis |first=Russell |last=Hobson |title=The Exact Transmission of Texts in the First Millennium B.C. |type=PhD thesis |publisher=[[University of Sydney]] |date=2009 |url=http://ses.library.usyd.edu.au/bitstream/2123/5404/1/r-hobson-2009-thesis.pdf}}</ref> of a list of observations of the motions of the planet [[Venus]], and the oldest planetary table currently known.
* '''2nd millennium BCE'''&nbsp;– [[Babylonian astronomy|Babylonian astronomers]] identify the inner planets [[Mercury (planet)|Mercury]] and Venus and the outer planets [[Mars]], [[Jupiter]] and [[Saturn]], which would remain the only known planets until the invention of the [[telescope]] in early modern times.<ref>{{cite journal |title=Babylonian observational astronomy |journal=Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences |date=2 May 1974 |volume=276 |issue=1257 |pages=43–50 |doi=10.1098/rsta.1974.0008 |jstor=74273 |bibcode=1974RSPTA.276...43S |last1=Sachs |first1=A. }}</ref>
* '''Late 2nd millennium BCE'''&nbsp;– [[Chinese astronomy|Chinese astronomers]] record a [[solar eclipse]] during the reign of [[Zhong Kang]], described as part of the document ''Punitive Expedition of Yin'' in the ''[[Book of Documents]]''.<ref>{{cite web |url=https://ctext.org/shang-shu/punitive-expedition-of-yin |title=Punitive expedition of Yin| website=ctext |quote=On the first day of the last month of autumn, the sun and moon did not meet harmoniously in Fang}}</ref>
* '''Late 2nd millennium BCE'''&nbsp;– Chinese established their timing cycle of 12 [[Earthly Branches]] based on the approximate number of years (11.86) it takes [[Jupiter]] to complete a single revolution in the sky.{{citation needed|date=February 2019}}
* {{circa}} '''1200 BCE'''&nbsp;– Earliest [[Mesopotamian astronomy|Babylonian]] [[Babylonian star catalogues|star catalogues]].<ref>{{cite journal |last1=Rogers |first1=J. H. |title=Origins of the ancient constellations: I. The Mesopotamian traditions |journal=Journal of the British Astronomical Association |date=February 1998 |volume=108 |pages=9–28 |bibcode=1998JBAA..108....9R |bibcode-access=free }}</ref>
* {{circa}} '''1100 BCE'''&nbsp;– Chinese first determine the [[spring equinox (Northern Hemisphere)|spring equinox]]. {{citation needed|date=November 2022}}
* {{circa}} '''750 BCE'''&nbsp;– During the reign of [[Nabonassar]] (747–733 BC), the systematic records of ominous phenomena in [[Babylonian astronomical diaries]] that began at this time allowed for the discovery of a repeating 18-year cycle of [[lunar eclipse]]s.<ref>{{Cite journal|title=Saros Cycle Dates and Related Babylonian Astronomical Texts|author=A. Aaboe |author2=J. P. Britton |author3=J. A. Henderson |author4=[[Otto Neugebauer]] |author5=A. J. Sachs|journal=Transactions of the American Philosophical Society|volume=81|issue=6|year=1991|pages=1–75|publisher=[[American Philosophical Society]]|quote=One comprises what we have called "Saros Cycle Texts," which give the months of eclipse possibilities arranged in consistent cycles of 223 months (or 18 years).|jstor=1006543|doi=10.2307/1006543}}</ref>
* '''776 BCE'''&nbsp;– Chinese make the earliest reliable record of a solar eclipse.<ref>{{cite journal |author=Stephenson, F. Richard |date=1982 |title=Historical Eclipses |journal=Scientific American|volume=247|issue=4|pages=154–163|doi=10.1038/scientificamerican1082-170 |bibcode=1982SciAm.247d.154S }}</ref>{{failed verification | date=October 2023 }}
* '''687 BCE'''&nbsp;– Chinese make earliest known record of [[meteor shower]].<ref>{{Cite web |title=Lyrids – NASA Science |url=https://science.nasa.gov/solar-system/meteors-meteorites/lyrids/ |access-date=2024-01-22 |website=science.nasa.gov |date=20 November 2017 |language=en}}</ref>
* '''7th century BCE'''&nbsp;– [[Egyptian astronomy|Egyptian astronomers]] alleged to have predicted a solar eclipse. {{citation needed|date=November 2022}}
* '''613 BCE'''&nbsp;– A [[comet]], possibly [[Comet Halley]], is recorded in ''[[Spring and Autumn Annals]]'' by the Chinese.<ref>{{cite book |first=Endymion |last=Wilkinson |title=Chinese History: A New Manual |year=2012 |publisher=Harvard-Yenching Institute; Harvard University Asia Center |series=Harvard-Yenching Institute Monograph Series '''84''' | pages=612 |isbn=978-0-674-06715-8}}</ref>
* '''586 BCE'''&nbsp;– [[Thales of Miletus]] alleged to have [[Eclipse of Thales|predicted]] a solar eclipse.<ref>{{cite journal |last1=Stephenson |first1=F. Richard |last2=Fatoohi |first2=Louay J. |title=Thales's Prediction of a Solar Eclipse |journal=Journal for the History of Astronomy |date=November 1997 |volume=28 |issue=4 |pages=279–282 |doi=10.1177/002182869702800401 |bibcode=1997JHA....28..279S |bibcode-access=free }}</ref>
* {{circa}} '''560 BCE'''&nbsp;– [[Anaximander]] posits a mechanical model of the world: a [[Cylinder|cylindrical]] Earth<ref>"A column of stone", [[Aëtius (theologian)|Aetius]] reports in ''De Fide'' (III, 7, 1), or "similar to a pillar-shaped stone", pseudo-Plutarch (III, 10).</ref> floats freely in space surrounded by three concentric wheels turning at different distances: the closest for the stars and planets, the second for the Moon and the farthest for the Sun, all conceived not as bodies but as "fire seen thru holes" in every wheel.<ref>Most of Anaximander's model of the Universe comes from pseudo-Plutarch (II, 20–28):
: "[The Sun] is a circle twenty-eight times as big as the Earth, with the outline similar to that of a fire-filled chariot wheel, on which appears a mouth in certain places and through which it exposes its fire, as through the hole on a flute. [...] the Sun is equal to the Earth, but the circle on which it breathes and on which it's borne is twenty-seven times as big as the whole earth. [...] [The eclipse] is when the mouth from which comes the fire heat is closed. [...] [The Moon] is a circle nineteen times as big as the whole earth, all filled with fire, like that of the Sun".</ref> But he starts to feed the idea of [[celestial mechanics]] as different of the notion of planets being heavenly [[deity|deities]], leaving [[Greek mythology|mythology]] aside.
* {{circa}} '''475 BCE'''&nbsp;– [[Parmenides]] is credited to be the first Greek who declared that the Earth is spherical and is situated in the centre of the universe, believed to have been the first to detect the identity of [[Hesperus]], the evening-star, and [[Phosphorus (morning star)|Phosphorus]], the morning-star (Venus), and by some, the first to claim that moonlight is a reflection of sunlight.<ref>{{cite book|title=Early astronomy|last=Thurston|first=Hugh|publisher=Springer-Verlag New York|year=1994|isbn=0-387-94107-X|location=New York|page=110}}</ref>
* {{circa}} '''450 BCE'''&nbsp;– [[Anaxagoras]] shows that the [[Moon]] shines by reflected sunlight: the phases of the Moon are caused by the illumination of its sphere by the Sun in different angles along the lunar month. He was also the first to give a correct explanation of eclipses, by asserting that the Moon is [[Rock (geology)|rocky]], thus [[Opacity (optics)|opaque]], and closer to the Earth than the Sun.<ref>{{cite SEP |url-id=anaxagoras |title=Anaxagoras |last=Curd |first=Patricia | date=2019}}</ref>
* {{circa}} '''400 BCE'''&nbsp;– [[Philolaus]] and other [[Pythagoreanism|Pythagoreans]] propose [[Pythagorean astronomical system|a model]] in which the Earth and the Sun revolve around an invisible "Central Fire" (not the Sun), and the Moon and the planets orbit the Earth.<ref>{{Cite book|title=Early astronomy|last=Thurston|first=Hugh|publisher=Springer-Verlag New York|year=1994|isbn=0-387-94107-X|location=New York|page=111}}</ref> Due to philosophical concerns [[Tetractys|about the number 10]], they also added a tenth "hidden body" or [[Counter-Earth]] (''Antichthon''), always in the opposite side of the invisible Central Fire and therefore also invisible from Earth.<ref name=Dreyer>{{cite book|last=Dreyer|first=John Louis Emil|title=History of the planetary systems from Thales to Kepler|year=1906|page=42|quote=To complete the number ten, Philolaus created the antichthon, or counter-earth. This tenth planet is always invisible to us, because it is between us and the central fire and always keeps pace with the Earth.|url=https://books.google.com/books?id=OgRAAQAAIAAJ&q=counter-earth+Antichthon+mysterious&pg=PA42}}</ref>
* {{circa}} '''360 BCE'''&nbsp;– [[Plato]] claims in his ''[[Timaeus (dialogue)|Timaeus]]'' that [[Celestial spheres|circles and spheres]] are the preferred shape of the universe and that the Earth is at the centre. These circles are the orbits of the heavenly bodies, varying in size for every of them. He arranged these celestial orbs, in increasing order from the Earth: Moon, Sun, Venus, Mercury, Mars, Jupiter, Saturn, and the [[fixed stars]] located on the [[celestial sphere]] forming the outermost shell.<ref>{{Cite book|title=Early physics and astronomy. A historical introduction|last=Pedersen|first=Olaf|publisher=Cambridge University Press|year=1993|isbn=0-521-40340-5|location=Cambridge (UK)}}</ref>
* {{circa}} '''360 BCE'''&nbsp;– [[Eudoxus of Cnidus]] proposes for first time a purely [[Geometry|geometric-mathematical]], [[Geocentrism|geocentric]] [[Concentric spheres|model of the planetary movements]], including that of the Sun and the Moon.<ref>"Eudoxus of Cnidus." Complete Dictionary of Scientific Biography. Vol. 4. Detroit: Charles Scribner's Sons, 2008. 465–467. Gale Virtual Reference Library. Web. 2 June 2014.</ref>
* {{circa}} '''350 BCE'''&nbsp;– [[Aristotle]] argues for a spherical Earth using [[lunar eclipse]]s<ref>''De caelo'', 297b31–298a10</ref> and other observations. Also, he asserts his conception of the [[Celestial spheres|heavenly spheres]],<ref>Grant, ''Planets, Stars, and Orbs'', p. 440.</ref> and of an [[outer space]] fulfilled with [[Aether (classical element)|aether]].<ref>{{ cite book |author=Lloyd, G. E. R.|date=1968|title=The critic of Plato. Aristotle: The Growth and Structure of His Thought|publisher=Cambridge University Press| isbn=978-0-521-09456-6 }}</ref>
* {{circa}} '''330 BCE'''&nbsp;– [[Heraclides Ponticus]] is said to be the first Greek who proposes that the [[rotation of the Earth|Earth rotates]] on its axis, from west to east, once every 24 hours, contradicting Aristotle's teachings. [[Simplicius of Cilicia|Simplicius]] says that Heraclides proposed that the irregular movements of the planets can be explained if the Earth moves while the Sun stays still,<ref>{{cite book |author=Simplicius |author-link=Simplicius of Cilicia |title=On Aristotle's |year=2003 |url=https://archive.org/details/onaristotlescate00simp |url-access=registration |chapter=Physics 2 |pages=48 |translator-first=Barries |translator-last=Fleet |location=Ithaca |publisher=[[Cornell University Press]]|isbn=9780801441011 }}</ref> but these statements are disputed.<ref>{{cite journal |last=Eastwood |first=Bruce |year=1992 |title=Heraclides and Heliocentrism: Texts, Diagrams, and Interpretations |journal=Journal for the History of Astronomy |volume=23 |issue=4 |pages=253 |doi=10.1177/002182869202300401 |bibcode=1992JHA....23..233E }}</ref>
* {{circa}} '''280 BCE'''&nbsp;– [[Aristarchus of Samos]] offers the [[On the Sizes and Distances (Aristarchus)|first definite discussion]] of the possibility of a [[Heliocentrism|heliocentric cosmos]],<ref>{{cite web |last=Heath |first= Thomas Little |title=Aristarchus of Samos, the ancient Copernicus; a history of Greek astronomy to Aristarchus, together with Aristarchus's Treatise on the sizes and distances of the sun and moon : a new Greek text with translation and notes |url=https://archive.org/details/aristarchusofsam00heatuoft | year=1913 |page=302}}</ref> and uses the size of the Earth's [[shadow]] on the [[Moon]] to estimate the Moon's orbital radius at 60 Earth radii, and its physical radius as one-third that of the Earth. He also makes an inaccurate attempt to measure the distance to the Sun.<ref>{{Cite journal|last=Hirshfeld|first=Alan W.|date=2004|title=The Triangles of Aristarchus |journal=The Mathematics Teacher|volume=97|issue=4|pages=228–231|doi=10.5951/MT.97.4.0228|jstor=20871578 }}</ref>
* {{circa}} '''250 BCE'''&nbsp;– Following the heliocentric ideas of Aristarcus, [[Archimedes]] in his work ''[[The Sand Reckoner]]'' computes the diameter of the universe centered around the Sun to be about 10<sup>14</sup> [[Stadion (unit)|stadia]] (in modern units, about 2 [[light year]]s, {{val|18.93|e=12|ul=km}}, {{val|11.76|e=12|ul=mi}}).<ref name="v">[http://www.lix.polytechnique.fr/Labo/Ilan.Vardi/sand_reckoner.ps Archimedes, The Sand Reckoner 511 R U, by Ilan Vardi], accessed 28-II-2007.</ref>
* {{circa}} '''210 BCE'''&nbsp;– [[Apollonius of Perga]] shows the equivalence of two descriptions of the [[Apparent retrograde motion|apparent retrograde]] planet motions (assuming the geocentric model), one using eccentrics and another [[deferent and epicycle]]s.<ref>Carrol, Bradley and Ostlie, Dale, ''An Introduction to Modern Astrophysics'', 2nd ed., Addison-Wesley, San Francisco, 2007. p. 4 {{ISBN?}}</ref>{{failed verification |date=October 2023}}
* {{circa}} '''200 BCE'''&nbsp;– [[Eratosthenes]] determines that the radius of the Earth is roughly {{convert|6400|km|mi|abbr=on}}.<ref>{{Cite book |last=Russo |first=Lucio |author-link=Lucio Russo|url=https://books.google.com/books?id=MOTpnfz7ZuYC |title=The forgotten revolution : how science was born in 300 BC and why it had to be reborn |date=2004 |publisher=Springer |isbn=3-540-20396-6 |location=Berlin |page=68 |oclc=52945835}}</ref>
* {{circa}} '''150 BCE'''&nbsp;– According to [[Strabo]] (1.1.9), [[Seleucus of Seleucia]] is the first to state that the [[tide]]s are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.<ref>{{cite journal |last=Bartel |first=Leendert van der Waerden |date=1987 |title=The Heliocentric System in Greek, Persian and Hindu Astronomy |journal=Annals of the New York Academy of Sciences |volume=500 |issue=1 |pages=527 |bibcode=1987NYASA.500..525V |doi=10.1111/j.1749-6632.1987.tb37224.x }}</ref>
* {{circa}} '''150 BCE'''&nbsp;– [[Hipparchus]] uses [[parallax]] to determine that the distance to the Moon is roughly {{convert|380000|km|mi|-2|abbr=on}}.<ref>G. J. Toomer, "Hipparchus on the distances of the sun and moon," Archive for History of Exact Sciences '''14''' (1974), 126–142.</ref>
* {{circa}} '''134 BCE'''&nbsp;– Hipparchus discovers the [[precession]] of the [[equinox]]es.<ref>Alexander Jones "Ptolemy in Perspective: Use and Criticism of his Work from Antiquity to the Nineteenth Century, Springer, 2010, p. 36.</ref>
* {{circa}} '''87 BCE'''&nbsp;– The [[Antikythera mechanism]], the earliest known computer, is built. It is an extremely complex astronomical computer designed to predict solar and lunar eclipses accurately and track the movements of the planets and the Sun. It could also calculate the differences in the apsidial and axial precession of heavenly bodies with extreme degree of accuracy.<ref>{{Cite web |last1=Magazine |first1=Smithsonian |last2=Marchant |first2=Jo |title=Decoding the Antikythera Mechanism, the First Computer |url=https://www.smithsonianmag.com/history/decoding-antikythera-mechanism-first-computer-180953979/ |access-date=2022-11-05 |website=Smithsonian Magazine |language=en}}</ref>
* '''28 BCE'''&nbsp;– Chinese history book ''[[Book of Han]]'' makes earliest known dated record of [[sunspot]].<ref>{{
cite journal
 |url         = http://findarticles.com/p/articles/mi_m1310/is_1988_Oct/ai_6955852/
 |year        = 1988
 |title       = The Observation of Sunspots
 |journal     = UNESCO Courier
 |access-date  = 2010-07-14
 |archive-url  = https://archive.today/20120628232645/http://findarticles.com/p/articles/mi_m1310/is_1988_Oct/ai_6955852/
 |archive-date = 2012-06-28
}}</ref>
* {{circa}} '''150 CE'''&nbsp;– [[Claudius Ptolemy]] completes his work ''[[Almagest]]'', that codifies the astronomical knowledge of his time and cements the geocentric model in the West, and it remained the most authoritative text on [[astronomy]] for more than 1,500 years. The ''Almagest'' put forward extremely complex and accurate methods to determine the position and structure of planets, [[star]]s (including some objects as nebulae, [[supernova]]s and galaxies then regarded as stars also) and heavenly bodies. It includes a catalogue of 1,022 stars (largely based on a previous one by Hipparchus of about 850 entries) and a large amount of [[constellation]]s, [[comet]]s and other astronomical phenomena.<ref>{{Cite web |title=Almagest – Ptolemy (Elizabeth) |url=https://projects.iq.harvard.edu/predictionx/almagest-ptolemy-elizabeth |access-date=2022-11-05 |website=projects.iq.harvard.edu |language=en}}</ref> Following a long astrological tradition, he arranged the heavenly spheres ordering them (from Earth outward): Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn and fixed stars.
* {{circa}} '''420'''&nbsp;– [[Martianus Capella]] describes a modified geocentric model, in which the Earth is at rest in the center of the universe and circled by the Moon, the Sun, three planets and the stars, while Mercury and Venus circle the Sun.<ref>Bruce S. Eastwood, ''Ordering the Heavens: Roman Astronomy and Cosmology in the Carolingian Renaissance'' (Leiden: Brill, 2007), pp. 238–39.</ref>

==Middle Ages==
* {{circa}} '''500'''&nbsp;– Indian mathematician-astronomer [[Aryabhata]] accurately computes the solar and lunar eclipses, and the length of Earth's revolution around the Sun.
* {{circa}} '''500'''&nbsp;– Aryabhata discovers the oblique motion of the apsidial precession of the Sun and notes that it is changing with respect to the motion of stars and Earth.
* {{circa}} '''500'''&nbsp;– Aryabhata discovers the rotation of the Earth by conducting [[experiment]]s and giving [[Empirical evidence|empirical]] examples for his theories. He also explains the cause of day and night through the [[Diurnal cycle|diurnal]] rotation of the Earth. He also developed highly accurate models for the orbital motion of the Moon, Mercury and Mars. He also developed a geocentric model of the universe.<ref>{{Cite journal |last=India |first=Digital Branding Learners |date=2019-01-01 |title=Aryabhatta {{as written|the t|he [sic]}} great Indian Mathematicians |url=https://www.academia.edu/38561360 |journal=Learners India}}</ref><ref>{{Cite web |title=Aryabhata – Biography |url=https://mathshistory.st-andrews.ac.uk/Biographies/Aryabhata_I/ |access-date=2022-11-05 |website=Maths History |language=en}}</ref><ref>{{Cite journal |last=Shukla |first=Kripa Shankar |date=1987 |title=Main Characteristics and Achievements of Ancient Indian Astronomy in Historical Perspective |journal=International Astronomical Union Colloquium |language=en |volume=91 |pages=9–22 |doi=10.1017/S0252921100105809 |doi-access=free }}</ref>
* {{circa}} '''620'''&nbsp;– Indian mathematician-astronomer [[Brahmagupta]] describe gravity as a attractive force by the term guruvatkarshan.<ref>{{Cite book |last=Pickover |first=Clifford |url=https://books.google.com/books?id=SQXcpvjcJBUC&pg=PA105 |title=Archimedes to Hawking: Laws of Science and the Great Minds Behind Them |year=2008 |publisher=Oxford University Press |isbn=978-0-19-979268-9 |language=en}}</ref>
* '''628'''&nbsp;– Brahmagupta gives methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and calculations of the [[Solar eclipse|solar]] and [[lunar eclipse]]s.<ref>{{cite magazine |last1=Swain |first1=Mayadhar |title=India's Greatest Mathematician Brahmagupta |magazine=Science Horizon |date=2012 |pages=37–40 |url=https://www.academia.edu/16470812 }}</ref>
* '''820'''&nbsp;– [[Astronomy in medieval Islam|Persian astronomer]], [[Muhammad ibn Musa al-Khwarizmi]], composes his [[Zij]] astronomical tables, utilising [[Arabic numerals]] and the [[Hindu–Arabic numeral system]] in his calculations.<ref name="Thurston1996">{{citation|last=Thurston|first=Hugh|title=Early Astronomy|url=https://books.google.com/books?id=rNpHjqxQQ9oC&pg=PP204|year=1996|publisher=Springer Science & Business Media|isbn=978-0-387-94822-5|pages=204–}}</ref> He also translates Aryabhata's [[Astronomy|astronomical]] and mathematical treatises into Arabic.<ref>{{cite journal|author=Ansari, S.M.R.|date=March 1977|title=Aryabhata I, His Life and His Contributions|journal=Bulletin of the Astronomical Society of India|volume=5|issue=1|pages=10–18|bibcode=1977BASI....5...10A|hdl=2248/502}}</ref>
* '''850'''&nbsp;– [[Al-Farghani]] (Alfraganus) translated and wrote commentary on [[Ptolemy|Ptolemy's]] ''Almagest'' and gave values for the motion of the ecliptic, and the [[axial precession|precessional]] movement of the [[Astronomical object|heavenly bodies]] based on the values given by Ptolemy and Hipparchus.<ref>{{Cite web |last=Saranathan |first=Jayasree |title=No axial precession of the earth proven by Archaeoastronomy of ancient monuments |url=https://www.academia.edu/44178992}}{{self-published inline|date=January 2025}}</ref>
* '''1019'''&nbsp;– [[Al-Biruni]] observes and describes the [[lunar eclipse]] on September 17 in detail and gives the exact latitudes of the stars during it.<ref>{{cite book |doi=10.1017/CBO9780511525186 |title=Historical Eclipses and Earth's Rotation |date=1997 |last1=Stephenson |first1=F. Richard |isbn=978-0-521-46194-8 |chapter=Observations of eclipses by medieval Arab astronomers |pages=456–500 }}</ref>[[File:Lunar phases al-Biruni.jpg|thumb|right|An annotated diagram explaining the [[phases of the moon]] from one of al-Biruni's astronomical works. Sun (far right) – Earth (far left) and Lunar phases]]
* {{circa}} '''1030'''&nbsp;– In his major astronomical work, the ''Mas'ud Canon'', Al-Biruni observed that, contrary to Ptolemy, the Sun's [[apogee]] (highest point in the heavens) was mobile, not fixed.<ref>{{cite web |author=Covington, Richard|title=Rediscovering Arabic Science|website=Aramco World|access-date=5 October 2018|url=http://archive.aramcoworld.com/issue/200703/rediscovering.arabic.science.htm}}</ref>
* {{circa}} '''1060'''&nbsp;– [[Al-Andalus|Andalusi]] astronomer [[Al-Zarqali]] corrects geographical data from [[Ptolemy]] and [[Al-Khwarizmi]], specifically by correcting Ptolemy's estimate of the longitude of the [[Mediterranean Sea]] from 62 degrees to the correct value of 42 degrees.<ref name="isesco.org.ma">{{cite web|url=http://www.isesco.org.ma/english/publications/Architects/P24.php |title=Islamic Educational, Scientific and Cultural Organization – ISESCO |access-date=2011-10-08 |url-status=dead |archive-url=https://web.archive.org/web/20120331211945/http://www.isesco.org.ma/english/publications/Architects/P24.php |archive-date=2012-03-31 }}</ref> He was the first to demonstrate the motion of the [[apsis|solar apogee]] relative to the fixed background of the stars, measuring its rate of motion as 12.9 seconds per year, which is remarkably close to the modern calculation of 11.77 seconds.<ref>{{Citation | last = Toomer | first = G. J. | author-link =G. J. Toomer | title = The Solar Theory of az-Zarqāl: A History of Errors  | journal = Centaurus | volume = 14 | issue = 1 | pages = 306–36 | date = 1969 | doi = 10.1111/j.1600-0498.1969.tb00146.x |bibcode = 1969Cent...14..306T }}, at pp. 314–17.</ref> Al-Zarqālī also contributed to the famous ''[[Tables of Toledo]]''.
* {{circa}} '''1175'''&nbsp;– [[Gerard of Cremona]] translates Ptolemy's ''[[Almagest]]'' from [[Arabic]] into [[Latin]].<ref>{{cite journal |last1=Kunitzsch |first1=Paul |title=The Star Catalogue Commonly Appended to the Alfonsine Tables |journal=Journal for the History of Astronomy |date=May 1986 |volume=17 |issue=2 |pages=89–98 |doi=10.1177/002182868601700202 |bibcode=1986JHA....17...89K |bibcode-access=free }}</ref>
* {{circa}} '''1200'''&nbsp;– [[Fakhr al-Din al-Razi]], in dealing with his conception of physics and [[Islamic cosmology|the physical world]], rejected the [[Aristotelianism|Aristotelian]] and [[Avicennism|Avicennian]] view of a single world, but instead proposed that there are "a thousand thousand worlds (''alfa alfi 'awalim'') beyond this world such that each one of those worlds be bigger and more massive than this world as well as having the like of what this world has."<ref name="Setia">{{citation|title=Fakhr Al-Din Al-Razi on Physics and the Nature of the Physical World: A Preliminary Survey |first=Adi |last=Setia |journal=Islam & Science |volume=2 |date=2004 |url=http://findarticles.com/p/articles/mi_m0QYQ/is_2_2/ai_n9532826/ |archive-url=https://archive.today/20120710164222/http://findarticles.com/p/articles/mi_m0QYQ/is_2_2/ai_n9532826/ |url-status=dead |archive-date=2012-07-10 |access-date=2010-03-02 }}</ref>
[[Image:Tablas alfonsies.jpg|thumb|300px|Alfonsine Tables]]
* '''1252'''&nbsp;– [[Alfonso X of Castile]] sponsored the creation and compilation of the ''[[Alfonsine Tables]]'' by scholars he assemble in the [[Toledo School of Translators]] in [[Toledo, Spain]].<ref>{{cite journal|title=Alfonsine tables|journal=Enciclopedia Columbia|date=2018|publisher=Columbia University Press|quote=a revision and improvement of the Ptolemaic tables and were compiled at Toledo, Spain, by about 50 astronomers assembled for the purpose by Alfonso X of Castile}}</ref> These astronomical tables were used and updated during the following three centuries, as the main source of astronomical data, mainly to calculate [[ephemerides]] (which were in turn used by [[astrology|astrologers]] to cast [[horoscopes]]).<ref>Owen Gingerich, ''Gutenberg's Gift'' pp. 319–28 in ''Library and information services in astronomy V'' (Astron. Soc. Pacific Conference Series vol. 377, 2007).</ref>
* {{circa}} '''1300'''&nbsp;– [[Jews|Jewish]] astronomer [[Gersonides|Levi ben Gershon]] (Gersonides) recognized that the stars are much larger than the planets. Gersonides appears to be among the few astronomers before modern times, along Aristarcus, to have surmised that the fixed stars are much further away than the planets. While all other astronomers put the fixed stars on a rotating sphere just beyond the outer planets, Gersonides estimated the distance to the fixed stars to be no less than 159,651,513,380,944 Earth radii, or about 100,000 light-years in modern units.<ref>{{Cite journal |last=Kennedy |first=E. S. |date=1986-06-01 |title=The Astronomy of Levi ben Gerson (1288–1344): A Critical Edition of Chapters 1–20 with Translation and Commentary. Levi ben Gerson, Bernard R. Goldstein |journal=Isis |volume=77 |issue=2 |pages=371–372 |doi=10.1086/354184 }}</ref><ref>{{Cite journal |last=Goldstein |first=Bernard R. |date=November 1996 |title=Levi Ben Gerson and the Brightness of Mars |journal=Journal for the History of Astronomy |volume=27 |issue=4 |pages=297–300 |doi=10.1177/002182869602700402 |bibcode=1996JHA....27..297G }}</ref>
* {{circa}} '''1350'''&nbsp;– [[Ibn al-Shatir]] anticipates Copernicus by abandoning the [[equant]] of [[Claudius Ptolemy|Ptolemy]] in his calculations of planetary motion,<ref>{{Cite journal | volume = 117| issue = 6| page = 424| last = Swerdlow| first = Noel M.| title = The Derivation and First Draft of Copernicus's Planetary Theory: A Translation of the Commentariolus with Commentary| journal = Proceedings of the American Philosophical Society| date = 1973-12-31| jstor = 986461| bibcode = 1973PAPhS.117..423S}}</ref> and he provides a proto [[empirical]] model of [[Moon|lunar]] motion which accurately matches [[observation]]s.<ref>{{Cite journal|last=Abbud|first=Fuad|date=1962|title=The Planetary Theory of Ibn al-Shatir: Reduction of the Geometric Models to Numerical Tables|journal=The University of Chicago Press|volume=53|pages=492–499|jstor=}}</ref>
* {{circa}} '''1350'''&nbsp;– [[Nicole Oresme]] put forward several revolutionary theories like [[mean speed theorem]], which he used in calculating the position and shape of the planetary orbits, measuring the apsidial and [[axial precession]] of the [[Lunar distance (astronomy)|lunar]] and solar [[orbit]]s, measuring the angles and distance between ecliptics and calculating stellar and [[Planetary science|planetary]] distances. In his ''Livre du Ciel et du Monde'', Oresme discussed a range of evidence for the daily rotation of the [[Earth]] on its [[Axial tilt|axis]].<ref>{{Citation |last=Kirschner |first=Stefan |title=Nicole Oresme |date=2021 |url=https://plato.stanford.edu/archives/fall2021/entries/nicole-oresme/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |edition=Fall 2021 |publisher=Metaphysics Research Lab, Stanford University |access-date=2022-11-05}}</ref><ref>{{Cite book |last=Wallace |first=William A. |url=https://books.google.com/books?id=2Ix6kR6iN-UC&pg=PA42 |title=Prelude to Galileo: Essays on Medieval and Sixteenth-Century Sources of Galileo's Thought |year= 1981 |publisher=Springer Netherlands |isbn=978-90-277-1216-5 |pages= |language=en}}</ref>
* '''1440'''&nbsp;– [[Nicholas of Cusa]] proposes that the Earth rotates on its axis in his book, ''On Learned Ignorance''.<ref name=cathen>{{cite encyclopedia |author=Hagen, J.|title=Nicholas of Cusa |encyclopedia=The Catholic Encyclopedia |volume=11 |publisher=Robert Appleton Company |year=1911 |url =http://www.newadvent.org/cathen/11060b.htm |access-date =2008-10-13}}</ref> Like Oresme, he also wrote about the possibility of the plurality of worlds.<ref>Dick, Steven J. Plurality of Worlds: The Extraterrestrial Life Debate from Democritus to Kant. Cambridge University Press (June 29, 1984). pp. 35–42.</ref>

== 16th century ==
{{See also|Scientific Revolution|Age of Discovery}}
* '''1501'''&nbsp;– Indian astronomer [[Nilakantha Somayaji]] proposes a universe in which the planets orbit the Sun, but the Sun orbits the Earth.<ref name=Joseph>George G. Joseph (2000). ''The Crest of the Peacock: Non-European Roots of Mathematics'', p. 421. [[Princeton University Press]]. {{ISBN?}}</ref>
* {{circa}} '''1514'''&nbsp;– [[Nicolaus Copernicus]] states his [[Heliocentrism|heliocentric]] theory in ''[[Commentariolus]]''.<ref>{{cite book |title=The Astronomical Revolution: Copernicus – Kepler – Borelli |last=Koyré |first=Alexandre |author-link=Alexandre Koyré |publisher=Cornell University Press |date=1973 |isbn=978-0-8014-0504-4 |location=Ithaca, New York |pages= 18–28}}; {{harvtxt|Swerdlow|1973|pp=423–24}}</ref><ref>{{cite book |title=The manuscripts of Nicholas Copernicus' minor works; facsimiles |first=Nicolaus |last=Copernicus |author-link= Nicolaus Copernicus |editor-first=Pawel |editor-last=Czartoryski |publisher=Polish Academy of Sciences |location=Krakow |url=http://www.kpbc.ukw.edu.pl/dlibra/plain-content?id=48794 |date=1992 |isbn=83-01-10562-3 |pages=20, 208–52}}</ref><ref>{{cite book | title = Three Copernican Treatises:The Commentariolus of Copernicus; The Letter against Werner; The Narratio Prima of Rheticus | translator-last=Rosen |translator-first=Edward | publisher=Dover Publications | edition = Second Edition, revised | year = 2004 | orig-year = 1939 | isbn = 978-0-486-43605-0 | location = New York |pages=6–7 & 57–90 |url=https://books.google.com/books?id=ceSnipu4MykC}}.</ref>
* '''1522'''&nbsp;– First [[Magellan's circumnavigation|circumnavigation of the world]] by [[Ferdinand Magellan|Magellan]]-[[Juan Sebastián Elcano|Elcano]] expedition shows that the Earth is, in effect, a [[Figure of the Earth|sphere]].<ref>{{Cite book|author=Nancy Smiler Levinson|title=Magellan and the First Voyage Around the World|url=https://books.google.com/books?id=1PbBzjBuW8IC&pg=PA39|access-date=31 July 2010|year=2001|publisher=Houghton Mifflin Harcourt|isbn=978-0-395-98773-5}}</ref>
* '''1543'''&nbsp;– Copernicus publishes his heliocentric theory in ''[[De revolutionibus orbium coelestium]]''.<ref>{{cite book|title=History of the planetary systems from Thales to Kepler|year=1906|first=John L E|last=Dreyer|page=[https://archive.org/details/historyofplaneta00dreyuoft/page/342 342]|publisher=Cambridge University Press|url=https://archive.org/details/historyofplaneta00dreyuoft}}</ref>
* '''1576'''&nbsp;– [[Tycho Brahe]] founds the first modern astronomical observatory in modern [[Europe]], [[Uraniborg]].<ref name="Westman2011">{{cite book|last=Westman|first=Robert S.|title=The Copernican Question: Prognostication, Skepticism, and Celestial Order|url=https://books.google.com/books?id=iEueQqLQyiIC&pg=PA236|access-date=August 7, 2013|year=2011|publisher=[[University of California Press]]|isbn=9780520948167|page=236}}</ref>[[File:Tycho-Brahe-Mural-Quadrant.jpg|thumb|right|Engraving of the mural quadrant from Brahe's book ''Astronomiae instauratae mechanica'' (1598)]]
* '''1577'''&nbsp;– Tycho Brahe records the position of the [[Great Comet of 1577|Great Comet of that year]] as viewed from Uraniborg (in the island [[Hven]], near [[Copenhagen]]) and compares it with that observed by [[Tadeáš Hájek|Thadaeus Hagecius]] from [[Prague]] at the same time, giving deliberate consideration to the movement of the Moon. It was discovered that, while the comet was in approximately the same place for both of them, the Moon was not, and this meant that the comet was much further out, contrary to what was previously conceived as an atmospheric phenomenon.<ref>{{cite book |author1=R. Lang, Kenneth|author2=Charles Allen Whitney|date=1991|title=Wanderers in Space|publisher=CUP Archive|pages=240|isbn=978-0-521-42252-9}}</ref>
* '''1582'''&nbsp;– Pope [[Pope Gregory XIII|Gregory XIII]] introduces the [[Gregorian calendar]], an enhanced solar calendar more accurate than the previous Roman [[Julian calendar]].<ref>{{ Cite book |author1=Dershowitz, D.|author2=Reingold, E. M|date=2008|title=[[Calendrical Calculations]] |edition=3rd |publisher=Cambridge University Press|page=45|quote=The calendar in use today in most of the world is the Gregorian or new-style calendar designed by a commission assembled by Pope Gregory XIII in the sixteenth century}}</ref> The principal change was to space [[leap year]]s differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day [[Tropical year|'tropical' or 'solar']] year that is determined by the Earth's revolution around the Sun. The reform advanced the date by 10 days: Thursday 4 October 1582 was followed by Friday 15 October 1582. The Gregorian calendar is still in use today.
* '''1584'''&nbsp;– [[Giordano Bruno]] published two important philosophical dialogues (''La Cena de le Ceneri'' and ''De l'infinito universo et mondi'') in which he argued against the planetary spheres and affirmed the Copernican principle. Bruno's infinite universe was filled with a substance{{snd}}a "pure air", [[Aether (classical element)|aether]], or ''spiritus''{{snd}}that offered no resistance to the heavenly bodies which, in Bruno's view, rather than being fixed, moved under their own [[Impetus (mechanics)|impetus]] (momentum). Most dramatically, he completely abandoned the idea of a hierarchical universe. Bruno's cosmology distinguishes between "suns" which produce their own light and heat, and have other bodies moving around them; and "earths" which move around suns and receive light and heat from them. Bruno suggested that some, if not all, of the objects classically known as [[fixed stars]] are in fact suns,<ref name="thirddialogue">{{cite book |last=Bruno |first=Giordano |title=On the infinite universe and worlds |chapter=Third Dialogue |chapter-url=http://www.positiveatheism.org/hist/brunoiuw3.htm |url-status=dead |archive-url=https://web.archive.org/web/20120427091405/http://www.positiveatheism.org/hist/brunoiuw3.htm |archive-date=27 April 2012}}</ref> so he was arguably the first person to grasp that "stars are other suns with their own planets." Bruno wrote that other worlds "have no less virtue nor a nature different from that of our Earth" and, like Earth, "contain animals and inhabitants".<ref>{{cite web |url=http://www.positiveatheism.org/hist/brunoiuw0.htm#IUW0III |title=Giordano Bruno: On the Infinite Universe and Worlds (De l'Infinito Universo et Mondi) Introductory Epistle: Argument of the Third Dialogue |access-date=4 October 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141013120648/http://www.positiveatheism.org/hist/brunoiuw0.htm#IUW0III |archive-date=13 October 2014  }}</ref>
* '''1588'''&nbsp;– Tycho Brahe publishes his own [[Tychonic system]], a blend between Ptolemy's classical geocentric model and Copernicus' heliocentric model, in which the Sun and the Moon revolve around the Earth, in the center of universe, and all other planets revolve around the Sun.<ref>{{cite web|last1=Hatch|first1=Robert|title=Early Geo-Heliocentric models|url=http://users.clas.ufl.edu/ufhatch/pages/03-Sci-Rev/SCI-REV-Home/resource-ref-read/chief-systems/08-0TYCHO5-WSYS.html|website=The Scientific Revolution|publisher=Dr. Robert A. Hatch|access-date=11 April 2018}}</ref>

== 17th century ==
* '''1600'''&nbsp;– [[William Gilbert (physician)|William Gilbert]] with his model called the [[terrella]], shows the Earth behaves like a huge but low intensity [[magnet]] with its own [[Earth's magnetic field|magnetic field]], which explains the behaviour of the [[compass]] pointing to the [[Poles of astronomical bodies#Magnetic poles|magnetic poles]].<ref>{{cite journal |last1=Malin |first1=Stuart |last2=Barraclough |first2=David |title=Gilbert's De Magnete: An early study of magnetism and electricity |journal=Eos, Transactions American Geophysical Union |date=2000 |volume=81 |issue=21 |pages=233 |doi=10.1029/00EO00163 |bibcode=2000EOSTr..81..233M |url=http://www.phy6.org/earthmag/demagrev.htm |access-date=6 November 2018|doi-access= |url-access=subscription }}</ref>
* '''1604'''&nbsp;– [[Galileo Galilei]] correctly hypothesized that the distance of a falling object is proportional to the [[Square (algebra)|square]]  of the time elapsed.<ref>{{cite book|last=Gillispie|first=Charles Coulston|url=https://archive.org/details/edgeofobjectivit00char/page/n13/mode/2up|title=The Edge of Objectivity: An Essay in the History of Scientific Ideas|publisher=Princeton University Press|year=1960|isbn=0-691-02350-6|pages=3–6|author-link=Charles Coulston Gillispie}}</ref>
* '''1609'''&nbsp;– [[Johannes Kepler]] states his first two empirical [[Kepler's laws of planetary motion|laws of planetary motion]], stating that the orbits of the planets around the Sun are elliptical rather than circular, and thus resolving many ancient problems with planetary models, without the need of any epicycle.<ref>Astronomia nova Aitiologitis, seu Physica Coelestis tradita Commentariis de Motibus stellae Martis ex observationibus G.V. Tychnonis. Prague 1609; Engl. tr. W.H. Donahue, Cambridge 1992.</ref>
* '''1609'''&nbsp;– Galileo Galilei starts to make [[telescope]]s with about 3x up to 30x magnification, based only on descriptions of the first practical telescope which [[Hans Lippershey]] tried to patent in the [[Netherlands]] in 1608.<ref>{{cite book |author=King, C. C.|date=2003|title=The History of the Telescope|publisher=Dover Publications|pages=30–32|isbn=978-0-486-43265-6}}</ref> With a [[Refracting telescope#Galilean telescope|Galilean telescope]], the observer could see magnified, upright images on the Earth{{snd}}what is commonly known as a ''spyglass''{{snd}}but also it can be used to observe the sky, a key tool for further astronomical discoveries.[[File:Bertini_fresco_of_Galileo_Galilei_and_Doge_of_Venice.jpg|thumb|right|Galileo showing the [[Doge of Venice]] how to use the telescope (fresco by [[Giuseppe Bertini]])]][[File:Ole Rømer at work.jpg|thumb|right|Ole Rømer at work]]
* '''1609'''&nbsp;– Galileo Galilei aimed his telescope at the [[Moon]]. While not being the first person to observe the Moon through a telescope (English mathematician [[Thomas Harriot]] had done it four months before but only saw a "strange spottednesse"),<ref>{{cite book |author1=Edgerton, Samuel Y.|date=2009|title=The Mirror, the Window, and the Telescope: How Renaissance Linear Perspective Changed Our Vision of the Universe|publisher=Cornell University Press|pages=155–159|isbn=978-0-8014-7480-4}}</ref> Galileo was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and [[Impact crater|crater]]s. He also estimated the heights of that mountains. The Moon was not what was long thought to have been a translucent and perfect sphere, as [[Aristotle]] claimed, and hardly the first "planet".
* '''1610'''&nbsp;– Galileo Galilei observes the [[Galilean moons|four main]] [[moons of Jupiter]]: [[Callisto (moon)|Callisto]], [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], and [[Io (moon)|Io]];<ref>{{cite book |author=Drake, S.|date=1978|title=Galileo at Work|publisher=University of Chicago Press|pages=152|isbn=978-0-226-16226-3}}</ref> sees [[Saturn]]'s [[planetary ring]]s (but does not recognize that they are rings),<ref>{{cite web |author=Cain, Fraser|date=3 July 2008|title=History of Saturn|website=Universe Today|url=http://www.universetoday.com/15390/history-of-saturn|access-date=5 October 2020}}</ref> and observes the [[phases of Venus]],<ref>[http://www.astro.umd.edu/~miller/ASTR100/class6.pdf Galileo's observations of the phases of Venus (slide 4)]</ref> disproving the [[Ptolemaic system]] though not the [[geocentric model]].
* '''1619'''&nbsp;– Johannes Kepler states his [[Kepler's laws of planetary motion#Third law|third]] empirical law of planetary motion, which relates the distance and period of the planetary orbits.<ref>{{cite book|title=Physics, the Human Adventure: From Copernicus to Einstein and Beyond |author=Holton, Gerald James |author2=Brush, Stephen G.  |pages=40–41|url=https://books.google.com/books?id=czaGZzR0XOUC&pg=PA40 |edition=3rd paperback |isbn=978-0-8135-2908-0 |publisher=Rutgers University Press|location=Piscataway, NJ |access-date=December 27, 2009 |date=2001}}</ref>
* '''1631'''&nbsp;– [[Pierre Gassendi]] is the first to observe the [[transit of Mercury]]. He was surprised by the small size of the planet compared to the Sun.<ref>{{cite journal |title=The Importance of the Transit of Mercury of 1631 |last=van Helden |first=Albert |journal=Journal for the History of Astronomy |volume=7 |page=1 |date=1976 |doi=10.1177/002182867600700101 |bibcode=1976JHA.....7....1V }}</ref>
* '''1632'''&nbsp;– Galileo Galilei is sometimes credited with the discovery of the [[Libration#Lunar libration|lunar libration in latitude]],<ref name="OnMoonLibration">{{cite book |editor=Bergeron, Jacqueline |date=2013|title=Highlights of Astronomy: As Presented at the XXIst General Assembly of the IAU, 1991|publisher=Springer Science & Business Media|pages=521|isbn=978-94-011-2828-5}}</ref>  although Thomas Harriot or [[William Gilbert (physician)|William Gilbert]] might have done so before.<ref>{{cite journal |author=Stephen Pumfrey |date=15 April 2009|title=Harriot's maps of the Moon: new interpretations |journal=Notes and Records of the Royal Society |volume=63|issue=2|pages=163–168|doi=10.1098/rsnr.2008.0062 }}</ref>
* '''1639'''&nbsp;– [[Jeremiah Horrocks]] and his friend and correspondent [[William Crabtree]] are the first astronomers known to [[1639 transit of Venus|observe and record]] a [[transit of Venus]].<ref>{{cite web |url=http://www.dioi.org/kn/birth.htm |title=Horrocks and the Dawn of British Astronomy |last=Kollerstrom |first=Nicholas |date=1998 |publisher=University College London |access-date=11 May 2012 }}</ref>
* '''1643'''&nbsp;– [[Evangelista Torricelli]], disciple of Galileo, builds an elementary [[barometer]], which shows that the [[Atmospheric pressure|air weighs]], and incidentally creating the first artificial [[vacuum]] in a laboratory.<ref>{{cite book |last=Gillispie |first=Charles Coulston |author-link=Charles Coulston Gillispie |title=The Edge of Objectivity: An Essay in the History of Scientific Ideas |url=https://archive.org/details/edgeofobjectivit0000gill |url-access=registration |year=1960 |publisher=Princeton University Press |isbn=0-691-02350-6 |page=[https://archive.org/details/edgeofobjectivit0000gill/page/100 100]}}</ref>
* '''1648'''&nbsp;– [[Johannes Hevelius]] discovers the [[Libration#Lunar libration|lunar libration in longitude]].<ref name="OnMoonLibration" /> It can reach 7°54′ in [[amplitude]].<ref name="Ratkowski">{{cite web |first1=Rob |last1=Ratkowski |first2=Jim |last2=Foster |url=https://epod.usra.edu/blog/2014/05/libration-of-the-moon.html |work=Earth Science Picture of the Day |date=May 31, 2014 |title=Libration of the Moon}}</ref>
* '''1648'''&nbsp;– [[Blaise Pascal]], aided by his brother-in-law Florin Périer at mount [[Puy de Dôme]], shows that air pressure on a high mountain is less than at a lower altitude, proving his idea that, as air has a finite weight, Earth's atmosphere must have a maximum height.<ref>{{cite journal |author=Ley, Willy|date=June 1966|title=For Your Information|journal=Galaxy Science Fiction|pages=94–106}}</ref>
* '''1655'''&nbsp;– [[Giovanni Domenico Cassini]] and [[Robert Hooke]] separately discover Jupiter's [[Great Red Spot]].<ref>{{cite book |author=Rogers, John H.|date=1995|title=The Giant Planet Jupiter|publisher=Cambridge University Press|pages=6|isbn=978-0521410083}}</ref>
* '''1656'''&nbsp;– [[Christiaan Huygens]] identifies [[Rings of Saturn|Saturn's rings]] as rings and discovers its moon [[Titan (moon)|Titan]].<ref>{{cite web|url=https://assets.cambridge.org/052179/3483/sample/0521793483ws.pdf |title=Lifting Titan's Veil |publisher=Cambridge |archive-url=https://web.archive.org/web/20050222073209/https://assets.cambridge.org/052179/3483/sample/0521793483ws.pdf |archive-date=February 22, 2005|page=4}}</ref>
* '''1659'''&nbsp;– Huygens estimated a value of about 24,000 Earth radii for the [[Astronomical unit|distance Earth-Sun]], remarkably close to modern values but he was based on many unproven (and incorrect) assumptions; the accuracy of his value seems to be based more on luck than good measurement, with his various errors cancelling each other out.<ref>{{cite journal |bibcode=1985Obs...105...32G|title=Christiaan Huygens' measurement of the distance to the Sun|journal=The Observatory|volume=105|pages=32|last1=Goldstein|first1=S. J.|year=1985}}</ref>
* '''1665'''&nbsp;– Cassini determines the rotational speeds of Jupiter, Mars, and Venus.<ref name="CassiniOnSaturn">{{cite journal|last=Van Helden|first=Albert|title=The beginnings, from Lipperhey to Huygens and Cassini|journal=Experimental Astronomy|volume=25|issue=1–3|doi=10.1007/s10686-009-9160-y|year=2009|page=3|bibcode=2009ExA....25....3V|doi-access=free}}</ref>
* '''1668'''&nbsp;– [[Isaac Newton]] builds [[Newton's reflector|his own]] [[reflecting telescope]], the first fully functional of this kind, and a landmark for future developings as it reduces [[spherical aberration]] with no [[chromatic aberration]].<ref name="books.google.com">{{cite book|author=A. Rupert Hall|title=Isaac Newton: Adventurer in Thought|url=https://archive.org/details/isaacnewtonadven0000hall|url-access=registration|year=1996|publisher=Cambridge University Press|isbn=978-0-521-56669-8|page=[https://archive.org/details/isaacnewtonadven0000hall/page/67 67]}}</ref>
* '''1672'''&nbsp;– Cassini discovers Saturn's moons [[Iapetus (moon)|Iapetus]] and [[Rhea (moon)|Rhea]].<ref name="CassiniOnSaturn" />
* '''1672'''&nbsp;– [[Jean Richer]] and Cassini measure the Earth-Sun distance, the [[astronomical unit]], to be about 138,370,000&nbsp;km.<ref>{{cite web|url=http://www.scientificamerican.com/article.cfm?id=astronomical-unit-or-earth-sun-distance-gets-an-overhaul|title='Astronomical Unit', or Earth-Sun Distance, Gets an Overhaul|website=[[Scientific American]] }}</ref>
* '''1675'''&nbsp;– [[Ole Rømer]] uses the orbital mechanics of Jupiter's [[natural satellite|moons]] to estimate that the [[speed of light]] is about 227,000&nbsp;km/s.<ref>{{cite journal |last1=Bobis |first1=Laurence |last2=Lequeux |first2=James |title=Cassini, Rømer and the velocity of light |journal=Journal of Astronomical History and Heritage |date=July 2008 |volume=11 |issue=2 |pages=97–105 |doi=10.3724/SP.J.1440-2807.2008.02.02 |bibcode=2008JAHH...11...97B |bibcode-access=free }}</ref>
* '''1675'''&nbsp;– Cassini discovers the main division in the rings of Saturn, named after him, the [[Cassini Division]].<ref>{{cite book|last=Cassini, Gian Domenico (Jean-Dominique) (Cassini I) |title=Complete Dictionary of Scientific Biography|date=2008|publisher=Detroit: Charles Scribner's Sons|pages=100–104}}</ref>
* '''1686'''&nbsp;– Cassini discovers Saturn's moons [[Tethys (moon)|Tethys]] and [[Dione (moon)|Dione]].<ref name="CassiniOnSaturn" />
* '''1687'''&nbsp;– Isaac Newton publishes his [[Newton's law of universal gravitation|law of universal gravitation]] in his work ''[[Philosophiæ Naturalis Principia Mathematica]]''.<ref>{{cite book|page=[https://archive.org/details/bub_gb_6EqxPav3vIsC/page/n244 220]|url=https://archive.org/details/bub_gb_6EqxPav3vIsC|title=The Mathematical Principles of Natural Philosophy, Volume II|publisher=Benjamin Motte|last1=Newton|first1=Sir Isaac|date=1729}}</ref>
* '''1690'''&nbsp;– Cassini observes [[differential rotation]] within Jupiter's atmosphere.<ref name="CassiniOnSaturn" />

==18th century==
[[File:Solar eclipse 1715May03 Halley map.png|thumb|upright|Halley's map of the path of the [[Solar eclipse of 3 May 1715]] across England]]
* '''1704'''&nbsp;– [[John Locke]] enters the term "[[Solar System]]" in the English language, when he used it to refer to the Sun, planets, and comets as a whole.<ref>{{cite web | title=solar (adj.) | website=Online Etymology Dictionary | url=https://www.etymonline.com/word/solar | access-date=2 May 2022 | archive-date=18 March 2022 | archive-url=https://web.archive.org/web/20220318002833/https://www.etymonline.com/word/solar | url-status=live }}</ref>
* '''1705'''&nbsp;– [[Edmond Halley]] publicly predicts the periodicity of the [[Halley's Comet|comet of 1682]] and computes its expected path of return in 1757.<ref>{{Cite book |last=Lancaster-Brown |first=Peter |title=Halley & His Comet |publisher=Blandford Press |date=1985|pages=78 |isbn=0-7137-1447-6 |url=https://archive.org/details/halleyhiscomet00pete }}</ref>
* '''1715'''&nbsp;– Edmond Halley calculates the shadow path of a solar eclipse.<ref name="WestfallSheehan2014">{{cite book|last1=Westfall|first1=John|last2=Sheehan|first2=William|title=Celestial Shadows: Eclipses, Transits, and Occultations|url=https://books.google.com/books?id=W9mLBQAAQBAJ&pg=PA115|year=2014|publisher=Springer|isbn=978-1-4939-1535-4|page=115}}</ref>
* '''1716'''&nbsp;– Edmond Halley suggests a high-precision measurement of the Sun-Earth distance by timing the [[transit of Venus]].<ref>{{cite journal|title=Jeremiah Horrocks, William Crabtree, and the Lancashire observations of the transit of Venus of 1639|author=Allan Chapman|journal=Proceedings of the International Astronomical Union |date=2004|volume=2004 |pages=3–26 |publisher=Cambridge University Press|doi=10.1017/S1743921305001225 |doi-access=free}}</ref>
* '''1718'''&nbsp;– Edmond Halley discovers [[proper motion]] of stars, dispelling the concept of the "[[fixed stars]]".<ref>{{cite book |title=A History of Ancient Mathematical Astronomy |author=Otto Neugebauer |url=https://books.google.com/books?id=vO5FCVIxz2YC&q=proper+motion+angle&pg=PA1085 |page= 1084 |isbn=978-3-540-06995-9 |publisher=Birkhäuser |date=1975}}</ref>
* '''1729'''&nbsp;– [[James Bradley]] determines the cause of the [[aberration of starlight]], providing the first direct evidence of the Earth's motion, and a more accurate method to compute the speed of light.<ref>{{cite journal |last=Bradley |first=James |title=A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and F.R.S. to Dr. Edmond Halley Astronom. Reg. &c. Giving an Account of a New Discovered Motion of the Fix'd Stars. |date=1727–1728 |doi = 10.1098/rstl.1727.0064 |journal=Phil. Trans. R. Soc. |volume=35 |issue=406 |pages=637–661|bibcode=1727RSPT...35..637B|doi-access=free}}</ref>
* '''1735–1739'''&nbsp;– The [[French Academy of Sciences]] sends two expeditions to measure the oblateness of the Earth by measuring the length of a degree of latitude at two locations: one to [[Lapland (Finland)|Lapland]], close to the [[Arctic Circle]] and other to the [[Equator]], the [[French Geodesic Mission]]. Their measurements show that the Earth is an [[Spheroid|oblate spheroid]] flattened at the [[Geographical pole|pole]]s.<ref>{{Cite web|url=https://gallica.bnf.fr/ark:/12148/bpt6k5470853s|title=La Vie des sciences|last=Levallois|first=Jean-Jacques|date=1986|website=Gallica|pages=277–284, 288|access-date=2019-05-22}}</ref>
* '''1749'''&nbsp;– [[Pierre Bouguer]], part of French Geodesic Mission, publish that he and [[Charles Marie de La Condamine]] had been able to detect a deflection of a [[pendulum]]'s [[plumb-bob]] of 8&nbsp;[[second of arc|seconds of arc]] in the proximity of the volcano [[Chimborazo (volcano)|Chimborazo]].<ref>{{Cite book|last=Poynting|first=J. H.|title=The mean density of the earth|date=1894|pages=12–22|url=https://archive.org/download/meandensityofear00poynuoft/meandensityofear00poynuoft.pdf}}</ref> Although not enough to measure the value of the [[gravitational constant]] accurately, the experiment had at least proved that the Earth could not be a [[Hollow Earth|hollow shell]], as some thinkers of the day had suggested.<ref>{{cite book|last=Poynting|first=J.H.|title=The Earth: its shape, size, weight and spin|publisher=Cambridge|date=1913 |pages=50–56 |url=https://books.google.com/books?id=whA9AAAAIAAJ&pg=PA50}}</ref>
* {{circa}} '''1750'''&nbsp;– The three collinear [[Lagrange point]]s (L1, L2, L3) were discovered by [[Leonhard Euler]], a decade before [[Joseph-Louis Lagrange]] discovered the remaining two.<ref>{{Cite book |title=Dynamical Systems, the Three-Body Problem, and Space Mission Design |last1=Koon |first1=W. S. |first2=M. W. |last2=Lo |first3=J. E. |last3=Marsden |first4=S. D. |last4=Ross |url=http://www.cds.caltech.edu/~marsden/books/Mission_Design.html |date=2006 |page=9 |access-date=2008-06-09 |archive-url=https://web.archive.org/web/20080527145955/http://www.cds.caltech.edu/~marsden/books/Mission_Design.html |archive-date=2008-05-27 |url-status=dead }} (16MB)</ref><ref name="E327">{{cite book|author-link=Leonhard Euler|first=Leonhard|last=Euler |url=http://www.math.dartmouth.edu/~euler/docs/originals/E327.pdf |title=De motu rectilineo trium corporum se mutuo attrahentium |date=1765}}</ref>
* '''1752'''&nbsp;– [[Benjamin Franklin]] conducts his [[Benjamin Franklin#Kite experiment and lightning rod|kite experiment]], successfully extracting sparks from a cloud, showing that [[lightning]] bolts are huge natural [[Electricity|electrical]] discharges.<ref>{{cite book |author=Wolf, Abraham |date=1939 |title=History of Science, Technology, and Philosophy in the Eighteenth Century|publisher=New York: Macmillan|pages=232}}</ref>
* '''1755'''&nbsp;– [[Immanuel Kant]] first formulates the [[nebular hypothesis]] of Solar System formation.<ref>{{cite journal|last= Woolfson|first= M.M.|title= Solar System&nbsp;– its origin and evolution|journal= Q. J. R. Astron. Soc.|volume= 34| pages= 1–20|date= 1993|bibcode= 1993QJRAS..34....1W}} For details of Kant's position, see Stephen Palmquist, "Kant's Cosmogony Re-Evaluated", ''Studies in History and Philosophy of Science'' 18:3 (September 1987), pp. 255–269.</ref>
* '''1758'''&nbsp;– [[Johann Palitzsch]] observes the return of the comet that Edmond Halley had anticipated in 1705.<ref>Hoffmann, Christian Gotthold (1759 January 20) "Nachricht von dem Kometen, welcher seit dem 25. December gesehen wird" (News of the comet, which has been seen since the 25th of December), ''Dreßdnischen Gelehrten Anzeigen'', 2nd issue.</ref> The gravitational attraction of Jupiter had slowed the return by 618 days. Parisian astronomer [[La Caille]] suggests it should be named "Halley's Comet".<ref>{{cite journal |title=The history of Halley's Comet |journal=Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences |date=30 September 1987 |volume=323 |issue=1572 |pages=349–367 |doi=10.1098/rsta.1987.0091 |bibcode=1987RSPTA.323..349H |last1=Hughes |first1=D. W. }}</ref>
* '''1761'''&nbsp;– [[Mikhail Lomonosov]] is the first to discover and appreciate the [[atmosphere of Venus]] during his observation of the transit of Venus.<ref>{{cite journal |title=The 1761 Discovery of Venus' Atmosphere: Lomonosov and Others |journal=[[Journal of Astronomical History and Heritage]] |first=Vladimir |last=Shiltsev |volume=17 |issue=1 |pages=85–112 |date=March 2014 |doi=10.3724/SP.J.1440-2807.2014.01.06 |bibcode=2014JAHH...17...85S }}</ref>
* '''1766'''&nbsp;– [[Johann Titius]] finds the [[Titius-Bode]] rule for planetary distances.<ref name="hoskin">{{cite web |last=Hoskin |first=Michael |date=1992-06-26 |title=Bodes' law and the discovery of Ceres |publisher=Observatorio Astronomico di Palermo 'Giuseppe S. Vaiana' |url=http://www.astropa.unipa.it/HISTORY/hoskin.html |access-date=2007-07-05}}</ref>
* '''1772'''&nbsp;– [[Johann Bode]] publishes the Titius-Bode rule for planetary distances.<ref name="hoskin" />
* '''1772–1775'''&nbsp;– The [[second voyage of James Cook]] definitively disproves the existence of the hypothesized Southern continent of [[Terra Australis]].<ref>{{cite book |title=Captain James Cook |first=Richard |last=Hough |year=1994 | publisher=Hodder and Stoughton |pages=239| isbn =0-340-82556-1 }}</ref>
* '''1775'''&nbsp;– [[Charles Hutton]], based on his analysis of the [[Schiehallion experiment]], shows the Earth has a density of at least {{nowrap|4,500 kg·m<sup>−3</sup>}} and suggests that it has a [[planetary core]] made of metal. (In comparison with the modern accepted figure of {{nowrap|5,515 kg·m<sup>−3</sup>}}, the density of the Earth had been computed with an error of less than 20%.)<ref>{{Cite book|last=Danson|first=Edwin |title=Weighing the World |publisher=Oxford University Press|date=2006|pages=153–154|isbn=978-0-19-518169-2|url=https://books.google.com/books?id=UNH_Y7ERFeoC&pg=PA153}}</ref>
* '''1781'''&nbsp;– [[William Herschel]] discovers a seventh planet, [[Uranus]], during a telescopic survey of the Northern sky.<ref>{{cite book |author=Dreyer, J. L. E. |date=1912 |title=The Scientific Papers of Sir William Herschel. Vol. 1|publisher=Royal Society and Royal Astronomical Society |pages=100 |isbn=978-1-84371-022-6 }}</ref>[[File:Lossy-page1-3705px-Herschel's Grand Forty feet Reflecting Telescopes RMG F8607 (cropped).jpg|thumb|upright|The William Herschel's [[40-foot telescope|40-foot (12 m) telescope]]]]
* '''1781'''&nbsp;– [[Charles Messier]] and his assistant [[Pierre Méchain]] publish the [[Messier object|first catalogue]] of 110 [[nebulae]] and [[star clusters]], the most prominent [[deep-sky object]]s that can easily be observed from Earth's [[Northern Hemisphere]], in order not to be confused with ordinary Solar System's [[comet]]s.<ref>{{cite web |title=Original Messier Catalog of 1781 |website=[[Students for the Exploration and Development of Space]] |date=10 November 2007 |url=http://messier.seds.org/xtra/Mcat/mcat1781.html#messier1781}}</ref>
* '''1787'''&nbsp;– Herschel discovers Uranus's moons [[Titania (moon)|Titania]] and [[Oberon (moon)|Oberon]].<ref>{{cite journal |doi=10.1098/rstl.1787.0016| last=Herschel |first=W. S.|title=An Account of the Discovery of Two Satellites Revolving Round the Georgian Planet |journal=Philosophical Transactions of the Royal Society of London |volume=77 |pages=125–129 |year=1787| jstor=106717 |doi-access=free}}</ref>
* '''1789'''&nbsp;– Herschel discovers Saturn's moons [[Enceladus (moon)|Enceladus]] and [[Mimas (moon)|Mimas]].<ref>{{cite web|url=http://planetarynames.wr.usgs.gov/append7.html|title=Planetary Body Names and Discoverers|work=Gazetteer of Planetary Nomenclature|publisher=[[Astrogeology Research Program|USGS Astrogeology Science Center]]|access-date=January 12, 2015|archive-date=August 25, 2009|archive-url=https://web.archive.org/web/20090825153846/http://planetarynames.wr.usgs.gov/append7.html|url-status=live}}</ref>
* '''1796'''&nbsp;– [[Pierre Laplace]] re-states the nebular hypothesis for the formation of the Solar System from a spinning [[nebula]] of gas and dust.<ref>Owen, T. C. (2001) "Solar system: origin of the solar system", ''[[Encyclopædia Britannica]]'', Deluxe CDROM edition</ref>
* '''1798'''&nbsp;– [[Henry Cavendish]] accurately [[Cavendish experiment|measures the gravitational constant in the laboratory]], which allows the mass of the Earth to be derived, and hence the masses of all bodies in the Solar System.<ref>{{cite book | last=Poynting | first=John H. | title=The Mean Density of the Earth: An essay to which the Adams prize was adjudged in 1893 | year=1894 | publisher=C. Griffin & Co. | location=London | url=https://archive.org/details/meandensityeart00poyngoog }}</ref>

==19th century==
* '''1801'''&nbsp;– [[Giuseppe Piazzi]] discovers [[Ceres (dwarf planet)|Ceres]], a body that filled a gap between Mars and Jupiter following the [[Titius-Bode]] rule. At first, it was regarded as a new planet.<ref>{{Cite web |last=Landau |first=Elizabeth |date=26 January 2016 |title=Ceres: Keeping Well-Guarded Secrets for 215 Years |url=http://www.jpl.nasa.gov/news/news.php?feature=4824 |url-status=live |archive-url=https://web.archive.org/web/20190524043553/https://www.jpl.nasa.gov/news/news.php?feature=4824 |archive-date=24 May 2019 |access-date=26 January 2016 |website=NASA}}</ref>
* '''1802'''&nbsp;– [[Heinrich Wilhelm Olbers]] discovers [[2 Pallas|Pallas]], at roughly the same distance to the Sun than Ceres.<ref>{{cite web | url = http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_06.asp | title = Astronomical Serendipity | publisher = NASA JPL | access-date = 15 March 2007 | url-status = dead | archive-url = https://web.archive.org/web/20120206235537/http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_06.asp | archive-date = 6 February 2012 }}</ref> He proposed that the two objects were the remnants of a [[Phaeton (hypothetical planet)|destroyed planet]],<ref name="ARX-20060816">{{cite journal |last=Soter |first=Steven |title=What is a Planet? |date=2006 |journal= The Astronomical Journal|volume=132 |issue=6 |pages=2513–2519 |arxiv=astro-ph/0608359 |doi=10.1086/508861 |bibcode=2006AJ....132.2513S }}</ref> and predicted that more of these pieces would be found.
* '''1802'''&nbsp;– Due their star-like apparience, William Herschel suggested Ceres and Pallas, and similar objects if found, be placed into a separate category, named [[asteroid]]s, although they were still counted among the planets for some decades.<ref>{{cite journal |title=William Herschel and the First Two Asteroids |author=Cunningham, Clifford |place=Dance Hall Observatory, Ontario |date=1984 |bibcode=1984MPBu...11....3C |volume=11 |page=3 |journal=The Minor Planet Bulletin}}</ref>
* '''1804'''&nbsp;– [[Karl Ludwig Harding]] discovers the asteroid [[3 Juno|Juno]].<ref>{{cite web |type=2017-11-26 last obs |title=JPL Small-Body Database Browser: 3 Juno |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3 |access-date=2014-11-17}}</ref>
* '''1807'''&nbsp;– Olbers discovers the asteroid [[4 Vesta|Vesta]].<ref>{{cite journal | title=The discovery of Vesta | date=February 1907 | author=Lynn, W. T. | bibcode=1907Obs....30..103L | journal=The Observatory | volume=30 | pages=103–105}}</ref>
* '''1821'''&nbsp;– [[Alexis Bouvard]] detects irregularities in the [[orbit]] of Uranus.<ref>{{cite book |author=Alexander, A. F. O'D. |editor=Charles Coulston Gillespie|date=1970 |title=Dictionary of Scientific Biography|volume=2|pages=359–360|place=New York|publisher=Charles Scribner's Sons|quote="Bouvard, Alexis"}}</ref>
* '''1825'''&nbsp;– Pierre Laplace completes his study of [[gravitation]], the [[stability of the Solar System]], tides, the precession of the equinoxes, the [[libration]] of the Moon, and Saturn's rings in his work ''[[Traité de mécanique céleste]]'' (''Treatise of celestial mechanics'').<ref>{{cite book|author=Pierre-Simon, marquis de Laplace|title=Traité de mécanique céleste|date=1798–1825|url=http://catalog.hathitrust.org/Record/100242426}}</ref>
* '''1833'''&nbsp;– [[Thomas Henderson (astronomer)|Thomas Henderson]] successfully measures the [[stellar parallax]] of [[alpha Centauri]], being then regarded as the Sun's closest star, but delayed the publication until 1839.<ref name=Henderson1839>{{Cite journal|last=Henderson|first=Thomas|date=1839|title=On the Parallax of α Centauri|journal=Monthly Notices of the Royal Astronomical Society|volume=4|issue=19 |pages=168–170|doi=10.1093/mnras/4.19.168 |bibcode=1839MNRAS...4..168H|doi-access=free}}</ref>
* '''1838'''&nbsp;– [[Friedrich Wilhelm Bessel]] measures the parallax of the star [[61 Cygni]], refuting one of the oldest arguments against [[heliocentrism]].<ref>{{Cite journal| doi = 10.1093/mnras/4.17.152| last = Bessel | first = F. W. | author-link = Friedrich Bessel| title = On the parallax of 61 Cygni| journal = Monthly Notices of the Royal Astronomical Society| volume = 4| issue = 17| pages = 152–161| year = 1838b| bibcode = 1838MNRAS...4..152B| doi-access = free}}</ref>
[[File:John W Draper-The first Moon Photograph 1840.jpg|thumb|200px|The earliest surviving dagerrotype of the Moon by Draper (1840)]]
[[File:Percival Lowell observing Venus from the Lowell Observatory in 1914.jpg|thumb|200px|upright|right|Percival Lowell in 1914, observing Venus in the daytime with the {{convert|24|in|cm|adj=on}} Alvan Clark & Sons refracting telescope at Flagstaff, Arizona]]
* '''1840'''&nbsp;– [[John W. Draper]] takes a [[daguerreotype]] of the Moon, the first [[Astrophotography|astronomical photograph]].<ref>{{cite journal|last1=Kalfus|first1=Skye|title=Across the Spectrum|url=https://www.sciencehistory.org/distillations/magazine/across-the-spectrum|journal=Chemical Heritage Magazine|publisher=[[Chemical Heritage Foundation]]|date= 2010|volume=28|issue=2|access-date=23 March 2018}}</ref>
* '''1845'''&nbsp;– [[John Couch Adams|John Adams]] predicts the existence and location of an eighth planet from irregularities in the orbit of Uranus.<ref name="ChronologyOnUranus">{{cite web | author=Kollerstrom, N. | year=2001 | url=http://www.ucl.ac.uk/sts/nk/neptune/chron.htm | title=A Neptune Discovery Chronology | work=The British Case for Co-prediction | publisher=University College London | access-date=2007-08-23 | archive-url=https://web.archive.org/web/20051119031753/http://www.ucl.ac.uk/sts/nk/neptune/chron.htm | archive-date=2005-11-19 }}</ref>
* '''1845'''&nbsp;– [[Karl Ludwig Hencke]] discovers a fifth body between Mars and Jupiter, [[5 Astraea|Astraea]]<ref name="Encyclopedia-of-Astronomers">{{cite book |title=The Biographical Encyclopedia of Astronomers |last=Hockey |first=Thomas |date=2009 |publisher=[[Springer Publishing]]|isbn= 978-0-387-31022-0 |url=http://www.springerreference.com/docs/html/chapterdbid/58599.html |access-date=22 August 2012}}</ref> and, shortly thereafter, new objects were found there at an accelerating rate. Counting them among the planets became increasingly cumbersome. Eventually, they were dropped from the planet list (as first suggested by [[Alexander von Humboldt]] in the early 1850s) and Herschel's coinage, "asteroids", gradually came into common use.<ref name="asteroids">{{cite web|title=When Did the Asteroids Become Minor Planets?|author=Hilton, J.|work=US Naval Observatory (USNO)|date=2001|url=http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/minor-planets|access-date=2007-10-01|url-status=dead|archive-url=https://web.archive.org/web/20120406222551/http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/minor-planets/|archive-date=2012-04-06}}</ref> Since then, the region they occupy between Mars and Jupiter is known as the [[asteroid belt]].
* '''1846'''&nbsp;– [[Urbain Le Verrier]] predicts the existence and location of an eighth planet from irregularities in the orbit of Uranus.<ref name="ChronologyOnUranus" />
* '''1846'''&nbsp;– [[Johann Galle]] [[Discovery of Neptune|discovers]] the eighth planet, [[Neptune]], following the predicted position gave to him by Le Verrier.<ref name="ChronologyOnUranus" />
* '''1846'''&nbsp;– [[William Lassell]] discovers Neptune's moon [[Triton (moon)|Triton]], just seventeen days later of planet's discovery.<ref>{{cite journal |last=Lassell |first=W. |title= Discovery of supposed ring and satellite of Neptune|year=1846 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=7 |issue=9 | page=157 |bibcode=1846MNRAS...7..157L |doi=10.1093/mnras/7.9.154 |doi-access=free }}</ref>
* '''1848'''&nbsp;– Lassell, [[William Cranch Bond]] and [[George Phillips Bond]] discover Saturn's moon [[Hyperion (moon)|Hyperion]].<ref>{{cite journal |author=W. Lassell |date=1848 |title=Discovery of a New Satellite of Saturn |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=8 |issue=9 |pages=195–197 |doi=10.1093/mnras/8.9.195a |bibcode=1848MNRAS...8..195L |url=https://zenodo.org/record/1431913 |doi-access=free }}</ref><ref>{{cite journal |first=W.C. |last=Bond |date=1848 |title=Discovery of a new satellite of Saturn |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=9 |issue=1 |pages=1–2 |doi=10.1093/mnras/9.1.1 |bibcode=1848MNRAS...9....1B |url=https://zenodo.org/record/1431915 |doi-access=free }}</ref>
* '''1849'''&nbsp;– [[Édouard Roche]] finds the limiting radius of [[tide|tidal]] destruction and tidal creation for a body held together only by its own gravity, called the [[Roche limit]], and uses it to explain why Saturn's rings do not condense into a satellite.<ref name="two">{{Cite web |url=http://saturn.jpl.nasa.gov/faq/FAQSaturn/#q11 |archive-url=https://web.archive.org/web/20090423160619/http://saturn.jpl.nasa.gov/faq/FAQSaturn/#q11 |url-status=dead |archive-date=April 23, 2009 |title=What is the Roche limit? |access-date=September 5, 2007 |publisher=NASA&nbsp;– JPL |author=NASA}}</ref>
* '''1849'''&nbsp;– [[Annibale de Gasparis]] discovers the asteroid [[10 Hygiea|Hygiea]], the fourth largest asteroid in the Solar System by both volume and mass.<ref>{{cite journal |title=Comparison of Theory with Observation for the Minor planets 10 Hygiea and 175 Andromache with Respect to Perturbations by Jupiter |last=Leuschner |first=A. O. |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=8 |issue=7 |date=1922-07-15 |pages=170–173 |doi=10.1073/pnas.8.7.170 |pmid=16586868 |pmc=1085085 |bibcode = 1922PNAS....8..170L|doi-access=free }}</ref>
* '''1851'''&nbsp;– Lassell discovers Uranus's moons [[Ariel (moon)|Ariel]] and [[Umbriel]].<ref>{{cite journal| last=Lassell| first=W. |date=1851| title=On the interior satellites of Uranus |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=12| pages=15–17 |bibcode=1851MNRAS..12...15L |doi=10.1093/mnras/12.1.15 |doi-access=free}}</ref>
* '''1856'''&nbsp;– [[James Clerk Maxwell]] demonstrates that a solid ring around Saturn would be torn apart by gravitational forces and argues that Saturn's rings consist of a multitude of tiny satellites.<ref>{{cite ODNB |author=Harman, Peter M. |date=2004 |quote="Maxwell, James"|title=[[Oxford Dictionary of National Biography]] (online ed.)|pages=508 |doi=10.1093/ref:odnb/5624}}</ref>
* '''1859'''&nbsp;– [[Robert Bunsen]] and [[Gustav Kirchhoff]] develop the [[History of spectroscopy|spectroscope]], which they used to pioneer the identification of the [[chemical element]]s in the Sun,<ref>{{Cite EB1911|wstitle=Kirchhoff, Gustav Robert |short=x |noicon=x|quote=[...] to him belongs the merit of having [...] enunciated a complete account of its theory, and of thus having firmly established it as a means by which the chemical constituents of celestial bodies can be discovered through the comparison of their spectra with those of the various elements that exist on this earth.}}</ref> showing that the Sun contains mainly [[hydrogen]], and also [[sodium]].
* '''1862'''&nbsp;– By analysing the [[spectroscopic]] signature of the Sun and comparing it to those of other stars, Father [[Angelo Secchi]] determines that the Sun is itself a star.<ref>{{CathEncy|wstitle=Angelo Secchi|first= J.|last= Pohle |quote=[...][his] theory of the unity of the world and of the identity of the fixed stars and the sun received most profound scientific demonstration and confirmation.}}</ref>
* '''1866'''&nbsp;– [[Giovanni Schiaparelli]] realizes that [[meteor]] streams occur when the Earth passes through the orbit of a comet that has left debris along its path.<ref>{{cite book |title=Dictionary of Minor Planet Names – (4062) Schiaparelli |last=Schmadel |first=Lutz D.|publisher=Springer Berlin Heidelberg |page=347 |date=2007 |isbn=978-3-540-00238-3 |doi=10.1007/978-3-540-29925-7_4041 |chapter=(4062) Schiaparelli }}</ref>
* '''1868'''&nbsp;– [[Jules Janssen]] observes a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the [[chromosphere]] of the Sun, during a total solar eclipse in Guntur, India. Later in the same year, [[Norman Lockyer]] observed the same line in the solar spectrum, and concluded that it was caused by an element in the Sun unknown on Earth. This element is [[helium]], which currently comprises 23.8% of the mass in the solar [[photosphere]].<ref>{{cite journal |author=Thomson, William |date=August 3, 1871 |title=Inaugural Address of Sir William Thomson| journal=Nature |volume=4 |issue=92 |pages=261–278 [268] |bibcode=1871Natur...4..261. |doi=10.1038/004261a0 |pmc=2070380 |url=https://books.google.com/books?id=IogCAAAAIAAJ&pg=PA268 |quote=Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium}}</ref>
* '''1877'''&nbsp;– [[Asaph Hall]] discovers Mars's moons [[Deimos (moon)|Deimos]] and [[Phobos (moon)|Phobos]].<ref>{{cite journal|bibcode=1877AN.....91...11H|title=Observations of the Satellites of Mars|last1=Hall|first1=Asaph|journal=Astronomische Nachrichten|volume=91|issue=1|pages=11–14|year=1877|doi=10.1002/asna.18780910103|url=https://zenodo.org/record/1424707|access-date=1 July 2021|archive-date=1 October 2021|archive-url=https://web.archive.org/web/20211001044436/https://zenodo.org/record/1424707|url-status=live}}</ref>
* '''1887'''&nbsp;– The [[Michelson–Morley experiment]], intended to measure the [[relative motion]] of Earth through the (assumed) stationary [[luminiferous aether]], got no results. This put an end to the centuries-old idea of the [[Aether (classical element)|aether]], dating back to [[Aristotle]], and with it all the contemporary [[aether theories]].<ref>{{cite journal |last1=Michelson |first1=Albert A. |last2=Morley |first2=Edward W.|title=On the Relative Motion of the Earth and the Luminiferous Ether |journal=American Journal of Science |volume=34 |issue=203 |year=1887 |pages=333–345 |doi=10.2475/ajs.s3-34.203.333|title-link=s:On the Relative Motion of the Earth and the Luminiferous Ether |bibcode=1887AmJS...34..333M }}</ref>
* '''1892'''&nbsp;– [[Edward Emerson Barnard]] discovers Jupiter's moon [[Amalthea (moon)|Amalthea]].<ref>{{cite journal| doi = 10.1086/101715| last = Barnard| first = E. E.| date = 12 October 1892| title = Discovery and observations of a fifth satellite to Jupiter| journal = The Astronomical Journal| volume = 12| issue = 11| pages = 81–85| bibcode = 1892AJ.....12...81B}}</ref>
* '''1895'''&nbsp;– [[Percival Lowell]] starts publishing books about his observations of features in the surface on Mars that he claimed as artificial [[Martian canals]] (due to a mistranslation of a previous paper by Schiaparelli on the subject), popularizing the long-held belief that these markings showed that Mars harbors [[Life on Mars|intelligent life forms]].<ref>{{cite book |author=Kidger, Mark |date=2005 |title=Astronomical Enigmas: Life on Mars, the Star of Bethlehem, and Other Milky Way Mysteries |pages=110 |publisher=JHU Press |isbn=0801880262}}</ref>
* '''1897'''&nbsp;– [[William Thomson, 1st Baron Kelvin]], based on the thermal radiation rate and the [[Kelvin–Helmholtz mechanism|gravitational contraction]] forces, argues the age of the Sun to be no more than 20 million years – unless some energy source beyond what was then known was found.<ref>{{cite magazine |last1=Thomson |first1=William |year=1862 |title=On the Age of the Sun's Heat |url=https://zapatopi.net/kelvin/papers/on_the_age_of_the_suns_heat.html |magazine=Macmillan's Magazine |volume=5 |pages=388–393}}</ref>
* '''1899'''&nbsp;– [[William Henry Pickering]] discovers Saturn's moon [[Phoebe (moon)|Phoebe]].<ref>{{cite journal |last1=Pickering |first1=E. C. |title=A New Satellite of Saturn |journal=Science |date=24 March 1899 |volume=9 |issue=221 |pages=456 |doi=10.1126/science.9.221.456 |pmid=17844472 }}</ref>

==1900–1957==
[[File:Palomar Mountain Observatory 3c 1948 issue U.S. stamp.jpg|thumb|[[Palomar Mountain Observatory]] featured on 1948 United States stamp]]
* '''1904'''&nbsp;– [[Ernest Rutherford]] argues, in a lecture attended by Kelvin, that [[radioactive decay]] releases heat, providing the unknown energy source Kelvin had suggested, and ultimately leading to [[radiometric dating]] of rocks which reveals ages of billions of years for the Solar System bodies.<ref>{{cite magazine |author1=England, P. |author2=Molnar, P. |author3=Righter, F. |date=January 2007 |title=John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics |magazine=GSA Today |volume=17 |issue=1 |pages=4–9 |doi=10.1130/GSAT01701A.1}}</ref>
* '''1906'''&nbsp;– [[Max Wolf]] discovers the [[Trojan asteroid]] [[588 Achilles|Achilles]].<ref name="MPC-object">{{cite web |title=588 Achilles (1906 TG) |work=Minor Planet Center |url=https://www.minorplanetcenter.net/db_search/show_object?object_id=588 |access-date=15 June 2018}}</ref>
* '''1908'''&nbsp;– A [[meteor air burst]] [[Tunguska event|occurs near Tunguska]] in [[Siberia|Siberia, Russia]]. It is the largest [[impact event]] on Earth in recorded history to date.<ref>{{cite APOD|date=14 November 2007|title=Tunguska: The Largest Recent Impact Event|access-date=12 September 2011}}</ref>
* '''1909'''&nbsp;– [[Andrija Mohorovičić]] discovers the [[Mohorovičić discontinuity|Moho discontinuity]], the boundary between the Earth's [[Crust (geology)|crust]] and the [[Mantle (geology)|mantle]].<ref>{{cite book |last1=Braile |first1=L.W. |last2=Chiang |first2=C.S. |chapter=The Continental Mohorovičić Discontinuity: Results from Near-Vertical and Wide-Angle Seismic Reflection Studies |pages=257–272 |editor1-last=Barazangi |editor1-first=Muawia |editor2-last=Brown |editor2-first=Larry |date=1986 |title=Reflection Seismology: A Global Perspective |series=Geodynamics Series |volume=13 |isbn=978-0-87590-513-6 |doi=10.1029/GD013 }}</ref>
* '''1912'''&nbsp;– [[Alfred Wegener]] suggests the [[continental drift]] hypothesis, that the continents are slowly drifting around the Earth.<ref>{{cite journal |author=Jacoby, W. R. |date=January 1981 |title=Modern concepts of earth dynamics anticipated by Alfred Wegener in 1912 |journal=Geology |volume=9 |issue=1 |pages=25–27 |bibcode=1981Geo.....9...25J |doi=10.1130/0091-7613(1981)9<25:MCOEDA>2.0.CO;2 }}</ref>
* '''1915'''&nbsp;– [[Robert T. A. Innes|Robert Innes]] discovers [[Proxima Centauri]], the closest star to Earth after the Sun.<ref>{{cite book |last=Glass|first= I.S.|year= 2008|title= Proxima, the Nearest Star (other than the Sun)|publisher=Mons Mensa|location=Cape Town}}</ref>
* '''1919'''&nbsp;– [[Arthur Stanley Eddington]] uses a solar eclipse to successfully test [[Albert Einstein]]'s [[General Theory of Relativity]],<ref>{{cite journal|last=Dyson|author2=Eddington, A.S.|author3=Davidson, C.R. |date=1920 |title=A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Solar eclipse of May 29, 1919|journal= [[Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|Philosophical Transactions of the Royal Society A]]|volume=220|issue=571–581|pages= 291–333|bibcode=1920RSPTA.220..291D|doi=10.1098/rsta.1920.0009|first =F.W.|url=https://zenodo.org/record/1432106|doi-access=free}}</ref> which in turn explains the observed [[Apsidal precession|irregularities in the orbital motion]] of Mercury,<ref>{{Citation |last=Pais |first=Abraham |title='Subtle is the Lord&nbsp;...' The Science and life of Albert Einstein |publisher=Oxford University Press |date=1982 |pages=253–254 |isbn=978-0-19-853907-0 |url=https://archive.org/details/subtleislordscie00pais}}</ref> and disproves the existence of the hypothesized inner planet [[Vulcan (hypothetical planet)|Vulcan]].
* '''1920'''&nbsp;– In the [[Great Debate (astronomy)|Great Debate]] between [[Harlow Shapley]] and [[Heber Curtis]], [[Galaxy|galaxies]] are finally recognized as objects beyond the Milky Way, and the Milky Way as a galaxy proper.<ref>{{cite web|first=Ben |last=Evans |date=April 25, 2020|title=The Great Debate – 100 years later|url=https://astronomy.com/news/2020/04/the-great-debate-of-shapley-and-curtis--100-years-later|access-date=2020-09-10|website=Astronomy.com|language=en}}</ref> Within it lies the Solar System.
* '''1930'''&nbsp;– [[Clyde Tombaugh]] discovers [[Pluto]].<ref>{{cite journal |author=Tombaugh, Clyde W. |date=1946 |title=The Search for the Ninth Planet, Pluto |journal=Astronomical Society of the Pacific Leaflets |volume=5 |issue=209 |pages=73–80 |bibcode=1946ASPL....5...73T}}</ref> It was regarded for decades as the [[Planets beyond Neptune|ninth planet]] of the Solar System.
[[File:First photo from space.jpg|thumb|The first photo from space was taken from a V-2 launched by US scientists on 24 October 1946.]]
* '''1930'''&nbsp;– [[Seth Nicholson]] and [[Edison Pettit]] measure the surface temperature of the Moon.<ref>{{cite journal|title=Obituary: Seth B. Nicholson|journal=Physics Today|date=September 1963|volume=16|issue=9|pages=106|doi=10.1063/1.3051113|doi-access=free}}</ref>
* '''1932'''&nbsp;– [[Karl Guthe Jansky]] recognizes received [[radio signal]]s coming from [[outer space]] as extrasolar, coming mainly from [[Sagittarius (constellation)|Sagittarius]].<ref>{{cite journal |last1=Jansky |first1=K.G. |title=Electrical Disturbances Apparently of Extraterrestrial Origin |journal=Proceedings of the IRE |date=October 1933 |volume=21 |issue=10 |pages=1387–1398 |doi=10.1109/JRPROC.1933.227458 }}</ref><ref>{{cite journal |last1=Jansky |first1=Karl G. |title=Radio Waves from Outside the Solar System |journal=Nature |date=July 1933 |volume=132 |issue=3323 |pages=66 |doi=10.1038/132066a0 |bibcode=1933Natur.132...66J }}</ref> They are the first evidence of the center of the Milky Way, and the firsts experiences that founded the discipline of [[radio astronomy]].
* '''1935'''&nbsp;– The ''[[Explorer II]]'' balloon reached a record altitude of 22,066&nbsp;m (72,395&nbsp;ft), enabling its occupants to photograph the curvature of the Earth for the first time.<ref>{{citation |last1=Bilstein |first1=Roger E. |title=Flight in America: From the Wrights to the Astronauts |publisher=JHU Press |page=118 |edition=3rd |year=2001 |isbn=0801866855 |url= https://books.google.com/books?id=PKeVjYtzLr0C&pg=PA118}}</ref>
* '''1938'''&nbsp;– [[Hans Bethe]] calculates the details of the [[Hydrogen fusion|two main]] energy-producing [[nuclear reaction]]s that power the Sun.<ref>{{cite journal |last1=Bethe |first1=H. |last2=Critchfield |first2=C. |date=1938 |title=On the Formation of Deuterons by Proton Combination |journal=Physical Review |volume=54 |issue=10 |pages=862 |bibcode=1938PhRv...54Q.862B |doi=10.1103/PhysRev.54.862.2}}</ref><ref>{{cite journal |last=Bethe |first=H. |date=1939 |title=Energy Production in Stars |journal=Physical Review |volume=55 |issue=1 |pages=434–456 |bibcode=1939PhRv...55..434B |doi=10.1103/PhysRev.55.434 |pmid=17835673 |doi-access=free }}</ref>
* '''1944'''&nbsp;– [[Gerard Kuiper]] discovers that the satellite [[Titan (moon)|Titan]] has a substantial atmosphere.<ref name="OnKuiper">{{cite web |url=http://www.azarchivesonline.org/xtf/view?docId=ead/uoa/UAMS480.xml |title=Gerard Kuiper Papers |series=Archive |publisher=University of Arizona |website=AzArchivesOnline.org}}</ref>
* '''1946'''&nbsp;– American launch of a camera-equipped [[V-2 rocket]] provides the first image of the Earth from space.<ref>{{cite web|url=https://www.airspacemag.com/space/the-first-photo-from-space-13721411/|title=First Photo From Space|date=October 24, 2006|archive-url=https://web.archive.org/web/20210129004546/https://www.airspacemag.com/space/the-first-photo-from-space-13721411/|archive-date=January 29, 2021|url-status=live}}</ref>
* '''1949'''&nbsp;– Gerard Kuiper discovers Uranus's moon [[Miranda (moon)|Miranda]] and Neptune's moon [[Nereid (moon)|Nereid]].<ref name="OnKuiper" />
* '''1950'''&nbsp;– [[Jan Oort]] suggests the presence of a cometary reservoir in the outer limits of the Solar System, the [[Oort cloud]].<ref>{{cite news |last=Redd |first=Nola Taylor |title=Oort Cloud: The Outer Solar System's Icy Shell |url=https://www.space.com/16401-oort-cloud-the-outer-solar-system-s-icy-shell.html |date=October 4, 2018 |work=[[Space.com]] |access-date=August 18, 2020 |archive-date=January 26, 2021 |archive-url=https://web.archive.org/web/20210126014353/https://www.space.com/16401-oort-cloud-the-outer-solar-system-s-icy-shell.html |url-status=live }}</ref>
* '''1951'''&nbsp;– Gerard Kuiper argues for an annular reservoir of comets between 40 and 100 [[astronomical unit]]s from the Sun having formed early in the Solar System's evolution, but he did not think that such a belt still existed today.<ref name="Jewitt">{{cite web |title=WHY "KUIPER" BELT? |author=David Jewitt |work=University of Hawaii |url=http://www2.ess.ucla.edu/~jewitt/kb/gerard.html |access-date=14 June 2007}}</ref> Decades later, this region was named after him, the [[Kuiper belt]].

==1958–1976==
{{See also|Space technology|Space exploration}}
[[File:First View of Earth from Moon.jpg|thumb|Earth taken from Lunar Orbiter 1 in 1966. Image as originally shown to the public displays extensive flaws and striping.]]
[[File:Pioneer 10 at Jupiter.jpg|thumb|right|Artist's impression of ''Pioneer 10''{{'}}s flyby of Jupiter]]
* '''1958'''&nbsp;– Under supervision of [[James Van Allen]], ''[[Explorer&nbsp;1]]'' and ''[[Explorer&nbsp;3]]'' confirmed the existence of the Earth's [[magnetosphere]] [[Van Allen radiation belt|radiation belt]]s, named after him.<ref>{{cite news |url=https://news.google.com/newspapers?id=kCxQAAAAIBAJ&sjid=HVYDAAAAIBAJ&pg=3307%2C5547467 |work=Victoria Advocate |location=Texas |agency=Associated Press |title='Doughnuts' of radiation ring earth in space |date=December 28, 1958 |page=1A}}</ref>
* '''1959'''&nbsp;– ''[[Explorer 6]]'' sends the first image of the entire Earth from space.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1959-004A|title=Display: Explorer 6 1959-004A|publisher=NASA|date=28 October 2021|access-date=3 November 2021}}</ref>
* '''1959'''&nbsp;– [[Luna 3]] sends the first images of another celestial body, the Moon, from space, including its unseen [[Far side of the Moon|far side]].<ref>{{cite book | last=Harvey | first=Brian | title=Russian space probes: scientific discoveries and future missions | publisher=Springer | publication-place=New York | year=2011 | isbn=978-1-4419-8150-9 }}</ref>
* '''1962'''&nbsp;– ''[[Mariner 2]]'' Venus flyby performs the first closeup observations of another planet.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1962-041A|title=Mariner 2|publisher=US National Space Science Data Center|access-date=September 8, 2013|archive-date=April 15, 2019|archive-url=https://web.archive.org/web/20190415220330/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1962-041A|url-status=live}}</ref>
* '''1964'''&nbsp;– ''[[Mariner 4]]'' spacecraft provides the first detailed images of the surface of Mars.<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1964-077A |title=Mariner 4 |work=NSSDC Master Catalog |publisher=[[NASA]] |access-date=February 11, 2009}}</ref>
* '''1966'''&nbsp;– [[Luna 9]] Moon lander provides the first images from the surface of another celestial body.<ref name="BeyondEarth">{{cite book|url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf|title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016|pages=1–2|last1=Siddiqi|first1=Asif A.|lccn=2017059404|isbn=9781626830424|publisher=NASA History Program Office|edition=second |year=2018|id=SP2018-4041|series=The NASA history series|location=Washington, D.C.}}</ref>
* '''1967'''&nbsp;– ''[[Venera 4]]'' provides the first information on Venus's dense atmosphere.<ref>{{cite book|title=Russian planetary exploration|first1=Brian|last1=Harvey|url=https://books.google.com/books?id=jKmIclMIwPAC&pg=PA101|publisher=Springer|year=2007|isbn=978-0-387-46343-8|pages=98–101}}</ref>
* '''1968'''&nbsp;– [[Apollo 8]] becomes the first crewed lunar mission, providing historic images of the whole Earth.<ref>{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Apollo 8's Earthrise: The Shot Seen Round the World{{snd}}Half a century ago today, a photograph from the moon helped humans rediscover Earth. |url=https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-date=2022-01-01 |url-access=limited |date=December 21, 2018 |work=[[The New York Times]] |access-date=December 24, 2018 }}{{cbignore}}</ref>
* '''1969'''&nbsp;– [[Apollo 11]] mission landed on the Moon, first humans walking upon it.<ref>{{cite journal |editor=Jones, Eric M. |date=1995 |title=The First Lunar Landing |journal=Apollo 11 Lunar Surface Journal |publisher=NASA |archive-date=December 27, 2016|access-date=June 13, 2013 |archive-url=https://web.archive.org/web/20161227230604/http://www.hq.nasa.gov/alsj/a11/a11.landing.html |url-status=dead |url=http://www.hq.nasa.gov/alsj/a11/a11.landing.html}}</ref> They return the first [[Moon rock|lunar samples]] back to Earth.<ref>{{cite web|url=https://curator.jsc.nasa.gov/lunar/lun-fac.cfm |title=NASA Lunar Sample Laboratory Facility |date=1 September 2016 |website=NASA Curation Lunar |publisher=[[NASA]] |access-date=13 October 2018 |url-status=live |archive-url=https://web.archive.org/web/20180825074518/https://curator.jsc.nasa.gov/lunar/lun-fac.cfm |archive-date=25 August 2018}}</ref>
* '''1970'''&nbsp;– ''[[Venera 7]]'' Venus lander sends back the first information successfully obtained from the surface of another planet.<ref>{{cite magazine|url=http://www.time.com/time/magazine/article/0,9171,909834,00.html|archive-url=https://web.archive.org/web/20081221214000/http://www.time.com/time/magazine/article/0,9171,909834,00.html|url-status=dead|archive-date=21 December 2008|magazine=[[Time (magazine)|Time]]|date=8 February 1971|access-date=2 January 2013|title=Science: Onward from Venus}}</ref>
* '''1971'''&nbsp;– ''[[Mariner 9]]'' Mars spacecraft becomes the first to successfully orbit another planet.<ref>{{cite web | url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1971-051A | title=Mariner 9: Details | publisher=National Space Science Data Center | access-date=December 28, 2011}}</ref> It provides the first detailed maps of the Martian surface,<ref>{{Cite web |url=http://mars.jpl.nasa.gov/programmissions/missions/log/ |title=NASA Programs & Missions Historical Log |access-date=2011-12-12 |archive-url=https://web.archive.org/web/20141113205319/http://mars.jpl.nasa.gov/programmissions/missions/log/ |archive-date=2014-11-13 |url-status=dead }}</ref> discovering much of the planet's topography, including the volcano [[Olympus Mons]] and the canyon system [[Valles Marineris]], which is named in its honor.
* '''1971'''&nbsp;– ''[[Mars 3]]'' lands on Mars, and transmits the first partial image from the surface of another planet.<ref>{{cite book|last=Perminov|first=V.G.|title=The Difficult Road to Mars – A Brief History of Mars Exploration in the Soviet Union|date=July 1999|publisher=NASA Headquarters History Division|isbn=0-16-058859-6|pages=[https://archive.org/details/difficultroadtom00perm/page/34 34–60]|url=https://archive.org/details/difficultroadtom00perm/page/34}}</ref>
* '''1973'''&nbsp;– [[Skylab]] astronauts discover the Sun's [[coronal holes]].<ref>{{cite web|title=Massive Coronal Hole on the Sun|url=http://www.nasa.gov/mission_pages/sunearth/news/gallery/20130618-coronalhole.html|website=NASA|date=24 June 2013 |access-date=31 October 2014}}</ref>
* '''1973'''&nbsp;– ''[[Pioneer 10]]'' flies by Jupiter, providing the first closeup images of the planet and revealing its intense radiation belts.<ref>{{cite book |title=SP-349/396 Pioneer Odyssey  |last=Fimmel |first=R. O. |author2=W. Swindell|author3=E. Burgess |date=1974 |publisher=NASA-Ames Research Center |id=SP-349/396|url=https://history.nasa.gov/SP-349/ch8.htm |access-date=January 9, 2011}}</ref>
* '''1973'''&nbsp;– ''[[Mariner 10]]'' provides the first closeup images of the clouds of Venus.<ref name="BeyondEarth" />
* '''1974'''&nbsp;– ''Mariner 10'' provides the first closeup images of the surface of Mercury.<ref name="BeyondEarth" />
* '''1975'''&nbsp;– ''[[Venera 9]]'' becomes the first probe to successfully transmit images from the surface of Venus.<ref>{{cite web|url=http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=3563|title=Solar System Exploration Multimedia Gallery: Venera 9|archive-url=https://web.archive.org/web/20090803180528/http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=3563|archive-date=August 3, 2009|website=NASA|url-status=dead|access-date=August 7, 2009}}</ref>
* '''1976'''&nbsp;– [[Viking program|''Viking 1'' and ''2'']] become the first probes to send images (in color) from the surface of Mars, as well as to perform ''in situ'' [[Viking spacecraft biological experiments|biological experiments with the Martian soil]].<ref name="NASA-20061218">{{cite web |last=Williams |first=David R. Dr. |title=Viking Mission to Mars |url=https://nssdc.gsfc.nasa.gov/planetary/viking.html |date=December 18, 2006 |work=[[NASA]] |access-date=February 2, 2014 }}</ref>

==1977–2000==
[[File:Venus map with labels.jpg|thumb|right|200px|A map of Venus produced from ''Pioneer'' data]]
* '''1977'''&nbsp;– [[James L. Elliot|James Elliot]] discovers the [[rings of Uranus]] during a stellar occultation experiment on the [[Kuiper Airborne Observatory]].<ref>{{cite journal |last1=Elliot |first1=J. L. |last2=Dunham |first2=E. |last3=Mink |first3=D. |date=May 1977 |title=The rings of Uranus |journal=Nature |volume=267 |issue=5609 |pages=328–330 |bibcode=1977Natur.267..328E |doi=10.1038/267328a0 }}</ref>
* '''1977'''&nbsp;– [[Charles Kowal]] discovers [[2060 Chiron|Chiron]], the first [[Centaur (minor planet)|centaur]].<ref>{{cite journal |first1=Charles T. |last1=Kowal |first2=William |last2=Liller |first3=Brian G. |last3=Marsden |date=December 1978 |title=The discovery and orbit of /2060/ Chiron |journal=In: Dynamics of the Solar System; Proceedings of the Symposium, Tokyo, Japan, May 23–26, 1978 |volume=81 |pages=245–250 |bibcode=1979IAUS...81..245K}}</ref>
* '''1978'''&nbsp;– [[James Christy]] discovers [[Charon (moon)|Charon]], the large moon of Pluto.<ref>{{cite book|title=Planets Beyond: Discovering the Outer Solar System|first=Mark|last=Littmann|date=1990|pages=173–177, including the essay "A Moment of Perception" by James W. Christy}}</ref>
* '''1978'''&nbsp;– The ''[[Pioneer Venus]]'' probe maps the surface of Venus.<ref name="pv1">{{cite web | url=http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Venus&MCode=Pioneer_Venus_01&Display=ReadMore | title=Pioneer Venus 1 | publisher=NASA | work=Solar System Exploration | url-status=dead | archive-date=2006-10-04 | archive-url=https://web.archive.org/web/20061004114707/http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Venus&MCode=Pioneer_Venus_01&Display=ReadMore | access-date=2013-08-16 }}</ref>
* '''1978'''&nbsp;– [[Peter Goldreich]] and [[Scott Tremaine]] present a [[Boltzmann equation]] model of planetary-ring dynamics for indestructible spherical ring particles that do not self-gravitate, and they find a stability requirement relation between ring optical depth and particle normal restitution coefficient.<ref>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/0019103578901641|title=The velocity dispersion in Satun's rings|date=1978 |doi=10.1016/0019-1035(78)90164-1 |last1=Goldreich |first1=Peter |last2=Tremaine |first2=Scott |journal=Icarus |volume=34 |issue=2 |pages=227–239 |bibcode=1978Icar...34..227G |url-access=subscription }}</ref>
* '''1979'''&nbsp;– ''[[Pioneer 11]]'' flies by Saturn, providing the first ever closeup images of the planet and its rings. It discovers the planet's [[Rings of Saturn#F Ring|F ring]] and determines that its moon [[Titan (moon)|Titan]] has a thick atmosphere.<ref>{{cite book |author=Richard O. Fimmel |date=1980 |title=Pioneer: First to Jupiter, Saturn, and beyond |publisher=NASA (SP-446)}}</ref>
* '''1979'''&nbsp;– Goldreich and Tremaine postulate that Saturn's F ring is maintained by [[shepherd moon]]s, a prediction that would be confirmed by observations.<ref>{{cite web|url=http://www.solarviews.com/eng/saturnbg.htm |title=Historical Background of Saturn's Rings}}</ref>
* '''1979'''&nbsp;– ''[[Voyager 1]]'' flies by Jupiter and discovers its faint [[Rings of Jupiter|ring system]], as well as [[Volcanology of Io|volcanoes on Io]], the innermost of its [[Galilean moons]].<ref>{{cite web |url=https://voyager.jpl.nasa.gov/science/jupiter.html |title=Encounter with Jupiter |publisher=NASA |access-date=August 18, 2013}}</ref>
* '''1979'''&nbsp;– ''[[Voyager 2]]'' flies by Jupiter and discovers evidence of an ocean under the surface of its moon [[Europa (moon)|Europa]].<ref name="Voyager2">National Aeronautics and Space Administration [https://solarsystem.nasa.gov/missions/voyager-2/in-depth/ "Voyager 2"] NASA Science: Solar System Exploration. Updated January 26, 2018. Accessed December 12, 2018.</ref>
* '''1980'''&nbsp;– ''Voyager 1'' flies by Saturn and takes the first images of Titan.<ref>{{cite web |url=https://voyager.jpl.nasa.gov/science/saturn.html |title=Encounter with Saturn |publisher=NASA |access-date=August 29, 2013}}</ref> However, its atmosphere is opaque to visible light, so its surface remains obscured.
* '''1982'''&nbsp;– ''[[Venera 13]]'' lands on Venus, sends the first photographs in color of its surface, and records atmospheric wind noises, the first sounds heard from another planet.<ref>{{cite web |title=NSSDC Master Catalog – Venera 13 Descent Craft |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1981-106D |publisher=NASA National Space Science Data Center |access-date=13 April 2013}}</ref>
* '''1986'''&nbsp;– ''Voyager 2'' provides the first ever detailed images of [[Uranus]], its moons and rings.<ref name="Voyager2" />
* '''1986'''&nbsp;– The ''[[Giotto probe|Giotto]]'' probe, part of an international effort known as the "[[Halley Armada]]", provides the first ever close up images of a comet, the [[Halley's Comet]].<ref>{{cite web|title=NSSDCA Master Catalog – Giotto – Trajectory Details|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1985-056A|website=nssdc.gsfc.nasa.gov|publisher=[[NASA]]|access-date=21 June 2016}}</ref>
* '''1988'''&nbsp;– Martin Duncan, Thomas Quinn, and Scott Tremaine demonstrate that short-period comets come primarily from the Kuiper Belt and not the Oort cloud.<ref>{{cite web| url = http://discovermagazine.com/1995/nov/wherecometscomef583 |title=Where Comets Come From |work=Discovery Magazine |access-date=9 April 2007}}</ref>
* '''1989'''&nbsp;– ''Voyager 2'' provides the first ever detailed images of [[Neptune]], its moons and rings.<ref name="Voyager2" />
* '''1990'''&nbsp;– The [[Hubble Space Telescope]] is launched.<ref>{{cite web |url=http://science.ksc.nasa.gov/shuttle/missions/sts-31/mission-sts-31.html |title=STS-31 |publisher=NASA |access-date=April 26, 2008 |archive-date=August 15, 2011 |archive-url=https://web.archive.org/web/20110815191242/http://science.ksc.nasa.gov/shuttle/missions/sts-31/mission-sts-31.html |url-status=live }}</ref> Aimed primarily at deep-space objects, it is also used to observe faint objects in the Solar System.<ref>{{Cite APOD|date=March 11, 1996|title=Hubble Telescope Maps Pluto|access-date=April 26, 2008}}</ref><ref>{{cite web |url=http://www.nasaspaceflight.com/2014/06/hubble-recruited-new-horizons-pluto-target/ |title=Hubble recruited to find New Horizons probe post-Pluto target |work=nasaspaceflight.com |date=June 16, 2014 |access-date=February 1, 2020 |archive-date=June 21, 2019 |archive-url=https://web.archive.org/web/20190621093812/https://www.nasaspaceflight.com/2014/06/hubble-recruited-new-horizons-pluto-target/ |url-status=live }}</ref><ref>{{cite web |date=March 12, 2015 |title=NASA's Hubble Observations Suggest Underground Ocean on Jupiter's Largest Moon |url=http://hubblesite.org/contents/news-releases/2015/news-2015-09 |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |language=en |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150224/https://hubblesite.org/contents/news-releases/2015/news-2015-09.html |url-status=live }}</ref><ref>{{Cite web |last=Jewitt |first=David |date=April 12, 2022 |title=Hubble Confirms Largest Comet Nucleus Ever Seen |url=https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen |url-status=live |access-date=April 13, 2022 |website=NASA.GOV |archive-url=https://web.archive.org/web/20220414102506/https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen/ |archive-date=April 14, 2022 }}</ref>
* '''1990'''&nbsp;– ''Voyager 1'' is turned around to take the ''[[Portrait of the Planets]]'' of the Solar System,<ref>{{cite web |url=http://www.planetary.org/multimedia/space-images/charts/solar-system-family-portrait.html |title=The Solar System Family Portrait |access-date=November 21, 2022 |publisher=Planetary.org}}</ref> source of the ''[[Pale Blue Dot]]'' image of the Earth.<ref name=planet-soc>{{cite web|url=http://www.planetary.org/explore/space-topics/earth/pale-blue-dot.html|title=A Pale Blue Dot|publisher=The Planetary Society|access-date=December 21, 2014|url-status=live|archive-url=https://web.archive.org/web/20141219181905/http://www.planetary.org/explore/space-topics/earth/pale-blue-dot.html|archive-date=December 19, 2014}}</ref>
* '''1991'''&nbsp;– The ''[[Magellan probe|Magellan]]'' spacecraft maps the surface of Venus.<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1989-033B |title= Magellan |publisher= NASA / National Space Science Data Center |access-date=February 21, 2011}}</ref>
* '''1991'''&nbsp;– The ''[[Galileo project|Galileo]]'', while en route to Jupiter, encounters asteroid [[951 Gaspra|Gaspra]], which became the first asteroid imaged by a spacecraft.<ref name="GalileoProject">{{cite book |last=Meltzer |first=Michael |title=Mission to Jupiter: A History of the ''Galileo'' Project |year=2007 |id=SP-4231 |series=The NASA History Series |publisher=NASA |oclc=124150579 |url=https://history.nasa.gov/sp4231.pdf |access-date=19 January 2021}}</ref>
* '''1992'''&nbsp;– [[David Jewitt]] and [[Jane Luu]] of the [[University of Hawaii]] discover [[15760 Albion|Albion]], the first object deemed to be a member of the [[Kuiper belt]].<ref>{{cite web |title=15760 Albion (1992 QB1) |work=Minor Planet Center |url=https://www.minorplanetcenter.net/db_search/show_object?object_id=15760 |access-date=6 February 2018}}</ref>
* '''1993'''&nbsp;– Asteroid [[243 Ida|Ida]] is visited by the ''Galileo'' before heading to Jupiter. Mission member Ann Harch discovers its natural satellite [[243 Ida#Dactyl|Dactyl]] in images returned by the spacecraft, the first [[asteroid moon]] discovered.<ref>{{cite journal |last1=Belton |first1=Michael J.S. |last2=Chapman |first2=Clark R. |last3=Klaasen |first3=Kenneth P. |last4=Harch |first4=Ann P. |last5=Thomas |first5=Peter C. |last6=Veverka |first6=Joseph |last7=McEwen |first7=Alfred S. |last8=Pappalardo |first8=Robert T. |title = Galileo's Encounter with 243 Ida: An Overview of the Imaging Experiment |journal = Icarus |volume=120 |issue=1 |pages=2–3 |year=1996 |doi=10.1006/icar.1996.0032 |bibcode=1996Icar..120....1B |ref=CITEREFBelton et al1996|doi-access=free }}</ref>
* '''1994'''&nbsp;– [[Comet Shoemaker–Levy 9|Comet Shoemaker–Levy]] collides with Jupiter, providing the first direct observation of an extraterrestrial [[collision]] of Solar System objects.<ref>{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/comet.html |title=Comet Shoemaker–Levy 9 Collision with Jupiter |access-date=August 26, 2008 |publisher=[[National Space Science Data Center]] |date=February 2005 |archive-url=https://web.archive.org/web/20130219011148/http://nssdc.gsfc.nasa.gov/planetary/comet.html |archive-date=February 19, 2013 |url-status=dead }}</ref>
* '''1995'''&nbsp;– The ''Galileo'' becomes the first spacecraft to orbit Jupiter. Its atmospheric entry probe provides the first data taken within the planet itself.<ref name="GalileoProject" />
* '''1997'''&nbsp;– ''[[Mars Pathfinder]]'' deploys on Mars the first rover to operate outside the Earth–Moon system, the ''[[Sojourner (rover)|Sojourner]]'', which conducts many experiments on the Martian surface, both [[Sojourner (rover)#Control system|teleoperated and semi-autonomous]].<ref>{{cite book |url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf |title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 |page=195 |last1=Siddiqi |first1=Asif A. |lccn=2017059404 |isbn=978-1-62683-042-4| publisher=NASA History Program Office |edition=second |year=2018 |id=SP2018-4041 |series=The NASA history series |access-date=2019-11-04 |archive-date=2019-12-08 |archive-url=https://web.archive.org/web/20191208003521/https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf |url-status=live}}</ref>
* '''2000'''&nbsp;– ''[[NEAR Shoemaker]]'' probe provides the first detailed images of a [[near-Earth asteroid]], [[433 Eros|Eros]].<ref>{{cite news |url=https://solarsystem.nasa.gov/missions/near-shoemaker/in-depth/ |title=NEAR Shoemaker |publisher=NASA |access-date=April 26, 2021}}</ref>

==2001–present==
* '''2002'''&nbsp;– [[Chad Trujillo]] and [[Michael E. Brown|Michael Brown]] of [[Caltech]] at the [[Palomar Observatory]] discover the [[minor planet]] [[50000 Quaoar|Quaoar]] in the [[Kuiper belt]].<ref>{{cite web |title=50000 Quaoar (2002 LM60) |publisher=International Astronomical Union
|work=Minor Planet Center |url=https://www.minorplanetcenter.net/db_search/show_object?object_id=50000 |access-date=30 November 2017}}</ref>
* '''2003'''&nbsp;– M. Brown, C. Trujillo, and [[David L. Rabinowitz|David Rabinowitz]] discover [[90377 Sedna|Sedna]], a large [[trans-Neptunian object]] (TNO) with an unprecedented 12,000-year orbit.<ref>{{cite journal |title=Discovery of a Candidate Inner Oort Cloud Planetoid |author=Mike Brown |author2=David Rabinowitz |author3=Chad Trujillo |journal=Astrophysical Journal |bibcode=2004ApJ...617..645B |year=2004 |volume=617 |pages=645–649 |issue=1 |arxiv=astro-ph/0404456
|doi=10.1086/422095 }}</ref>
* '''2003'''&nbsp;– ''Voyager 1'' enters the [[termination shock]],  the point where the [[solar wind]] slows to subsonic speeds.<ref>{{cite news |url=http://edition.cnn.com/2003/TECH/space/11/05/voyager.solar.boundary/ |title=Spacecraft reaches edge of Solar System |first=Kate |last=Tobin |publisher=CNN 
|date=November 5, 2003 |access-date=August 19, 2013}}</ref>
* '''2004'''&nbsp;– ''Voyager 1'' sends back the first data ever obtained from within the Solar System's [[heliosheath]].<ref>{{cite web |url=http://solarsystem.nasa.gov/news/display.cfm?News_ID=36121 |title=Voyager 1 Sees Solar Wind Decline |publisher=NASA |date=December 13, 2010 |access-date=September 16, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20110614073203/http://solarsystem.nasa.gov/news/display.cfm?News_ID=36121 |archive-date=June 14, 2011}}</ref>
* '''2004'''&nbsp;– M. Brown, C. Trujillo, and D. Rabinowitz discover the TNO [[90482 Orcus|Orcus]].<ref>{{cite web |title=90482 Orcus (2004 DW) |work=Minor Planet Center |url=http://www.minorplanetcenter.net/db_search/show_object?object_id=90482 |access-date=3 April 2017}}</ref>
* '''2004'''&nbsp;– M. Brown, C. Trujillo, and D. Rabinowitz discover the Kuiper Belt Object (KBO) [[Haumea]].<ref>{{cite web |author= Michael E Brown |url=http://www.gps.caltech.edu/~mbrown/planetlila/ortiz/|title=The electronic trail of the discovery of 2003&nbsp;EL<sub>61</sub> |work=Caltech |access-date=2006-08-16 |url-status=live |archive-url=https://web.archive.org/web/20060901181611/http://www.gps.caltech.edu/~mbrown/planetlila/ortiz/ |archive-date=2006-09-01}}</ref> A second team led by [[José Luis Ortiz Moreno]] also [[Controversy over the discovery of Haumea|claims the discovery]].<ref>{{cite web |title=La historia de Ataecina vs Haumea |url=http://www.infoastro.com/200809/26ataecina-haumea.html |publisher=infoastro.com |author=Pablo Santos Sanz |date=2008-09-26 |access-date=2008-09-29 |language=es |url-status=live |archive-url=https://web.archive.org/web/20080929054518/http://www.infoastro.com/200809/26ataecina-haumea.html |archive-date=2008-09-29}}</ref>
* '''2004'''&nbsp;– The ''[[Cassini–Huygens]]'' spacecraft becomes the first to orbit Saturn. It discovers complex motions in the rings, several new small moons and [[cryovolcanism]] on the moon [[Enceladus (moon)|Enceladus]], studies the [[Saturn's hexagon]], and provides the first images from the surface of [[Titan (moon)|Titan]].<ref>{{cite web|title=Overview {{!}} Cassini|url=https://solarsystem.nasa.gov/missions/cassini/overview/|url-status=live|access-date=14 April 2021|website=[[NASA]]|archive-url=https://web.archive.org/web/20180926092908/https://solarsystem.nasa.gov/missions/cassini/overview/ |archive-date=September 26, 2018 }}</ref>
* '''2005'''&nbsp;– M. Brown, C. Trujillo, and D. Rabinowitz discover [[Eris (dwarf planet)|Eris]], a TNO more massive than Pluto,<ref>{{cite web |title=The discovery of 2003 UB313 Eris, the largest known dwarf planet |url = http://www.gps.caltech.edu/~mbrown/planetlila/ |last=Brown |first=Mike |publisher=California Institute of Technology, Department of Geological Sciences |date=2006 |access-date=May 3, 2007 |archive-url=https://web.archive.org/web/20110719163702/http://www.gps.caltech.edu/~mbrown/planetlila/ |archive-date=July 19, 2011 |url-status=live
}}</ref> and later, by other team led by Brown, also its moon, [[Dysnomia (moon)|Dysnomia]].<ref name="IAUC 8747">
{{cite journal |last=Green |first=D. W. E. |title=(134340) Pluto, (136199) Eris, and (136199) Eris I (Dysnomia) |date=13 September 2006
 |journal=[[IAU Circular]] |issue=8747 |page=1 |bibcode=2006IAUC.8747....1G |url=http://www.cbat.eps.harvard.edu/iauc/08700/08747.html
 |access-date=12 January 2012 }}</ref> Eris was first imaged in 2003, and is the most massive object discovered in the Solar System since Neptune's moon Triton in 1846.
* '''2005'''&nbsp;– M. Brown, C. Trujillo, and D. Rabinowitz discover another notable KBO, [[Makemake]].<ref>{{cite web |type=2019-05-12 last obs |title=JPL Small-Body Database Browser: 136472 Makemake ({{mp|2005 FY|9}}) |work=NASA Jet Propulsion Laboratory |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=136472 |access-date=2020-02-20}}</ref>
* '''2005'''&nbsp;– The ''[[Mars Exploration Rovers]]'' perform the first astronomical observations ever taken from the surface of another planet, imaging an eclipse by Mars's moon [[Phobos (moon)|Phobos]].<ref>{{cite web |url=https://www.theverge.com/2022/4/21/23035514/nasa-perseverance-rover-mars-eclipse-phobos |title=Check out NASA's latest footage of a solar eclipse on Mars |author=Mary Beth Griggs |date=April 21, 2022 |publisher=The Verge |access-date=April 19, 2022}}</ref>
[[File:PIA17356-MarsCuriosityRover-EclipseOfSunByPhobos.jpg|thumb|[[Annular eclipse]] of the Sun by Phobos as viewed by the Mars [[Curiosity (rover)|''Curiosity'' rover]] (20 August 2013).]]
* '''2005'''&nbsp;– ''[[Hayabusa]]'' spacecraft lands on asteroid [[25143 Itokawa|Itokawa]] and collect samples. It returned the samples to Earth in 2010.<ref>{{cite web |url=https://solarsystem.nasa.gov/missions/hayabusa/in-depth/ |title=Hayabusa |publisher=NASA's Solar System Exploration website |access-date=November 30, 2022}}</ref>
* '''2006'''&nbsp;– The 26th General Assembly of the [[IAU]] voted in favor of a [[IAU definition of planet|revised definition of a planet]]<ref>{{cite news |url=http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf |title=Definition of a Planet in the Solar System: Resolutions 5 and 6 |date=August 24, 2006 |work=IAU 2006 General Assembly |publisher=International Astronomical Union |access-date=January 26, 2008 |author=IAU}}</ref> and officially declared Ceres, Pluto, and Eris [[dwarf planet]]s.<ref>{{cite web |url=https://www.iau.org/news/pressreleases/detail/iau0603 |title=IAU 2006 General Assembly: Result of the IAU Resolution votes |date=24 August 2006}}</ref><ref>{{cite web |url=https://www.iau.org/news/pressreleases/detail/iau0605 |title=IAU names dwarf planet Eris |date=14 September 2006}}</ref>
* '''2007'''&nbsp;– Dwarf planet [[225088 Gonggong|Gonggong]], a large KBO, was discovered by [[Megan Schwamb]], M. Brown, and D. Rabinowitz.<ref>{{cite web |title=(225088) Gonggong = 2007 OR10 |work=[[Minor Planet Center]] |publisher=[[International Astronomical Union]] |url=https://www.minorplanetcenter.net/db_search/show_object?object_id=225088 |access-date=14 March 2021}}</ref>
* '''2008'''&nbsp;– The IAU declares Makemake and Haumea dwarf planets.<ref>{{cite web |url=https://www.iau.org/news/pressreleases/detail/iau0807 |title=IAU names fifth dwarf planet Haumea|website = IAU |date=19 July 2008}}</ref><ref>{{cite web |url=https://www.iau.org/news/pressreleases/detail/iau0806 |title=Fourth dwarf planet named Makemake |date=17 September 2008|website = IAU}}</ref>
* '''2011'''&nbsp;– ''[[Dawn (spacecraft)|Dawn]]'' spacecraft enters orbit around the large asteroid [[4 Vesta|Vesta]] making detailed measurements.<ref name="Dawn">{{cite news |url=http://www.space.com/17119-nasa-dawn-asteroid-spacecraft-vesta.html |title=NASA's Dawn Spacecraft Hits Snag on Trip to 2 Asteroids |work=Space.com |date=August 15, 2012 |access-date=August 27, 2012}}</ref>
* '''2012'''&nbsp;– Saturn's moon [[Methone (moon)|Methone]] is imaged up close by the ''[[Cassini–Huygens|Cassini]]'' spacecraft, revealing a remarkably smooth surface.<ref>{{cite web |url=http://saturn.jpl.nasa.gov/science/moons/methone/ |title=JPL (ca. 2008) ''Cassini Equinox Mission: Methone'' |access-date=2020-03-05 |archive-url=https://web.archive.org/web/20160412054200/http://saturn.jpl.nasa.gov/science/moons/methone/ |archive-date=2016-04-12 |url-status=dead }}</ref>
* '''2012'''&nbsp;– ''Dawn'' spacecraft breaks orbit of Vesta and heads for [[Ceres (dwarf planet)|Ceres]].<ref name="Dawn" />
* '''2013'''&nbsp;– ''[[MESSENGER]]'' spacecraft provides the first ever complete map of the surface of Mercury.<ref>{{cite web|url=http://messenger.jhuapl.edu/news_room/details.php?id=237 |title=MESSENGER Completes Its First Extended Mission at Mercury |publisher=JHU – APL |date=March 18, 2013 |access-date=July 8, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130729044412/http://messenger.jhuapl.edu/news_room/details.php?id=237 |archive-date=July 29, 2013}}</ref>
* '''2013'''&nbsp;– A team led by Felipe Braga Ribas discover a [[Rings of Chariklo|ring system]] around the minor planet and [[Centaur (small Solar System body)|centaur]] [[Chariklo]], the first of this kind ever detected.<ref>{{cite journal |last1=Braga-Ribas |first1=F. |last2=Sicardy |first2=B. |last3=Ortiz |first3=J. L. |last4=Snodgrass |first4=C. |last5=Roques |first5=F. |last6=Vieira-Martins |first6=R. |last7=Camargo |first7=J. I. B. |last8=Assafin |first8=M. |last9=Duffard |first9=R. |last10=Jehin |first10=E. |last11=Pollock |first11=J. |last12=Leiva |first12=R. |last13=Emilio |first13=M. |last14=Machado |first14=D. I. |last15=Colazo |first15=C. |last16=Lellouch |first16=E. |last17=Skottfelt |first17=J. |last18=Gillon |first18=M. |last19=Ligier |first19=N. |last20=Maquet |first20=L. |last21=Benedetti-Rossi |first21=G. |last22=Gomes |first22=A. Ramos |last23=Kervella |first23=P. |last24=Monteiro |first24=H. |last25=Sfair |first25=R. |last26=Moutamid |first26=M. El |last27=Tancredi |first27=G. |last28=Spagnotto |first28=J. |last29=Maury |first29=A. |last30=Morales |first30=N. |last31=Gil-Hutton |first31=R. |last32=Roland |first32=S. |last33=Ceretta |first33=A. |last34=Gu |first34=S.-h. |last35=Wang |first35=X.-b. |last36=Harpsøe |first36=K. |last37=Rabus |first37=M. |last38=Manfroid |first38=J. |last39=Opitom |first39=C. |last40=Vanzi |first40=L. |last41=Mehret |first41=L. |last42=Lorenzini |first42=L. |last43=Schneiter |first43=E. M. |last44=Melia |first44=R. |last45=Lecacheux |first45=J. |last46=Colas |first46=F. |last47=Vachier |first47=F. |last48=Widemann |first48=T. |last49=Almenares |first49=L. |last50=Sandness |first50=R. G. |last51=Char |first51=F. |last52=Perez |first52=V. |last53=Lemos |first53=P. |last54=Martinez |first54=N. |last55=Jørgensen |first55=U. G. |last56=Dominik |first56=M. |last57=Roig |first57=F. |last58=Reichart |first58=D. E. |last59=LaCluyze |first59=A. P. |last60=Haislip |first60=J. B. |last61=Ivarsen |first61=K. M. |last62=Moore |first62=J. P. |last63=Frank |first63=N. R. |last64=Lambas |first64=D. G. |title=A ring system detected around the Centaur (10199) Chariklo |journal=Nature |date=April 2014 |volume=508 |issue=7494 |pages=72–75 |doi=10.1038/nature13155 |pmid=24670644 |arxiv=1409.7259 |bibcode=2014Natur.508...72B }}</ref>
* '''2014'''&nbsp;– ''[[Rosetta (spacecraft)|Rosetta]]'' spacecraft becomes the first [[comet]] orbiter (around [[67P/Churyumov–Gerasimenko]]),<ref>{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions |title=Rosetta's Frequently Asked Questions |publisher=European Space Agency |access-date=24 May 2014}}</ref> and deploys on it the first comet lander ''[[Philae (spacecraft)|Philae]]'' that collected close-up data from the comet's surface.<ref>{{cite news |url=http://www.skyandtelescope.com/astronomy-news/philae-lands-three-times-111220143/ |title=Philae Lands on Its Comet – Three Times! |work=[[Sky & Telescope]] |first=Kelly |last=Beatty |date=12 November 2014 |access-date=26 November 2014}}</ref>
* '''2015'''&nbsp;– ''Dawn'' spacecraft enters orbit around the dwarf planet Ceres making detailed measurements.<ref>{{cite web |last1=Landau |first1=Elizabeth |last2=Brown |first2=Dwayne |title=NASA Spacecraft Becomes First to Orbit a Dwarf Planet |url=http://www.jpl.nasa.gov/news/news.php?feature=4503 |date=March 6, 2015 |publisher=NASA |access-date=March 6, 2015}}</ref>
* '''2015'''&nbsp;– ''[[New Horizons]]'' spacecraft flies by Pluto, providing the first ever sharp images of its surface, and its largest moon Charon.<ref>{{cite web |title=NASA's Three-Billion-Mile Journey to Pluto Reaches Historic Encounter |url=http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20150714-2 |publisher=[[Johns Hopkins University Applied Physics Laboratory]] |date=July 14, 2015}}</ref>
* '''2017'''&nbsp;– [['Oumuamua]], the first known [[interstellar object]] crossing the Solar System, is identified.<ref>{{cite press release |website=Gemini Observatory |url=http://www.gemini.edu/node/12729 |title=First Known Interstellar Visitor is an 'Oddball' |date=20 November 2017 |access-date=28 November 2017 |archive-date=23 November 2017 |archive-url=https://web.archive.org/web/20171123071154/http://www.gemini.edu/node/12729 |url-status=live }}</ref>
* '''2019'''&nbsp;– Closest approach of ''New Horizons'' to [[486958 Arrokoth#Exploration|Arrokoth]], a KBO farther than Pluto.<ref>{{cite conference |title=New Horizons Kuiper Belt Extended Mission |url=http://pluto.jhuapl.edu/News-Center/Press-Conferences/2017-12-12/resources/2017_NH_AGU_PA.pdf |first1=Jim |last1=Green |first2=S. Alan |last2=Stern |date=12 December 2017 |conference=2017 AGU Fall Meeting |publisher=Applied Physics Laboratory |pages=12–15 |access-date=26 December 2018 |archive-url=https://web.archive.org/web/20181226234838/http://pluto.jhuapl.edu/News-Center/Press-Conferences/2017-12-12/resources/2017_NH_AGU_PA.pdf
|archive-date=26 December 2018 |url-status=dead |df= dmy-all}}</ref>
* '''2019'''&nbsp;– [[2I/Borisov]], the first interstellar comet and second interstellar object, is discovered.<ref>{{cite press release
|title=Interstellar comet with a familiar look |publisher=Astronomical Observatory, [[Jagiellonian University]] |date=14 October 2019
|website=[[EurekAlert!]] |url=https://www.eurekalert.org/pub_releases/2019-10/aoju-icw101119.php |access-date=14 October 2014}}</ref>
* '''2022'''&nbsp;– The ''[[Double Asteroid Redirection Test]]'' (DART) spacecraft mission intentionally crashed into [[Dimorphos]], the [[minor-planet moon]] of the asteroid [[65803 Didymos|Didymos]], deviating (slightly) the orbit of a Solar System body for the first time ever.<ref>{{cite web |date=27 September 2022 |title=NASA's DART Mission Hits Asteroid in First-Ever Planetary Defense Test |url=https://www.nasa.gov/press-release/nasa-s-dart-mission-hits-asteroid-in-first-ever-planetary-defense-test |publisher=NASA}}</ref> While DART hosted no scientific payload, its camera took closeup photos of the two objects, and a secondary spacecraft, the [[LICIACube]], also gathered related scientific data.<ref>{{cite news|url=https://gizmodo.com/liciacube-images-dart-asteroid-impact-1849585958 |title=First Asteroid Impact Images from DART's Companion Show Tentacle-Like Debris Plume|author=George Dvorsky|date=September 27, 2022|publisher=Gizmodo}}</ref>

==See also==
* [[Discovery and exploration of the Solar System]]
* [[Timeline of discovery of Solar System planets and their moons]]
* [[Timeline of Solar System exploration]]
* [[Timeline of first images of Earth from space]]
* [[List of former planets]]
* [[List of hypothetical Solar System objects]] in astronomy
* [[Historical models of the Solar System]]
* [[History of astronomy]]
* [[Timeline of cosmological theories]]

The number of currently known, or observed, objects of the Solar System are in the hundreds of thousands. Many of them are listed in the following articles:

* [[List of Solar System objects]]
* [[List of gravitationally rounded objects of the Solar System]]
* [[List of natural satellites]]
* [[List of possible dwarf planets]]
* [[List of minor planets]] (numbered) and [[List of unnumbered minor planets]]
* [[List of trans-Neptunian objects]] (numbered) and [[List of unnumbered trans-Neptunian objects]]
* [[Lists of comets]]

==References==
{{Reflist}}

{{Solar System|state=expanded}}
{{Solar System models}}

[[Category:History of astronomy]]
[[Category:Astronomy timelines|Solar System]]
[[Category:Discovery and exploration of the Solar System]]
[[Category:Solar System]]