Humans (Homo sapiens) have inhabited the Earth in the last 300,000 years at least,[1] and they had witnessed directly observable astronomical and geological phenomena. For millennia, these have arose admiration and curiosity, being admitted as of superhuman nature and scale. Multiple imaginative interpretations were being fixed in oral traditions of difficult dating, and incorporated into a variety of belief systems, as animism, shamanism, mythology, religion and/or philosophy.
Although such phenomena are not "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.
Nightly apparent movement of the celestial sphere with its main features regarded as "fixed": stars, the brightest of them forming casual groupings known as constellations, under different names and shapes in many cultures. Different constellations are viewed in different seasons and latitudes. 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. Tides. Recognition of meteorological phenomena as sub-lunar.
Yearly 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 calendars.
2nd millennium BCE – Earliest possible date for the composition of the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy[2] of a list of observations of the motions of the planet Venus, and the oldest planetary table currently known.
2nd millennium BCE – Babylonian astronomers identify the inner planets 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.[3]
Late 2nd millennium BCE – 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.Script error: No such module "Unsubst".
Template:Circa560 BCE – Anaximander posits a mechanical model of the world: a cylindrical Earth[11] 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.[12] But he starts to feed the idea of celestial mechanics as different of the notion of planets being heavenly deities, leaving mythology aside.
Template:Circa475 BCE – 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, the morning-star (Venus), and by some, the first to claim that moonlight is a reflection of sunlight.[13]
Template:Circa450 BCE – 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 rocky, thus opaque, and closer to the Earth than the Sun.[14]
Template:Circa400 BCE – Philolaus and other Pythagoreans propose 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.[15] Due to philosophical concerns 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.[16]
Template:Circa360 BCE – Plato claims in his Timaeus that 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.[17]
Template:Circa330 BCE – Heraclides Ponticus is said to be the first Greek who proposes that the Earth rotates on its axis, from west to east, once every 24 hours, contradicting Aristotle's teachings. Simplicius says that Heraclides proposed that the irregular movements of the planets can be explained if the Earth moves while the Sun stays still,[22] but these statements are disputed.[23]
Template:Circa150 BCE – According to Strabo (1.1.9), Seleucus of Seleucia is the first to state that the tides 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.[29]
Template:Circa87 BCE – 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.[32]
28 BCE – Chinese history book Book of Han makes earliest known dated record of sunspot.[33]
Template:Circa150 CE – 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, stars (including some objects as nebulae, supernovas 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 constellations, comets and other astronomical phenomena.[34] 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.
Template:Circa420 – 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.[35]
Middle Ages
Template:Circa500 – Indian mathematician-astronomer Aryabhata accurately computes the solar and lunar eclipses, and the length of Earth's revolution around the Sun.
Template:Circa500 – 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.
Template:Circa500 – Aryabhata discovers the rotation of the Earth by conducting experiments and giving empirical examples for his theories. He also explains the cause of day and night through the 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.[36][37][38]
Template:Circa620 – Indian mathematician-astronomer Brahmagupta describe gravity as a attractive force by the term guruvatkarshan.[39]
628 – Brahmagupta gives methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and calculations of the solar and lunar eclipses.[40]
850 – Al-Farghani (Alfraganus) translated and wrote commentary on Ptolemy'sAlmagest and gave values for the motion of the ecliptic, and the precessional movement of the heavenly bodies based on the values given by Ptolemy and Hipparchus.[43]
1019 – Al-Biruni observes and describes the lunar eclipse on September 17 in detail and gives the exact latitudes of the stars during it.[44]File:Lunar phases al-Biruni.jpgAn 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
Template:Circa1030 – 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.[45]
Template:Circa1060 – 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.[46] He was the first to demonstrate the motion of the 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.[47] Al-Zarqālī also contributed to the famous Tables of Toledo.
Template:Circa1200 – Fakhr al-Din al-Razi, in dealing with his conception of physics and the physical world, rejected the Aristotelian and 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."[49]
Template:Circa1300 – Jewish astronomer 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.[52][53]
Template:Circa1350 – 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 and solar orbits, measuring the angles and distance between ecliptics and calculating stellar and 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 axis.[56][57]
1440 – Nicholas of Cusa proposes that the Earth rotates on its axis in his book, On Learned Ignorance.[58] Like Oresme, he also wrote about the possibility of the plurality of worlds.[59]
16th century
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1501 – Indian astronomer Nilakantha Somayaji proposes a universe in which the planets orbit the Sun, but the Sun orbits the Earth.[60]
1577 – Tycho Brahe records the position of the Great Comet of that year as viewed from Uraniborg (in the island Hven, near Copenhagen) and compares it with that observed by 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.[67]
1582 – Pope Gregory XIII introduces the Gregorian calendar, an enhanced solar calendar more accurate than the previous Roman Julian calendar.[68] The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day '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 – 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 substanceTemplate:Snda "pure air", aether, or spiritusTemplate:Sndthat offered no resistance to the heavenly bodies which, in Bruno's view, rather than being fixed, moved under their own 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,[69] 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".[70]
1588 – 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.[71]
1604 – Galileo Galilei correctly hypothesized that the distance of a falling object is proportional to the square of the time elapsed.[73]
1609 – Johannes Kepler states his first two empirical 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.[74]
1609 – 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"),[76] Galileo was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and craters. 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".
1648 – 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.[87]
1659 – Huygens estimated a value of about 24,000 Earth radii for the 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.[90]
1665 – Cassini determines the rotational speeds of Jupiter, Mars, and Venus.[91]
1729 – 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.[102]
1758 – Johann Palitzsch observes the return of the comet that Edmond Halley had anticipated in 1705.[110] The gravitational attraction of Jupiter had slowed the return by 618 days. Parisian astronomer La Caille suggests it should be named "Halley's Comet".[111]
1775 – Charles Hutton, based on his analysis of the Schiehallion experiment, shows the Earth has a density of at least 4,500 kg·m−3 and suggests that it has a planetary core made of metal. (In comparison with the modern accepted figure of 5,515 kg·m−3, the density of the Earth had been computed with an error of less than 20%.)[115]
1801 – Giuseppe Piazzi discovers 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.[122]
1802 – Heinrich Wilhelm Olbers discovers Pallas, at roughly the same distance to the Sun than Ceres.[123] He proposed that the two objects were the remnants of a destroyed planet,[124] and predicted that more of these pieces would be found.
1802 – Due their star-like apparience, William Herschel suggested Ceres and Pallas, and similar objects if found, be placed into a separate category, named asteroids, although they were still counted among the planets for some decades.[125]
1845 – John Adams predicts the existence and location of an eighth planet from irregularities in the orbit of Uranus.[133]
1845 – Karl Ludwig Hencke discovers a fifth body between Mars and Jupiter, Astraea[134] 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.[135] Since then, the region they occupy between Mars and Jupiter is known as the asteroid belt.
1846 – Urbain Le Verrier predicts the existence and location of an eighth planet from irregularities in the orbit of Uranus.[133]
1849 – Édouard Roche finds the limiting radius of 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.[139]
1849 – Annibale de Gasparis discovers the asteroid Hygiea, the fourth largest asteroid in the Solar System by both volume and mass.[140]
1856 – 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.[142]
1862 – 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.[144]
1866 – Giovanni Schiaparelli realizes that meteor streams occur when the Earth passes through the orbit of a comet that has left debris along its path.[145]
1868 – 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.[146]
1895 – 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 intelligent life forms.[150]
1897 – William Thomson, 1st Baron Kelvin, based on the thermal radiation rate and the 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.[151]
1904 – 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.[153]
1920 – In the Great Debate between Harlow Shapley and Heber Curtis, galaxies are finally recognized as objects beyond the Milky Way, and the Milky Way as a galaxy proper.[161] Within it lies the Solar System.
1935 – The Explorer II balloon reached a record altitude of 22,066 m (72,395 ft), enabling its occupants to photograph the curvature of the Earth for the first time.[166]
1946 – American launch of a camera-equipped V-2 rocket provides the first image of the Earth from space.[170]
1949 – Gerard Kuiper discovers Uranus's moon Miranda and Neptune's moon Nereid.[169]
1950 – Jan Oort suggests the presence of a cometary reservoir in the outer limits of the Solar System, the Oort cloud.[171]
1951 – Gerard Kuiper argues for an annular reservoir of comets between 40 and 100 astronomical units from the Sun having formed early in the Solar System's evolution, but he did not think that such a belt still existed today.[172] Decades later, this region was named after him, the Kuiper belt.
1958–1976
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1959 – Explorer 6 sends the first image of the entire Earth from space.[174]
1959 – Luna 3 sends the first images of another celestial body, the Moon, from space, including its unseen far side.[175]
1962 – Mariner 2 Venus flyby performs the first closeup observations of another planet.[176]
1964 – Mariner 4 spacecraft provides the first detailed images of the surface of Mars.[177]
1966 – Luna 9 Moon lander provides the first images from the surface of another celestial body.[178]
1967 – Venera 4 provides the first information on Venus's dense atmosphere.[179]
1968 – Apollo 8 becomes the first crewed lunar mission, providing historic images of the whole Earth.[180]
1969 – Apollo 11 mission landed on the Moon, first humans walking upon it.[181] They return the first lunar samples back to Earth.[182]
1970 – Venera 7 Venus lander sends back the first information successfully obtained from the surface of another planet.[183]
1971 – Mariner 9 Mars spacecraft becomes the first to successfully orbit another planet.[184] It provides the first detailed maps of the Martian surface,[185] 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 – Mars 3 lands on Mars, and transmits the first partial image from the surface of another planet.[186]
1978 – 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.[195]
1979 – Pioneer 11 flies by Saturn, providing the first ever closeup images of the planet and its rings. It discovers the planet's F ring and determines that its moon Titan has a thick atmosphere.[196]
1979 – Goldreich and Tremaine postulate that Saturn's F ring is maintained by shepherd moons, a prediction that would be confirmed by observations.[197]
1979 – Voyager 2 flies by Jupiter and discovers evidence of an ocean under the surface of its moon Europa.[199]
1980 – Voyager 1 flies by Saturn and takes the first images of Titan.[200] However, its atmosphere is opaque to visible light, so its surface remains obscured.
1982 – 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.[201]
1986 – Voyager 2 provides the first ever detailed images of Uranus, its moons and rings.[199]
1986 – The 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.[202]
1988 – Martin Duncan, Thomas Quinn, and Scott Tremaine demonstrate that short-period comets come primarily from the Kuiper Belt and not the Oort cloud.[203]
1989 – Voyager 2 provides the first ever detailed images of Neptune, its moons and rings.[199]
1993 – Asteroid Ida is visited by the Galileo before heading to Jupiter. Mission member Ann Harch discovers its natural satellite Dactyl in images returned by the spacecraft, the first asteroid moon discovered.[214]
1994 – Comet Shoemaker–Levy collides with Jupiter, providing the first direct observation of an extraterrestrial collision of Solar System objects.[215]
1995 – The Galileo becomes the first spacecraft to orbit Jupiter. Its atmospheric entry probe provides the first data taken within the planet itself.[212]
2004 – 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, studies the Saturn's hexagon, and provides the first images from the surface of Titan.[225]
2005 – M. Brown, C. Trujillo, and D. Rabinowitz discover Eris, a TNO more massive than Pluto,[226] and later, by other team led by Brown, also its moon, Dysnomia.[227] 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 – M. Brown, C. Trujillo, and D. Rabinowitz discover another notable KBO, Makemake.[228]
2005 – 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.[229]
2019 – Closest approach of New Horizons to Arrokoth, a KBO farther than Pluto.[246]
2019 – 2I/Borisov, the first interstellar comet and second interstellar object, is discovered.[247]
2022 – The Double Asteroid Redirection Test (DART) spacecraft mission intentionally crashed into Dimorphos, the minor-planet moon of the asteroid Didymos, deviating (slightly) the orbit of a Solar System body for the first time ever.[248] 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.[249]
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:
↑"A column of stone", Aetius reports in De Fide (III, 7, 1), or "similar to a pillar-shaped stone", pseudo-Plutarch (III, 10).
↑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".
↑"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.
↑Owen Gingerich, Gutenberg's Gift pp. 319–28 in Library and information services in astronomy V (Astron. Soc. Pacific Conference Series vol. 377, 2007).
↑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.
↑Script error: No such module "Citation/CS1". 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.
↑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.
↑ abcNational Aeronautics and Space Administration "Voyager 2" NASA Science: Solar System Exploration. Updated January 26, 2018. Accessed December 12, 2018.
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