View source for Halley's Comet

{{Short description|Periodic comet}}
{{Other uses|Halley's Comet (disambiguation)}}
{{Distinguish|text=the asteroid of the same name, [[2688 Halley]]}}
{{Featured article}}
{{Use dmy dates|date=September 2018}}{{Use British English|date=July 2024}}
{{Infobox comet
| name            = 1P/Halley
| image           = Lspn comet halley.jpg
| caption         = Halley's Comet photographed by [[William Liller]] from [[Easter Island]] on 8 March 1986
| discoverer      = [[Edmond Halley]]{{efn|The comet is known since at least the ancient times}}<br>{{small|(recognition of [[periodic comet|periodicity]])}}
| discovery_date  = 25 December 1758<br>{{small|(first predicted return)}}
| designations    = Various ''(See [[Halley's Comet#List of apparitions|Apparitions]])''
| orbit_ref       = {{r|jpldata|MPC}}
| epoch           = 4 August 2061 ([[Julian day|JD]] 2474040.5)
| observation_arc = 2,243 years
| earliest_precovery_date = May 240 BC
| obs             = 8,518
| perihelion      = 0.59278 AU{{r|Horizons2061}}
| aphelion        = 35.14 AU{{r|Horizons2023}}
| semimajor       = 17.737 AU
| eccentricity    = 0.96658
| period          = 74.7 years
| inclination     = 161.96°
| asc_node        = 59.396°
| arg_peri        = 112.05°
| mean            = 0.07323°
| tjup            = –0.598
| Earth_moid      = 0.075 AU
| Jupiter_moid    = 0.783 AU
| physical_ref    = 
| dimensions      ={{val|14.42|x|7.4|x|7.4|ul=km}} (''[[Giotto (spacecraft)|Giotto]]''){{r|Lamy2004}}<br/>{{val|15.3|x|7.21|x|7.21|u=km}} (''[[Vega program|Vega]]''){{r|Lamy2004}}
| escape_velocity = ~0.002 km/s
| mean_diameter   = {{cvt|11|km|mi}}{{r|Lamy2004}}
| rotation        = 2.2 days (52.8 hours){{r|Peale1989}}
| density         = {{unbulleted|{{val|0.55|0.25|u=g/cm3}}{{r|situ}}|{{val|0.2|-|1.5|u=g/cm3}} (est.){{r|Peale1989November}}}}
| albedo          = 0.04{{r|dark}}
| mass            = {{val|2.2|0.9|e=14|ul=kg}}{{r|mass}}
| M1              = 5.5
| M2              = 13.6
| magnitude       = 2.1<br>{{small|(1986 apparition)}}{{r|sten}}
| last_p          = 8 February 1986
| next_p          = {{unbulleted|28 July 2061{{r|Horizons2061|Kinoshita}}|≈27 March 2134{{r|Kinoshita|Horizons2134}}}}
}}

'''Halley's Comet'''{{Efn|See [[#Pronunciation|Pronunciation]]}} is the only known [[List of periodic comets|short-period]] [[comet]] that is consistently visible to the [[naked eye]] from [[Earth]],<ref name="Delehanty"/> appearing every 72–80 years,<ref name="Brady1987"/> though with the majority of recorded apparitions (25 of 30) occurring after 75–77 years. It last appeared in the inner parts of the [[Solar System]] in 1986 and will next appear in mid-2061. Officially designated '''1P/Halley''', it is also commonly called '''Comet Halley''', or sometimes simply '''Halley'''. 

Halley's periodic returns to the [[Solar System#Inner Solar System|inner Solar System]] have been observed and recorded by astronomers around the world since at least 240 BC, but it was not until 1705 that the English astronomer [[Edmond Halley]] understood that these appearances were re-appearances of the same comet. As a result of this discovery, the comet is named after Halley.

In March 1986, during its latest visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by a [[spacecraft]], ESA's ''[[Giotto (spacecraft)|Giotto]]'' mission, providing the first observational data on the structure of a [[comet nucleus]] and the mechanism of [[coma (cometary)|coma]] and [[comet tail|tail]] formation. These observations supported several longstanding hypotheses about comet construction, particularly [[Fred Whipple]]'s [[Comet nucleus#"Dirty snowball"|"dirty snowball"]] model, which correctly predicted that Halley would be composed of a mixture of [[Volatile (astrogeology)|volatile ices]]—such as [[water]], [[carbon dioxide]], [[ammonia]]—and [[cosmic dust|dust]]. The missions also provided data that substantially reformed and reconfigured these ideas; for instance, it is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy. It was also visited by the two spacecrafts of the [[Vega program]], Vega 1 & 2, on March 6 and March 9, respectively. They went as close as 8,890 km (5,520 mi), and 8,030 km (4,990 mi), providing data on Halley's dimensions, shape, temperature, and surface properties.

{{TOC limit|limit=3}}

==Pronunciation==
Comet Halley is usually pronounced {{IPAc-en|ˈ|h|æ|l|i}}, rhyming with ''valley'', or sometimes {{IPAc-en|ˈ|h|eɪ|l|i}}, rhyming with ''daily''.<ref name="Webster"/><ref name="Ridpath2015"/> As to the surname Halley, [[Colin Ronan]], one of Edmond Halley's biographers, preferred {{IPAc-en|ˈ|h|ɔː|l|i}}, rhyming with ''crawly''.<ref>That is, with the vowel of ''hall'' and in some accents homophonous with ''holly''.</ref> Spellings of Halley's name during his lifetime included ''Hailey'', ''Haley'', ''Hayley'', ''Halley'', ''Haly'', ''Hawley'', and ''Hawly'', so its contemporary pronunciation is uncertain, but the version rhyming with ''valley'' seems to be preferred by modern bearers of the surname.<ref name="NYT_Q&A"/>

==Computation of orbit==
Halley was the first comet to be recognised as periodic. Until the [[Renaissance]], the philosophical consensus on the nature of comets, promoted by [[Aristotle]], was that they were disturbances in Earth's atmosphere. This idea was disproven in 1577 by [[Tycho Brahe]], who used [[parallax]] measurements to show that comets must lie beyond the [[Moon]]. Many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System.{{sfn|Lancaster-Brown|1985|pp=14, 25}} In 1687, [[Isaac Newton|Sir Isaac Newton]] published his ''[[Philosophiæ Naturalis Principia Mathematica]]'', in which he outlined his laws of [[gravity]] and motion. His work on comets was decidedly incomplete. Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun (he was later found to be correct; see [[Great Comet of 1680|Newton's Comet]]),{{sfn|Lancaster-Brown|1985|p=35}} he was initially unable to completely reconcile comets into his model.<ref name="Hughes1988"/>

[[File:Excerpt of Halley's Letter to Newton About Comets' Orbits (MS Add.3982).jpg|thumb|upright=1.75|"I must entreat you to procure for me of Mr [[John Flamsteed|Flamsteed]] what he has observed of the Comett of 1682 particularly in the month of September, for I am more and more confirmed that we have seen that Comett now three times, since [[:wikt:yͤ|yͤ]] Yeare 1531, he will not deny it you, though I know he will me." —Excerpt of [[Edmond Halley|Halley]]'s letter to [[Isaac Newton|Newton]] about comet's orbits (28 September 1695)]]
Ultimately, it was Newton's friend, editor and publisher, [[Edmond Halley]], who, in his 1705 ''Synopsis of the Astronomy of Comets'', used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits.{{sfn|Lancaster-Brown|1985|p=76}} Having compiled a list of 24 comet observations, he calculated that the [[orbital elements]] of a second comet that had appeared in 1682 were nearly the same as those of two comets that had appeared in 1531 (observed by [[Petrus Apianus]]) and 1607 (observed by [[Johannes Kepler]]).{{sfn|Lancaster-Brown|1985|p=76}} Halley thus concluded that all three comets were the same object returning about every 76 years, a period that has since been found to vary between 72 and 80 years.<ref name="Brady1987"/> After a rough estimate of the [[Perturbation (astronomy)|perturbations]] the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758.{{sfn|Lancaster-Brown|1985|p=78}} He personally observed the comet around [[perihelion]] in September 1682,<ref name="yeo_p81"/> but died in 1742 before he could observe its predicted return.{{sfn|Lancaster-Brown|1985|p=88}}
[[File:Francis williams.jpg|thumb|Jamaican polymath [[Francis Williams (poet)|Francis Williams]] (portrait attributed to [[William Williams (artist)|William Williams]], {{circa|1760}}). The only contemporary illustration of an astronomer detecting the comet's return.]]
Halley's prediction of the comet's return proved to be correct, although it was not seen until 25 December 1758, by [[Johann Georg Palitzsch]], a German farmer and amateur astronomer. Other observers from throughout Europe and its colonies sent confirmations to Paris after the comet brightened early the following year. In the Americas, [[John Winthrop (educator)|John Winthrop]] lectured at [[Harvard University]] to explain the implications of the comet's reappearance for Newtonian mechanics and [[natural theology]].<ref name="Greene1954"/>

Another independent recognition that the comet had returned was made by the Jamaican astronomer [[Francis Williams (poet)|Francis Williams]], but his observations did not reach Europe.<ref name="VAM"/><ref name="Dabhoiwala2024"/> A unique portrait commissioned by Williams demonstrates the impact of the comet's return on period astronomers. Williams' hand rests on page 521 of the third edition of Newton's ''[[Philosophiæ Naturalis Principia Mathematica|Principia]]'' with procedures to predict comet sightings. The white smudge in the sky is probably a depiction of Halley's comet relative to the [[constellations]] in March 1759, and the chord hanging above the book likely represents the comet's orbit.<ref name="Guardian_17Oct2024"/><ref name="Dabhoiwala2024"/> In 2024, using [[Cultural property radiography|X-ray imaging]], the painting was shown to depict the field of stars in which the comet would have been visible in 1759. Williams likely commissioned the portrait to commemorate his observations.<ref name="Dabhoiwala2024"/>

The comet did not pass through its [[Apsis|perihelion]] until 13 March 1759, the attraction of [[Jupiter]] and [[Saturn]] having caused a delay of 618 days.{{sfn|Lancaster-Brown|1985|p=86}} This effect was computed before its return (with a one-month error to 13 April){{sfn|Sagan|Druyan|1985|p=74}} by a team of three French mathematicians, [[Alexis Clairaut]], [[Jérôme Lalande|Joseph Lalande]], and [[Nicole-Reine Lepaute]].{{sfn|Lancaster-Brown|1985|pp=84–85}} The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun.<ref name="hughes1987"/> It was also one of the earliest successful tests of [[Newtonian physics]], and a clear demonstration of its explanatory power.<ref name="hughes1987"/> The comet was first named in Halley's honour by French astronomer [[Nicolas-Louis de Lacaille]] in 1759.<ref name="hughes1987"/>

Some scholars have proposed that first-century [[Mesopotamia]]n astronomers already had recognised Halley's Comet as periodic.<ref name="Brodetsky"/> This theory notes a passage in the Babylonian [[Talmud]], tractate [[Horayot#Aggada|Horayot]]<ref name="Horioth"/> that refers to "a star which appears once in seventy years that makes the captains of the ships err".{{sfn|Rayner|1998|pp=108–111}} It has also been suggested that the passage may have referred to the variable star [[Mira]], whose brightness oscillates with a period of sixty years.<ref name="Veron1982"/>

Researchers in 1981 attempting to calculate the past orbits of Halley by [[numerical integration]] starting from accurate observations in the seventeenth and eighteenth centuries could not produce accurate results further back than 837 owing to a close approach to Earth in that year. It was necessary to use [[Historical comet observations in China|ancient Chinese comet observations]] to constrain their calculations.<ref>{{cite journal |author-link1=F. Richard Stephenson |last1=Stephenson |first1=F. Richard |last2=Yau |first2=Kevin K. C. |title=Oriental tales of Halley's Comet |journal=New Scientist |volume=103 |issue=1423 |pages=30–32 |date=27 September 1984 |issn=0262-4079}}</ref>

==Orbit and origin==
{{multiple image
|align=right
|direction=vertical
|width=200
|image_gap=10
|image1=Halley's Comet animation.gif
|caption1=The orbital path of Halley, against the orbits of the planets (''animation'')
|image2=Orionid12n.jpg
|caption2=[[Orionids|Orionid meteor]] originating from Halley's Comet streaking the sky below the [[Milky Way]] and to the right of [[Venus]]
}}
Halley's orbital period has varied between 74 and 80 years since 240 BC.<ref name="yeo"/> Its orbit around the [[Sun]] is highly [[Ellipse|elliptical]], with an [[orbital eccentricity]] of 0.967 (with 0 being a circle and 1 being a [[parabolic trajectory]]). The perihelion, the point in the comet's orbit when it is nearest the Sun, is {{convert|0.59|au|e6km|abbr=unit|lk=on}}. This is between the orbits of [[Mercury (planet)|Mercury]] and [[Venus]]. Its [[aphelion]], or farthest distance from the Sun, is {{convert|35|au|e9km|abbr=unit}}, roughly the orbital distance of [[Pluto]]. Unlike the overwhelming majority of objects in the Solar System, Halley's orbit is [[Retrograde and direct motion|retrograde]]; it orbits the Sun in the opposite direction to the planets, or, clockwise from above the Sun's north pole.<ref name="Hromakina2021"/> The orbit is inclined by 18° to the [[ecliptic]], with much of it lying south of the ecliptic.<ref name="Russell1988"/> This is usually represented as 162°, to account for Halley's retrograde orbit.<ref name="NASA_chapter5"/><ref name=MPC/> The 1910 passage was at a [[relative velocity]] of {{convert|70.56|km/s|mph|abbr=on}}.<ref name="jpldata"/> Because its orbit comes close to Earth's in two places, Halley is associated with two [[meteor shower]]s: the [[Eta Aquariids]] in early May, and the [[Orionids]] in late October.<ref name="Streams"/>

Halley is classified as a ''periodic'' or ''short-period [[comet]]'': one with an orbit lasting 200 years or less.<ref name="Morbidelli2006"/> This contrasts it with long-period comets, whose orbits last for thousands of years. Periodic comets have an average inclination to the ecliptic of only ten degrees, and an orbital period of just 6.5 years, so Halley's orbit is atypical.<ref name="hughes1987"/> Most short-period comets (those with orbital periods shorter than 20 years and inclinations of 30 degrees or less) are called Jupiter-family comets.<ref name="Morbidelli2006"/> Those resembling Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets.<ref name="Morbidelli2006"/><ref name="jewitt2002"/> {{As of|2024}}, 105 Halley-type comets have been observed, compared with 816 identified Jupiter-family comets.<ref name="jpl_JFC-list"/><ref name="yfernandez"/>

The orbits of the Halley-type comets suggest that they were originally long-period comets whose orbits were perturbed by the gravity of the giant planets and directed into the inner Solar System.<ref name="Morbidelli2006"/> If Halley was once a long-period comet, it is likely to have originated in the [[Oort cloud]],<ref name="jewitt2002"/> a sphere of cometary bodies around [[Oort Cloud#Structure and composition|20,000–50,000 au]] from the Sun. Conversely the Jupiter-family comets are generally believed to originate in the [[Kuiper belt]],<ref name="jewitt2002"/> a flat disc of icy debris between 30 au (Neptune's orbit) and 50 au from the Sun (in the [[scattered disc]]). Another point of origin for the Halley-type comets was proposed in 2008, when a [[trans-Neptunian object]] with a retrograde orbit similar to Halley's was discovered, {{mpl|2008 KV|42}}, whose orbit takes it from just outside that of Uranus to twice the distance of Pluto. It may be a member of a new population of small Solar System bodies that serves as the source of Halley-type comets.<ref name="Gladman2009"/>

Halley has probably been in its current orbit for 16,000–200,000 years, although it is not possible to numerically integrate its orbit for more than a few tens of apparitions, and close approaches before 837 AD can only be verified from recorded observations.<ref name="Olsson1987"/> The non-gravitational effects can be crucial;<ref name="Olsson1987"/> as Halley approaches the Sun, it expels jets of sublimating gas from its surface, which knock it very slightly off its orbital path. These orbital changes cause delays in its [[perihelion]] passage of four days on average.{{sfn|Yeomans|1991|pp=260–261}}

In 1989, [[Boris Chirikov]] and Vitold Vecheslavov performed an analysis of 46 apparitions of Halley's Comet taken from historical records and computer simulations, which showed that its dynamics were chaotic and unpredictable on long timescales.<ref name="Chirikov1989b"/> Halley's projected [[Mean sojourn time|dynamical lifetime]] is estimated to be about 10&nbsp;million years.<ref name="Chirikov1989"/> The dynamics of its orbit can be approximately described by a two-dimensional [[symplectomorphism|symplectic map]], known as the [[Kepler map]], a solution to the [[restricted three-body problem]] for highly eccentric orbits.<ref name="Chirikov1989"/><ref name="Lages2018"/> Based on records from the 1910 apparition, [[David Hughes (astronomer)|David Hughes]] calculated in 1985 that Halley's nucleus has been reduced in mass by 80 to 90% over the last 2,000 to 3,000 revolutions, and that it will most likely disappear completely after another 2,300 perihelion passages.<ref name="Hughes1985"/> More recent work suggests that Halley will evaporate, or split in two, within the next few tens of thousands of years, or will be ejected from the Solar System within a few hundred thousand years.<ref name="Williams2015"/><!-- added this because it summarises jewitt2002 which is very technical and hard to read--><ref name="jewitt2002"/>

==Structure and composition==
[[File:Comet Halley close up-cropped.jpg|thumb|right|The nucleus of Halley's Comet, imaged by the [[Giotto (spacecraft)|''Giotto'']] probe on 14{{nbsp}}March 1986. The dark colouration of the nucleus can be observed, as well as the jets of dust and gas erupting from its surface.|alt=A large, black, rock-like structure is visible amid an onrushing cloud of dust. A stream of brilliant white arcs up from the left.]]
The [[Giotto (spacecraft)|''Giotto'']] and ''[[Vega program|Vega]]'' missions gave planetary scientists their first view of Halley's surface and structure. The [[Comet nucleus|nucleus]] is a conglomerate of [[Volatile (astrogeology)|ices]] and [[dust]], often referred to as a "dirty snowball".<ref name="Delehanty"/> Like all comets, as Halley nears the Sun, its volatile compounds (those with low boiling points, such as [[water]], [[carbon monoxide]], [[carbon dioxide]] and other ices) begin to [[Sublimation (chemistry)|sublimate]] from the surface.<ref name="graw"/> This causes the comet to develop a [[Coma (cometary)|coma]], or atmosphere, at distances up to {{convert|230000|km}} from the nucleus.<ref name="Altwegg1993"/> [[Sublimation (phase transition)|Sublimation]] of this dirty ice releases dust particles, which travel with the gas away from the nucleus. Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths, a phenomenon known as [[fluorescence]], whereas dust particles [[scattering|scatter]] the solar light. Both processes are responsible for making the coma visible.<ref name="Delehanty"/> As a fraction of the gas molecules in the coma are [[ionization|ionised]] by the solar [[ultraviolet radiation]],<ref name="Delehanty"/> pressure from the [[solar wind]], a stream of charged particles emitted by the Sun, pulls the coma's ions out into a long [[Comet tail|tail]], which may extend more than 100&nbsp;million&nbsp;kilometres into space.<ref name="graw"/><ref name="Biermann1958"/> Changes in the flow of the solar wind can cause [[disconnection event]]s, in which the tail completely breaks off from the nucleus.<ref name="Brandt1987"/>

Despite the vast size of its coma, Halley's nucleus is relatively small: barely {{convert|15|km}} long, {{convert|8|km}} wide and perhaps {{convert|8|km}} thick.<ref name="Keller1987"/><ref name="Reitsema"/> Based on a reanalysis of images taken by the ''Giotto'' and ''Vega'' spacecraft, Lamy et al. determined an [[mean diameter|effective diameter]] of {{convert|11|km}}.<ref name="Lamy2004"/> Its shape has been variously compared to that of a [[peanut]], a [[potato]], or an [[avocado]].<ref name="Mendis1986"/> Its mass is roughly 2.2{{E-sp|14}}&nbsp;kg,<ref name="mass"/> with an average density of about {{convert|0.55|g/cm3|oz/cuin}}.<ref name="situ"/> The low density indicates that it is made of a large number of small pieces, held together very loosely, forming a structure known as a [[rubble pile]].<ref name="density"/> Ground-based observations of coma brightness suggested that Halley's [[rotation period]] was about 7.4 days. Images taken by the various spacecraft, along with observations of the jets and shell, suggested a period of 52&nbsp;hours.<ref name="situ"/><ref name="BriceHoover2004"/> Given the irregular shape of the nucleus, Halley's rotation is likely to be complex.<ref name="graw"/> The flyby images revealed an extremely varied topography, with hills, mountains, ridges, depressions, and at least one crater.<ref name="situ"/>

Halley's day side (the side facing the Sun) is far more active than the night side.<ref name="situ"/> Spacecraft observations showed that the gases ejected from the nucleus were 80% water vapour, 17% carbon monoxide and 3–4% carbon dioxide,<ref name="Woods1986"/> with traces of hydrocarbons<ref name="Chyba1987"/> although more recent sources give a value of 10% for carbon monoxide and also include traces of [[methane]] and [[ammonia]].<ref name="ESA_2006"/> The dust particles were found to be primarily a mixture of carbon–hydrogen–oxygen–nitrogen (CHON) compounds common in the outer Solar System, and silicates, such as are found in terrestrial rocks.<ref name="graw"/> The dust particles ranged in size down to the [[LOQ|limits of detection]] (≈0.001&nbsp;μm).<ref name="post"/> The ratio of [[deuterium]] to [[hydrogen]] in the water released by Halley was initially thought to be similar to that found in Earth's ocean water, suggesting that Halley-type comets may have delivered water to Earth in the distant past. Subsequent observations showed Halley's deuterium ratio to be far higher than that found in Earth's oceans, making such comets unlikely sources for Earth's water.<ref name="graw"/>

''Giotto'' provided the first evidence in support of [[Fred Whipple]]'s "dirty snowball" hypothesis for comet construction; Whipple postulated that comets are icy objects warmed by the Sun as they approach the inner Solar System, causing ices on their surfaces to [[Sublimation (phase transition)|sublime]] (change directly from a solid to a gas), and jets of volatile material to burst outward, creating the coma. ''Giotto'' showed that this model was broadly correct,<ref name="graw"/> though with modifications. Halley's [[albedo]], for instance, is about 0.04, meaning that it reflects only 4% of the sunlight hitting it &ndash; about what one would expect for coal.<ref name="Weaver1997"/> Thus, despite astronomers predicting that Halley would have an albedo of about 0.17 (roughly equivalent to bare soil), Halley's Comet is in fact pitch black.<ref name="Belton1982"/> The "dirty ices" on the surface sublime at temperatures between {{convert|170|K|°C}} in sections of higher albedo to {{convert|220|K|°C}} at low albedo; ''[[Vega 1]]'' found Halley's surface temperature to be in the range {{convert|300|–|400|K|°C}}. This suggested that only 10% of Halley's surface was active, and that large portions of it were coated in a layer of dark dust that retained heat.<ref name="post"/> Together, these observations suggested that Halley was in fact predominantly composed of non-[[Volatile (astrogeology)|volatile]] materials, and thus more closely resembled a "snowy dirtball" than a "dirty snowball".<ref name="situ"/><ref name="NASA_explore"/>

==History==
===Before 1066===
{{multiple image|header=Early descriptions of Halley's comet|perrow=2|total_width=350|image_gap=5
|image1=Chinese report of Halley's Comet apparition in 240 BC from the Shiji (史記).jpg
|image2=Babylonian tablet recording Halley's comet.jpg
|image3=Paris1337_Horayot_10a.png
|image4=Chronicle of Zuqnin (Vat.sir.162), fol.136v (comet excerpt).jpg
|image5=Annals of Ulster (Trinity College Dublin's MS 1282), year 912.jpg
|footer=From left to right, top to bottom:<br />'''1.''' Report of Halley's Comet by Chinese astronomers in 240{{nbsp}}BC (''[[Records of the Grand Historian|Shiji]]'');<br />'''2.''' Observation of Halley's Comet, recorded in [[Cuneiform script|cuneiform]] on a clay tablet between 22 and 28 September 164{{nbsp}}BC, [[Babylon]], Iraq;<br />'''3.''' Possible record of Halley's Comet's 66{{nbsp}}AD appearance in the [[Talmud]] (b. [[Horayot#Aggada|Horayot]] 10a);<br />'''4.''' The [[Zuqnin Chronicle]]'s mention of Halley's Comet in 760{{nbsp}}AD, with an illustration that includes the relative positions of [[Aries (constellation)|Aries]], [[Mars]] and [[Saturn]] in the sky;<br />'''5.''' The [[Annals of Ulster]]'s entry for the year 912{{nbsp}}AD, ending with ''Cometis apparuit'' ("a comet appeared").}}

Due to its intrinsic brightness, about one eighth of all comet sightings mentioned in historic records belong to Halley's Comet.<ref name="hughes1987"/> The first certain appearance of Halley's Comet in the historical record is a description from 240&nbsp;BC, in the Chinese chronicle ''[[Records of the Grand Historian]]'' or ''Shiji'', which describes a comet that appeared in the east and moved north.{{sfn|Kronk|1999|p=6}} The only surviving record of the 164&nbsp;BC apparition is found on two fragmentary Babylonian tablets, which were rediscovered in August 1984 in the collection of the [[British Museum]].<ref name="Stephenson1985"/><ref name="Walker1985"/>

The apparition of 87&nbsp;BC was recorded in Babylonian tablets which state that the comet was seen "day beyond day" for a month.<ref name="Stephenson1985"/> This appearance may be recalled in the representation of [[Tigranes the Great]], an [[Armenia]]n king who is depicted on coins with a crown that features, according to [[Vahe Gurzadyan]] and R. Vardanyan, "a star with a curved tail [that] may represent the passage of Halley's Comet in 87&nbsp;BC." Gurzadyan and Vardanyan argue that "Tigranes could have seen Halley's Comet when it passed closest to the Sun on August 6 in 87&nbsp;BC" as the comet would have been a "most recordable event".<ref name="Gurzadyan2004"/><ref>{{Cite news|url=https://www.abc.net.au/science/news/stories/s1110824.htm|title=Halley's comet portrayed on ancient coin|first=Heather|last=Catchpole|publisher=[[Australian Broadcasting Corporation]]|date=19 May 2004|access-date=16 June 2025|url-status=live|archive-url=https://web.archive.org/web/20040523022441/https://www.abc.net.au/science/news/stories/s1110824.htm|archive-date=23 May 2004}}</ref>

The apparition of 12&nbsp;BC was recorded in the ''[[Book of Han]]'' by [[Chinese astronomy|Chinese astronomers]] of the [[Han dynasty]] who tracked it from August through October.<ref name="kronk"/> It passed within 0.16&nbsp;au of Earth.<ref name="greatcomets"/> According to the Roman historian [[Cassius Dio]], a comet appeared suspended over Rome for several days portending the death of [[Marcus Vipsanius Agrippa]] in that year.<ref name="Chambers"/> Halley's appearance in 12&nbsp;BC, only a few years distant from the conventionally assigned [[Chronology of Jesus#Year of birth|date of the birth of Jesus Christ]], has led some [[theologian]]s and astronomers to suggest that it might explain the biblical story of the [[Star of Bethlehem]]. There are other explanations for the phenomenon, such as [[planetary conjunction]]s, and there are also records of other comets that appeared closer to the date of Jesus's birth.<ref name="Humphreys1995"/>

If [[Joshua ben Hananiah|Yehoshua ben Hananiah]]'s reference in the ''[[Talmud]]'' to "a star which arises once in seventy years and misleads the sailors"<ref name="Horayot10a"/> refers to Halley's Comet, he can only have witnessed the 66&nbsp;AD appearance.<ref name="Ne'eman1983"/> Another possible reference to the same apparition is also found in the writings of the Jewish historian [[Josephus]],<ref name="Jaroff1985" /> who described several portents visible over Jerusalem shortly before the outbreak of the [[First Jewish–Roman War]]. He reported that "there was a star resembling a sword, which stood over the city, and a comet, that continued a whole year,"<ref>''The Jewish War'', VI, 289</ref><ref name="Josephus" />{{Efn|[[William Whiston]]: "Whether Josephus means that this star was different from that comet which lasted a whole year, I cannot certainly determine. His words most favour their being different one from another."}} events that were interpreted as omens of the [[Siege of Jerusalem (70 CE)|city's destruction]] in 70 AD.<ref name="Horowitz1996" /><ref>{{Cite journal |last=Horowitz |first=Wayne |date=1996 |title=Halley's Comet and Judaean Revolts Revisited |journal=The Catholic Biblical Quarterly |volume=58 |issue=3 |pages=456–459 |jstor=43722716 |issn=0008-7912}}</ref><ref>{{Cite journal |last=Vette |first=Nathanael |date=2023-12-01 |title=The Omens at Jesus's Death (Mark 15:33–39) and the Divine Abandonment of the Temple before Its Destruction in 70 CE |journal=Journal of Biblical Literature |language=en |volume=142 |issue=4 |pages=658–659 |doi=10.15699/jbl.1424.2023.6 |issn=0021-9231}}</ref>

The 141&nbsp;AD apparition was recorded in Chinese chronicles, with observations of a bluish white comet on 27 March and 16, 22 and 23 April.<ref name="Ravené1897"/> The early Tamil bards of southern India (c. 1st - 4th century CE) also describe a certain relatable event.<ref name=":02">{{cite book |last1=Aiyar |first1=K. G. Sesha |url=https://archive.org/details/in.ernet.dli.2015.277483 |title=Chera Kings of the Sangam Period |publisher=Luzac and Co. |year=1937 |isbn= |location=London |pages=63–66 |chapter=Yanaik-kat-Sey Mantaran-Ceral }}</ref>

The 374&nbsp;AD and 607 approaches each came within 0.09&nbsp;[[astronomical unit|au]] of Earth.<ref name="greatcomets"/> The 451&nbsp;AD apparition was said to herald the defeat of [[Attila the Hun]] at the [[Battle of Chalons]].<ref name="Schultheis"/><ref name="Kronk2009"/>

The 684&nbsp;AD apparition was reported in Chinese records as the "broom star".<ref name="art"/>

The 760 AD apparition was recorded in the ''[[Zuqnin Chronicle]]'''s entry for ''iyyōr'' 1071 [[:en:Seleucid era|SE]] (May 760 [[:en:Anno Domini|AD]]), calling it a "white sign":<ref name="Neuhäuser2021"/>

{{blockquote|
text=The year [SE] one thousand seventy one (AD 759/760).
In the month of ''iyyōr'' (May) a white sign was seen in the sky,
before early twilight, in the north-east [quarter],
in the Zodiac [sign] which is called Aries, to the north from these three stars in it, which are very shining.
And it resembled in its shape a broom [...]
And the sign itself remained for fifteen nights, until dawn of the feast of [[Pentecost]].
|source=''Zuqnin Chronicle'', fol.136v; Neuhäuser et al. (trans.)
}}

In 837 AD, Halley's Comet may have passed as close as {{convert|0.03|AU|e6mi e6km|abbr=off}} from [[Earth]], by far its closest approach.<ref name="Horizons837AD"/><ref name="greatcomets"/> Its tail may have stretched 60&nbsp;[[degree (angle)|degrees]] across the sky. It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire, and the Middle East;<ref name="kronk"/> Emperor [[Louis the Pious]] observed this appearance and devoted himself to prayer and penance, fearing that "by this token a change in the realm and the death of a prince are made known."<ref name="Cabaniss1961"/>

In 912 AD, Halley is recorded in the ''[[Annals of Ulster]]'', which states "A dark and rainy year. A comet appeared."<ref name="annals_of_ulster"/>

===1066===
[[File:Comete Tapisserie Bayeux.jpg|thumb|upright=1.5|Halley's Comet in 1066 depicted on the [[Bayeux Tapestry]]]]
In 1066, the comet was seen in England and thought to be an [[omen]]: later that year [[Harold II of England]] died at the [[Battle of Hastings]] and [[William the Conqueror]] claimed the throne. The comet is represented on the [[Bayeux Tapestry]] and described in the [[Bayeux Tapestry tituli#32|tituli]] as a star. Surviving accounts from the period describe it as appearing to be four times the size of [[Venus]], and shining with a light equal to a quarter of that of the [[Moon]]. Halley came within 0.10&nbsp;[[Astronomical unit|au]] of Earth at that time.<ref name="greatcomets"/>

This appearance of the comet is also noted in the ''[[Anglo-Saxon Chronicle]]''. [[Eilmer of Malmesbury]] may have seen Halley in 989 and 1066, as recorded by [[William of Malmesbury]]:

<blockquote>Not long after, a comet, portending (they say) a change in governments, appeared, trailing its long flaming hair through the empty sky: concerning which there was a fine saying of a monk of our monastery called Æthelmær. Crouching in terror at the sight of the gleaming star, "You've come, have you?", he said. "You've come, you source of tears to many mothers. It is long since I saw you; but as I see you now you are much more terrible, for I see you brandishing the downfall of my country."<ref name="William">William of Malmesbury; ''Gesta regum Anglorum / The history of the English Kings'', edited and translated by Mynors, R. A. B.; Thomson, R. M.; and Winterbottom, M.; 2 vols., Oxford Medieval Texts (1998–99), p. 121</ref></blockquote>

The Irish ''[[Annals of the Four Masters]]'' recorded the comet as "A star [that] appeared on the seventh of the [[Calends]] of May, on Tuesday after Little Easter, than whose light the brilliance or light of The Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards."<ref name="annals_of_the_four_masters"/> [[Chaco Culture National Historical Park|Chaco]] [[Native Americans in the United States|Native Americans]] in [[New Mexico]] may have recorded the 1066 apparition in their petroglyphs.<ref name="Brazil2005"/>

The Italo-Byzantine chronicle of [[Lupus Protospatharius|Lupus the Protospatharios]] mentions that a "comet-star" appeared in the sky in the year 1067 (the chronicle is erroneous, as the event occurred in 1066, and by Robert he means William).

<blockquote>The Emperor [[Constantine Ducas]] died in the month of May, and his son Michael received the Empire. And in this year there appeared a comet star, and the Norman count Robert [sic] fought a battle with Harold, King of the English, and Robert was victorious and became king over the people of the English.<ref name="Lupus"/></blockquote>

The Armenian chronicler, [[Matthew of Edessa]] also noted the appearance of the comet, and its coincidence with a Turkic invasion saying:
<blockquote> "At the beginning of the year 515 of the Armenian  era [March 5, 1066-March 4, 1067] a comet appeared out of the  eastern portion of the sky and traveled in a westerly direction. It appeared for one month and then disappeared. A  number of days after this, it reappeared for one month and  then disappeared. A number of days after this, it reappeared  in the western portion of the sky at night; many who saw it  said that it was the same comet which had appeared in the  eastern portion before. During these times, the infidels  marched forth and ravaged all of Armenia, consuming all the  faithful by the sword and enslavement."<ref>"The Chronicle of Matthew of Edessa: Translated From the Original Armenian, With a Commentary and Introduction" by Ara Edmond Dosturian</ref> </blockquote>

===1145–1378===
[[File:Giotto - Scrovegni - -18- - Adoration of the Magi.jpg|thumb|upright=1.3|The ''[[Adoration of the Magi]]'' (circa 1305) by [[Giotto]], who may have modelled the [[Star of Bethlehem]] on Halley's Comet, which had been sighted 4 years before this picture was painted.|alt=The wise men and several animals cluster around the baby Jesus, while a comet-like object streaks overhead]]

The 1145 apparition may have been recorded by the monk [[Eadwine Psalter|Eadwine]].<ref name="Olson1979"/>

According to legend, [[Genghis Khan]] was inspired to turn his conquests toward Europe by the westward-seeming trajectory of the 1222 apparition.<ref name="Johnson1997"/><ref name="Cook2008"/> In Korea, the comet was reportedly visible during the daylight on 9 September 1222.<ref name="Choi2017"/> In Vietnam, the comet was recorded visible in the south-west direction in August (September in solar calendar).<ref>{{cite book |title=Đại Việt sử lược, book 3 |url=https://cvdvn.net/wp-content/uploads/2018/03/dai-viet-su-luoc-khuyet-danh.pdf |page=106 |year=2001 |quote="Năm Nhâm Ngọ (năm 1222- ND) là năm Kiến Gia thứ 12:Mùa thu, tháng 8 sao chổi xuất hiện ở Phương Tây Nam." |language=vi}}</ref> 

The 1301 apparition was visually spectacular, and may be the first that resulted in convincing portraits of a particular comet. The [[Florence (Italy)|Florentine]] chronicler [[Giovanni Villani]] wrote that the comet left "great trails of fumes behind", and that it remained visible from September 1301 until January 1302.{{efn|There are doubts about the latter date. It is generally accepted that the comet was visible from about mid September until about early November.}}<ref name="art"/> It was seen by the artist [[Giotto|Giotto di Bondone]], who represented the [[Star of Bethlehem]] as a fire-coloured comet in the [[Nativity of Jesus in art|Nativity]] section of his [[Scrovegni Chapel|Arena Chapel]] cycle, completed in 1305. Giotto's depiction includes details of the coma, a sweeping tail, and the central condensation. According to the [[art historian]] [[Roberta Olson]], it is much more accurate than other contemporary descriptions, and was not equaled in painting until the 19th century.<ref name="Olson1979"/><ref name="art"/> Olson's identification of Halley's Comet in Giotto's ''Adoration of the Magi'' is what inspired the [[European Space Agency]] to name their mission to the comet ''Giotto'', after the artist.<ref name="asteroid"/>

Halley's 1378 appearance is recorded in the ''Annales Mediolanenses''<ref>''Rerum Italicarum Scriptores'', ed. Ludovico Antonio Muratori (Milan, 1730) v. 16 col. 770.</ref> as well as in East Asian sources.{{sfn|Kronk|1999|pp=253–255}}

===1456===

In 1456, the year of Halley's next apparition, the [[Ottoman Empire]] invaded the [[Kingdom of Hungary]], culminating in the [[Siege of Belgrade (1456)|siege of Belgrade]] in July of that year. In a [[papal bull]], [[Pope Callixtus III]] ordered special prayers be said for the city's protection. In 1470, the [[Renaissance humanism|humanist]] scholar [[Bartolomeo Platina]] wrote in his ''{{interlanguage link|Lives of the Popes (Platina)|lt=Lives of the Popes|la|Vitae Pontificum (Platina)}}'' that,<ref name="Emerson"/>

<blockquote>A hairy and fiery star having then made its appearance for several days, the mathematicians declared that there would follow grievous pestilence, dearth and some great calamity. Calixtus, to avert the wrath of God, ordered supplications that if evils were impending for the human race He would turn all upon the Turks, the enemies of the Christian name. He likewise ordered, to move God by continual entreaty, that notice should be given by the bells to call the faithful at midday to aid by their prayers those engaged in battle with the Turk.</blockquote>

Platina's account is not mentioned in official records. In the 18th century, a Frenchman further embellished the story, in anger at the Church, by claiming that the Pope had "excommunicated" the comet, though this story was most likely his own invention.<ref name="Botley1971"/>

Halley's apparition of 1456 was also witnessed in [[Kashmir]] and depicted in great detail by Śrīvara, a Sanskrit poet and biographer to the Sultans of Kashmir. He read the apparition as a cometary portent of doom foreshadowing the imminent fall of [[Zayn al-Abidin (sultan of Kashmir)|Sultan Zayn al-Abidin]] (AD 1418/1420–1470).<ref>[[Walter Slaje|Slaje, Walter]]; inter alia, realia: "An Apparition of Halley's Comet in Kashmir observed by Śrīvara in AD 1456" in Steiner, Roland (ed.); ''Highland Philology: Results of a Text-Related Kashmir Panel at the 31st DOT, Marburg 2010'', Studia Indologica Universitatis Halensis, 4, Halle 2012: 33–48</ref>

After witnessing a bright light in the sky which most historians have identified as Halley's Comet, [[Zara Yaqob]], Emperor of [[Ethiopia]] from 1434 to 1468, founded the city of [[Debre Berhan]] (tr. City of Light) and made it his capital for the remainder of his reign.<ref>The founding of Debre Berhan is described in the ''Ethiopian Royal Chronicles'' (Pankhurst, Richard; Oxford University Press, Addis Ababa, 1967, pp. 36–38).</ref>

===1531–1759===
[[File:Astronomicum Caesareum (1540), p.89v (comet illustration).jpg|thumb|Illustration of the 1531 appearance in Petrus Apianus' [[Astronomicum Caesareum]], noting that a comet's tail always points away from the sun]]

In the [[Sikh]] scriptures of the [[Guru Granth Sahib]], the founder of the faith [[Guru Nanak]] makes reference to "''a long star that has risen''" at Ang 1110, and it is believed by some Sikh scholars to be a reference to Halley's appearance in 1531.<ref name="Kapoor2017"/>

Halley's periodic returns have been subject to scientific investigation since the 16th century. [[Petrus Apianus]] and [[Girolamo Fracastoro]] described the comet's visit in 1531, with the former even including graphics in his publication. Through his observations, Apianus was able to prove that a comet's tail always points away from the Sun.<ref name="Barker2008"/> The three apparitions from 1531 to 1682 were noted by Edmond Halley, enabling him to predict it would return.{{sfn|Grier|2005|pp=11–25}} One key breakthrough occurred when Halley talked with Newton about his ideas of the laws of motion. Newton also helped Halley get John Flamsteed's data on the 1682 apparition.<ref name="1985JHA"/> By studying data on the 1531, 1607, and 1682 comets, he came to the conclusion these were the same comet, and presented his findings in 1696.<ref name="1985JHA"/>

One difficulty was accounting for variations in the comet's orbital period, which was over a year longer between 1531 and 1607 than it was between 1607 and 1682.{{sfn|Sagan|Druyan|1985|p=57}} Newton had theorised that such delays were caused by the gravity of other comets, but Halley found that Jupiter and Saturn would cause the appropriate delays.{{sfn|Sagan|Druyan|1985|p=57}} In the decades that followed, more refined mathematics would be worked on, notable by Paris Observatory; the work on Halley also provided a boost to Newton and Kepler's rules for celestial motions.<ref name="1985JHA"/> (See also [[#Computation of orbit|computation of orbit]].)

===1835===
At [[Markree Observatory]] in Ireland, [[Edward Joshua Cooper]] used a [[Robert-Aglaé Cauchoix|Cauchoix of Paris]] lens telescope with an aperture of {{convert|13.3|inch|mm|order=flip}} to sketch Halley's comet in 1835.<ref name="Abrahams2009"/> The same apparition was sketched by German astronomer [[Friedrich Wilhelm Bessel]].<ref name="Smithsonian1835"/> Observations of streams of vapour prompted Bessel to propose that the [[jet force]]s of evaporating material could be great enough to significantly alter a comet's orbit.{{sfn|Sagan|Druyan|1985|p=117}}

{{multiple image
|align=right
|direction=vertical
|width=200
|header=Illustrations of prior comet appearances in the January 1910 ''[[Popular Science|Popular Science Monthly]]'' magazine
|image1=PSM V76 D017 Halley comet in 1682 (horizontal).png
|caption1=1682
|image2=PSM V76 D017 Halley comet in 1759 (horizontal).png
|caption2=1759
|image3=PSM V76 D018 Halley comet in 1835.png
|caption3=1835
}}
An interview in 1910, of someone who was a teenager at the time of the 1835 apparition had this to say:<ref name="Todd Saw Halley's Comet in 1835"/>

{{blockquote|When the comet was first seen, it appeared in the western sky, its head toward the north and tail towards the south, about horizontal and considerably above the horizon and quite a distance south of the Sun. It could be plainly seen directly after sunset every day, and was visible for a long time, perhaps a month ...}}

They go on to describe the comet's tail as being more broad and not as long as the comet of 1843 they had also witnessed.<ref name="Todd Saw Halley's Comet in 1835"/>

Famous astronomers across the world made observations starting August 1835, including Struve at Dorpat observatory, and Sir John Herschel, who made of observations from the Cape of Good Hope.<ref name=":0"/> In the United States telescopic observations were made from [[Yale College]].<ref name=":0"/> The new observations helped confirm early appearances of this comet including its 1456 and 1378 apparitions.<ref name=":0"/>

At Yale College in Connecticut, the comet was first reported on 31 August 1835 by astronomers D. Olmstead and E. Loomis.<ref name=":2"/> In Canada reports were made from Newfoundland and also Quebec.<ref name=":2"/> Reports came in from all over by later 1835, and often reported in newspapers of this time in Canada.<ref name=":2"/>

Several accounts of the 1835 apparition were made by observers who survived until the 1910 return, where increased interest in the comet led to them being interviewed.<ref name=":2"/>

The time to Halley's return in 1910 would be only 74.42 years, one of the shortest known periods of its return, which is calculated to be as long as 79 years owing to the effects of the planets.<ref name="NASA_1P-explore"/>

At [[Paris Observatory]] Halley's Comet 1835 apparition was observed with a Lerebours telescope of {{convert|24.4|cm|in|abbr=on}} aperture by the astronomer [[François Arago]].{{sfn|Lequeux|2015|p=180}} Arago recorded polarimetric observations of Halley, and suggested that the tail might be sunlight reflecting off a sparsely distributed material; he had earlier made similar observations of [[Comet Tralles]] of 1819.<ref name="Levasseur-Regourd2019"/>

===1910===
{{multiple image
|align=right
|direction=vertical
|width=200
|image_gap=10
|image1=Halley's comet 1910 (cropped).jpg
|caption1=Halley's Comet in April 1910, photographed from [[Arequipa]], Peru
|image2=Halley's Comet - May 29 1910.jpg
|caption2=A photograph of Halley's Comet taken at [[Yerkes Observatory]] on 29 May 1910
|alt2=Black-and-white picture of the comet, its nucleus brilliant white, and its tail very prominent, moving up and to the right
}}
The 1910 approach, which came into naked-eye view around 10 April<ref name="greatcomets"/> and came to perihelion on 20 April,<ref name="greatcomets"/> was notable for several reasons: it was the first approach of which photographs exist, and the first for which [[spectroscopic]] data were obtained.<ref name="post"/> Furthermore, the comet made a relatively close approach of 0.15 au,<ref name="greatcomets"/> making it a spectacular sight. Indeed, on 19 May, Earth actually passed through the tail of the comet.<ref name="Ridpath"/><ref name="pfizer"/> One of the substances discovered in the tail by spectroscopic analysis was the toxic gas [[cyanogen]],<ref name="NYTimes_19100208"/> which led press to misquote the astronomer [[Camille Flammarion]] by stating he claimed that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet".{{sfnm|Goodrich|2023|1p=83|Goodrich|2023|2p=238}}<ref name="smith"/> Despite reassurances from scientists that the gas would not inflict harm on Earth,<ref name="smith"/> the damage had already been done with members of the public [[panic buying]] gas masks and [[Quackery|quack]] "anti-comet pills".{{sfn|Goodrich|2023|p=188}}

The comet added to the unrest in China on the eve of the [[Xinhai Revolution]] that would end the [[Qing dynasty|last dynasty]] in 1911.<ref name="TingChen2022"/> As James Hutson, a missionary in [[Sichuan]] Province at the time, recorded:

<blockquote>"The people believe that it indicates calamity such as war, fire, pestilence, and a change of dynasty. In some places on certain days the doors were unopened for half a day, no water was carried and many did not even drink water as it was rumoured that pestilential vapour was being poured down upon the earth from the comet."<ref name="Hutson1921"/></blockquote>

The 1910 visitation coincided with a visit from [[Hedley Churchward]], the first known English Muslim to make the Haj pilgrimage to [[Mecca]].<ref name="Rosenthal1931"/>

The comet was used in an advertising campaign of [[Le Bon Marché]], a well-known department store in Paris.<ref name="Bibliothèque_numérique"/>

The comet was also fertile ground for [[hoaxes]]. One that reached major newspapers claimed that the Sacred Followers, a supposed [[Oklahoma]] religious group, attempted to sacrifice a virgin to ward off the impending disaster, but were stopped by the police.<ref name="Johnson1997b"/>

American satirist and writer [[Mark Twain]] was born on 30 November 1835, exactly two weeks after the comet's [[Perihelion and aphelion|perihelion]]. In his autobiography, published in 1909, he said,

<blockquote>I came in with Halley's comet in 1835. It is coming again next year, and I expect to go out with it. It will be the greatest disappointment of my life if I don't go out with Halley's comet. The Almighty has said, no doubt: "Now here are these two unaccountable freaks; they came in together, they must go out together."<ref name="Paine1912"/><ref name="Metcalf2009"/></blockquote>

Twain died on 21 April 1910, the day following the comet's subsequent perihelion.<ref name="Cleere1985"/><ref name="Chautauquan1910"/> The 1985 fantasy film ''[[The Adventures of Mark Twain (1985 film)|The Adventures of Mark Twain]]'' was inspired by the quotation.<ref name="TwainMovie"/>

Halley's 1910 apparition is distinct from the [[Great January Comet of 1910|Great Daylight Comet of 1910]], which surpassed Halley in brilliance and was visible in broad daylight for a short period, approximately four months before Halley made its appearance.<ref name="Comet1910"/><ref name="Bortle1998"/>

===1986===
{{multiple image
| align             = right
| direction         = vertical
| width             = 200
| image_gap         = 10
| image1            = Comethalley-21mar1986.jpg
| caption1          = Halley's Comet as seen on 21 March 1986
| image2            = Animation of 1P／Halley orbit - 1986 apparition.gif
| caption2          = Animation of 1P/Halley orbit - 1986 apparition<br />{{legend2|magenta|1P/Halley}}{{·}}{{legend2|Royalblue|Earth}}{{·}}{{legend2|Yellow|Sun}}
| image3            = Halley path 1986.png
| caption3          = Daily motion across sky during the 1986 passage of Halley's Comet. The section of the ecliptic from [[Capricornus (constellation)|Capricornus]] on the left to [[Leo (constellation)|Leo]] on the right is shown.
}}

The 1986 apparition of Halley's Comet was the least favourable on record. In February 1986, the comet and the Earth were on opposite sides of the Sun, creating the worst possible viewing circumstances for Earth observers during the previous 2,000 years.<ref name="Broughton1979"/> Halley's closest approach was 0.42 au.<ref name="JPL_summary"/> Additionally, increased [[light pollution]] from [[urbanisation]] caused many people to fail in attempts to see the comet. With the help of binoculars, observation from areas outside cities was more successful.<ref name="Australian_Astronomy"/> Further, the comet appeared brightest when it was almost invisible from the northern hemisphere in March and April 1986,<ref name="Ocala"/> with best opportunities occurring when the comet could be sighted close to the horizon at dawn and dusk, if not obscured by clouds.

The approach of the comet was first detected by astronomers [[David C. Jewitt]] and G. Edward Danielson on 16 October 1982 using the 5.1&nbsp;m [[Hale Telescope]] at [[Mount Palomar Observatory|Mount Palomar]] and a [[CCD camera]].<ref name="Recovery_ESA"/>

The first visual observation of the comet on its 1986 return was by an amateur astronomer, Stephen James O'Meara, on 24 January 1985. O'Meara used a home-built {{convert|24|in|mm|order=flip|adj=on}} telescope on top of [[Mauna Kea]] to detect the [[apparent magnitude|magnitude]] 19.6 comet.<ref name="Jan24"/> The first to observe Halley's Comet with the naked eye during its 1986 apparition were Stephen Edberg (then serving as the coordinator for amateur observations at the [[NASA]] [[JPL|Jet Propulsion Laboratory]]) and Charles Morris on 8 November 1985.<ref name="Naked_eye_NYT"/>

The 1986 apparition gave scientists the opportunity to study the comet closely, and several probes were launched to do so. The Soviet ''Vega 1'' probe began returning images of Halley on 4 March 1986, captured the first-ever image of its [[Comet nucleus|nucleus]],<ref name="situ"/> and made its flyby on 6 March. It was followed by the ''[[Vega 2]]'' probe, making its flyby on 9 March. On 14 March, the ''Giotto'' space probe, launched by the [[European Space Agency]], made the closest pass of the comet's nucleus.<ref name="situ"/> There also were two Japanese probes, [[Suisei (spacecraft)|''Suisei'']] and ''[[Sakigake]]''. Unofficially, the numerous probes became known as the [[Halley Armada]].<ref name="Suisei2008"/>

Based on data retrieved by the largest [[ultraviolet]] space telescope of the time, [[Astron (spacecraft)|''Astron'']], in December 1985, a group of Soviet scientists developed a model of the comet's [[Coma (cometary)|coma]].<ref name="Boyarchuk1986"/> The comet also was observed from space by the ''[[International Cometary Explorer]]'' (ICE). Originally launched as the ''International Sun-Earth Explorer 3'', the spacecraft was renamed, and departed the Sun-Earth {{L1}} [[Lagrangian point]] in 1982 in order to intercept the comets [[21P/Giacobini-Zinner]] and Halley.<ref name="Murdin2000"/> ICE flew through the tail of Halley's Comet, coming within about {{convert|40.2|e6km|e6mi|abbr=unit}} of the nucleus on 28 March 1986.<ref name="ISEE-3"/>{{sfn|Siddiqi|2018|pp=149–150}}

Two U.S. [[Space Shuttle]] missions—[[STS-51-L]] and [[STS-61-E]]—had been scheduled to observe Halley's Comet from [[low Earth orbit]]. The STS-51-L mission carried the ''Shuttle-Pointed Tool for Astronomy'' ([[Spartan Halley]]) satellite, also called the ''Halley's Comet Experiment Deployable'' (HCED).<ref name="Spartan-203"/> The mission to capture the ultraviolet [[Astronomical spectroscopy|spectrum]] of the comet [[Space Shuttle Challenger disaster|ended in disaster]] when the Space Shuttle ''Challenger'' disintegrated in flight, killing all seven astronauts onboard.<ref name="STS-51L"/> Scheduled for March 1986, STS-61-E was a ''Columbia'' mission carrying the ASTRO-1 platform to study the comet,{{sfn|Shayler|Burgess|2007|pp=431–476}} but the mission was cancelled following the ''Challenger'' disaster and ASTRO-1 would not fly until late 1990 on [[STS-35]].<ref name="STS-35"/>

In Japan, the comet was observed by Emperor [[Hirohito]], who was 84.<ref name="Upi1986"/> He had already seen it in 1910 when he was 8.<ref name="Upi1986"/>

===After 1986===
[[File:ESO-Comet Halley at 28 AU-phot-27a-03-fullres.jpg|thumb|right|Halley's Comet observed in 2003 at 28 au from the Sun|alt=Grainy, white-on-black image showing Halley as a barely distinguishable black dot]]

On 12 February 1991, at a distance of {{convert|14.3|au|e6km|abbr=unit}} from the Sun, Halley displayed an outburst that lasted for several months.{{r|Gronkowski2002|graw}} The comet released dust with a total mass of about {{10^|8}} kg, which spread into an elongated cloud roughly {{cvt|374000|km}} by {{cvt|269000|km}} in size.{{r|West1991}} The outburst likely started in December 1990, and then the comet brightened from about magnitude 25 to magnitude 19.{{r|Prialnik1992|Gronkowski2002}} Comets rarely show outburst activity at distances beyond 5 au from the Sun.{{r|Gronkowski2002}} Different mechanisms have been proposed for the outburst, ranging from interaction with the solar wind to a collision with an undiscovered asteroid.{{r|Hughes1991}} The most likely explanation is a combination of two effects, the [[polymerization|polymerisation]] of [[hydrogen cyanide]] and a [[phase transition]] of [[Phases of ice|amorphous water ice]], which raised the temperature of the nucleus enough for some of the more volatile compounds on its surface to sublime.{{r|Gronkowski2002}}

Halley was most recently observed in 2003 by three of the [[Very Large Telescope]]s at Paranal, Chile, when Halley's magnitude was 28.2. The telescopes observed Halley, at the faintest and farthest any comet had ever been imaged, in order to verify a method for finding very faint [[trans-Neptunian object]]s.{{r|ESO2003}} Astronomers are now able to observe the comet at any point in its orbit.{{r|ESO2003}}

On 9 December 2023, Halley's Comet reached the farthest and slowest point in its orbit from the Sun when it was travelling at {{cvt|0.91|km/s|mph}} with respect to the Sun.{{r|Horizons2023}}<ref name=seeker2013>{{Cite web|url=https://www.seeker.com/lets-plan-for-a-rendezvous-with-halleys-comet-1767783657.html|title=Let's Plan For a Rendezvous With Halley's Comet|last=DNews|date=3 September 2013|website=Seeker|access-date=29 October 2019|archive-url=https://web.archive.org/web/20221128171635/https://www.seeker.com/lets-plan-for-a-rendezvous-with-halleys-comet-1767783657.html|archive-date=28 November 2022}}</ref>

=== 2061 ===
[[File:Animation of 1P／Halley orbit - 2061 apparition.gif|thumb|Animation of 1P/Halley orbit - 2061 apparition<br />{{legend2| yellow| Sun}}{{·}}{{legend2| Cyan| Venus}}{{·}}{{legend2| RoyalBlue| Earth}}{{·}}{{legend2| Gold| Jupiter}}{{·}}{{legend2| Magenta| 1P/Halley}}]]
The next perihelion of Halley's Comet is predicted for 28 July 2061,<ref name="Horizons2061"/><ref name="Kinoshita"/> when it will be better positioned for observation than during the 1985–1986 apparition, as it will be on the same side of the Sun as Earth.<ref name="Abrams-Planetarium"/> The closest approach to Earth will be one day after perihelion.<ref name=jpldata/> It is expected to have an [[apparent magnitude]] of −0.3, compared with only +2.1 for the 1986 apparition.<ref name="sten"/> On 9 September 2060, Halley will pass within {{convert|0.98|au|km|abbr=on}} of Jupiter, and then on 20 August 2061 will pass within {{convert|0.0543|au|km|abbr=on}} of Venus.<ref name="jpldata"/>

===2134===
Halley will come to perihelion on 27 March 2134.<ref name="Horizons2134"/><ref name="Kinoshita"/> Then on 7 May 2134, Halley will pass within {{convert|0.092|au|km|abbr=on}} of Earth.<ref name="jpldata"/> Its apparent magnitude is expected to be −2.0.<ref name="sten"/>

===List of apparitions===
Halley's calculations enabled the comet's earlier appearances to be found in the historical record. The following table sets out the [[Comet#Nomenclature|astronomical designations]] for every apparition of Halley's Comet from 240&nbsp;BC, the earliest documented sighting.<ref name="jpldata"/><ref name="icqdes"/>

In the designations, "1P/" refers to Halley's Comet; the first periodic comet discovered. The number represents the year, with negatives representing BC. The letter-number combination indicates which it was of the comets observed for a given segment of the year, divided into 24 equal parts.{{sfn|Schmude|2010|p=3}} The Roman numeral indicates which comet past perihelion it was for a given year, while the lower-case letter indicates which comet it was for a given year overall.<ref name="Marsden1996"/> The perihelion dates farther from the present are approximate, mainly because of uncertainties in the modelling of non-gravitational effects. Perihelion dates of 1531 and earlier are in the [[Julian calendar]], while perihelion dates 1607 and after are in the [[Gregorian calendar]].<ref name="Sitarski1988"/> The perihelion dates for some of the early apparitions (particularly before 837 AD) are uncertain by a couple of days.<ref name="Sitarski1988"/> While Halley's Comet usually peaks at around 0th magnitude, there are indications that the comet got considerably brighter than that in the past.<ref name="Chang1979"/>

{| class="wikitable" style="width:98%;"
|-valign=top
!Return cycle<ref name="Chang1979"/>
!Designation
!Year BC/AD
!Gap (years)
![[Apsis#Time of perihelion|Date of perihelion]]<ref name=MPC/>
!Observation interval<ref name="yeo_p81"/>{{efn|Prior to the [[invention of the telescope]] in the 17th century, this is the time when the comet was visible to the naked eye.}}
!Earth approach<ref name="greatcomets"/>
!Maximum brightness<ref name="Chang1979"/>
!Description<ref name="Ridpath1985"/>
|-
|−29
|1P/−239 K1
|style="white-space:nowrap;"|[[240 BC]]
| –
|30 March
|May – June
|
|
|First confirmed sighting
|-
|−28
|1P/−163 U1
|[[164 BC]]
|76
|17 November?
|October – November
|
|
|Seen by Babylonians
|-
|−27
|1P/−86 Q1
|[[87 BC]]
|77
|2 August
|9 July – 24 August
|
|
|Seen by the Babylonians and Chinese
|-
|−26
|1P/−11 Q1
|[[12 BC]]
|75
|5 October
|26 August – 20 October
|0.16 au
| −5 mag
|Watched by Chinese for two months
|-
|−25
|1P/66 B1
|[[AD 66|66]]
|77
|26 January
|31 January – 10 April
|
| −7 mag
|May be the comet described in [[Josephus]]'s ''[[The Jewish War]]'' as "A comet of the kind called Xiphias, because their tails appear to represent the blade of a sword" that supposedly heralded the destruction of the [[Second Temple]] in 70 AD.<ref name="Chambers" />
|-
|−24
|1P/141 F1
|[[AD 141|141]]
|75
|22 March
|27 March – late April
|
| −4 mag
|Described by the Chinese as bluish-white in colour
|-
|−23
|1P/218 H1
|[[218]]
|77
|17 May
|early May – mid June
|
| −4 mag
|Described by the Roman historian [[Dion Cassius]] as "a very fearful star"
|-
|−22
|1P/295 J1
|[[295]]
|77
|20 April
|1–30 May
|
| −3 mag
|Seen in China, but not spectacular
|-
|−21
|1P/374 E1
|[[374]]
|79
|17 February
|4 March – 2 April
|0.09 au
| −3 mag
|Comet passed 13.5 million kilometres from Earth.
|-
|−20
|1P/451 L1
|[[451]]
|77
|24 June
|10 June – 15 August
|
| −3 mag
|Comet appeared before the defeat of [[Attila|Attila the Hun]] at the [[Battle of Chalons (451)|Battle of Chalons]].
|-
|−19
|1P/530 Q1
|[[530]]
|79
|26 September
|29 August – 23 September
|
| −3 mag
|Noted in China and Europe, but not spectacular
|-
|−18
|1P/607 H1
|[[607]]
|77
|13 March
|March – April
|0.09 au
| −4 mag
|Comet passed 13.5 million kilometres from Earth.
|-
|−17
|1P/684 R1
|[[684]]
|77
|28 October
|September – October
|
| −2 mag
|First known Japanese records of the comet. Attempts have been made to connect an ancient Maya depiction of [[God L]] to the event.{{sfn|Milbrath|1999|p=684}}
|-
|−16
|1P/760 K1
|[[760]]
|76
|22 May
|17 May – mid June
|
| −2 mag
|Seen in China, at the same time as another comet
|-
|−15
|1P/837 F1
|[[837]]
|77
|28 February
|22 March – 28 April
|0.033 au<ref name="Horizons837AD"/>
| −3 mag
|Closest-ever approach to the Earth (5 million km). Tail stretched halfway across the sky. Appeared as bright as Venus.
|-
|−14
|1P/912 J1
|[[912]]
|75
|9 July
|July
|
| −2 mag
|Seen briefly in China and Japan
|-
|−13
|1P/989 N1
|[[989]]
|77
|9 September
|August – September
|
| −1 mag
|Seen in China, Japan, and (possibly) Korea
|-
|−12
|1P/1066 G1
|[[1066]]
|77
|23 March
|3 April – 7 June
|0.10 au
| −4 mag
|Seen for over two months in China. Recorded in England and depicted on the later [[Bayeux tapestry]] which portrayed the events of that year.
|-
|−11
|1P/1145 G1
|[[1145]]
|79
|21 April
|15 April – 6 July
|
| −2 mag
|Depicted on the [[Eadwine Psalter]], with the remark that such "hairy stars" appeared rarely, "and then as a portent"
|-
|−10
|1P/1222 R1
|[[1222]]
|77
|30 September
|3 September – 8 October
|
| −1 mag
|Described by Japanese astronomers as being "as large as the half Moon... Its colour was white but its rays were red"
|-
|−9
|1P/1301 R1
|[[1301]]
|79
|24 October
|1 September – 31 October
|
| −1 mag
|Seen by [[Giotto|Giotto di Bondone]] and included in his painting ''[[Adoration of the Magi|The Adoration of the Magi]]''. Chinese astronomers compared its brilliance to that of the first-magnitude star [[Procyon]].
|-
|−8
|1P/1378 S1
|[[1378]]
|77
|9 November
|26 September – 11 October
|
| −1 mag
|Passed within 10 degrees of the north celestial pole, more northerly than at any time during the past 2000 years. This is the last appearance of the comet for which eastern records are better than Western ones.
|-
|−7
|1P/1456 K1
|[[1456]]
|78
|9 June
|27 May – 8 July
|
| 0 mag
|Observed in Italy by [[Paolo Toscanelli]], who said its head was "as large as the eye of an ox", with a tail "fan-shaped like that of a peacock". Arabs said the tail resembled a Turkish scimitar. Turkish forces attacked Belgrade.
|-
|−6
|1P/1531 P1
|[[1531]]
|75
|25 August
|1 August – 8 September
|
| −1 mag
|Seen by [[Peter Apian]], who noted that its tail always pointed away from the Sun. This sighting was included in Halley's table.
|-
|−5
|1P/1607 S1
|[[1607]]
|76
|27 October
|21 September – 26 October
|
| 0 mag
|Seen by [[Johannes Kepler]]. This sighting was included in Halley's table.
|-
|−4
|1P/1682 Q1
|[[1682]]
|75
|15 September
|15 August – 21 September
|
| 0 mag
|Seen by [[Edmond Halley]] at Islington
|-
|−3
|{{hlist|1P/1758 Y1|1759 I}}
|[[1758]]
|76
|13 March
|25 December 1758 – 22 June 1759
|
| −1 mag
|Return predicted by Halley. First seen by [[Johann Palitzsch]] on 25 December 1758.
|-
|−2
|{{hlist|1P/1835 P1|1835 III}}
|[[1835]]
|77
|16 November
|5 August 1835 – 19 May 1836
|
| 0 mag
|First seen at the Observatory of the [[Roman College]] in August.<ref name="AsNa1836" /> Studied by [[John Herschel]] at the Cape of Good Hope.
|-
|−1
|{{hlist|1P/1909 R1|1910 II|1909c}}
|[[1910]]
|75
|20 April
|25 August 1909 – 16 June 1911
|0.151 au<ref name=jpldata/>
| 0 mag
|Photographed for the first time. Earth passed through the comet's tail on 20 May.
|-
|0
|{{hlist|1P/1982 U1|1986 III|1982i}}
|[[1986]]
|76
|9 February
|Astronomers are now able to observe the comet at every point in its orbit.<ref name="ESO2003" />
|0.417 au
| +2 mag
|Reached [[Perihelion and aphelion|perihelion]] on 9 February, closest to Earth (63 million km) on 10 April. Nucleus photographed by the European space probe [[Giotto (spacecraft)|''Giotto'']] and the Soviet probes ''[[Vega 1]]'' and ''[[Vega 2|2]]''.
|-
|1
|
|[[2061]]
|75
|28 July<ref name="Horizons2061"/><ref name="Kinoshita"/>
|
|0.477 au
|
|Next return with perihelion on 28 July 2061<ref name="Horizons2061"/><ref name="Kinoshita"/> and Earth approach one day later on 29 July 2061<ref name=jpldata/>
|-
|2
|
|2134
|73
|27 March<ref name="Horizons2134"/><ref name="Kinoshita"/>
|
|0.092 au<ref name=jpldata/>
|
|Subsequent return with perihelion on 27 March 2134 and Earth approach on 7 May 2134
|-
|3
|
|2209
|75
|3 February<ref name="Horizons2209"/>
|
|0.515 au<ref name="Horizons2209"/>
|
|Best-fit for February 2209 perihelion passage and April Earth approach

|}
{{Clear}}

==See also==
* {{anl|Kepler orbit}}
* [[List of Halley-type comets]]

==Notes==
{{Notelist}}

==References==
{{Reflist|refs=

<ref name="MPC">{{cite web
| title= 1P/Halley Orbit
| url= https://www.minorplanetcenter.net/db_search/show_object?object_id=1P
| publisher= [[Minor Planet Center]]
| archive-url= https://web.archive.org/web/20220704122451/https://www.minorplanetcenter.net/db_search/show_object?object_id=1P
| access-date= 2022-06-28
| archive-date= 2022-07-04
| url-status= live }} (epoch 451 is 79.29 years)
</ref>

<ref name="Peale1989November">{{Cite journal|first=Stanton J.|last=Peale|author-link=Stanton J. Peale|title=On the density of Halley's comet|journal=[[Icarus (journal)|Icarus]]|volume=82|issue=1|pages=36–49|date=1989|doi=10.1016/0019-1035(89)90021-3|quote=densities obtained by this procedure are in reasonable agreement with intuitive expectations of densities near 1&nbsp;g/cm3, the uncertainties in several parameters and assumptions expand the error bars so far as to make the constraints on the density uniformative&nbsp;... suggestion that cometary nuclei tend to by very fluffy,&nbsp;... should not yet be adopted as a paradigm of cometary physics.|bibcode=1989Icar...82...36P}}</ref>

<ref name="AsNa1836">{{Cite journal|first1=Etienne|last1=Dumouchel|title=Vermischte Nachrichten|journal=[[Astronomische Nachrichten]]|volume=13|issue=1|page=16|date=1836}}</ref>

<ref name="Peale1989">{{Cite journal|first1=Stanton J.|last1=Peale|first2=Jack J.|last2=Lissauer|author-link2=Jack J. Lissauer|title=Rotation of Halley's Comet|journal=Icarus|volume=79|issue=2|pages=396–430|date=1989|doi=10.1016/0019-1035(89)90085-7|bibcode=1989Icar...79..396P}}</ref>

<ref name="dark">{{Cite web|date=29 November 2001|title=Comet Borrelly Puzzle: Darkest Object in the Solar System|publisher=Space.com|first=Robert Roy|last=Britt|url=http://www.meteorite-list-archives.com/2001/nov/0597.html|access-date=16 December 2008|archive-url=https://web.archive.org/web/20140104000957/http://www.meteorite-list-archives.com/2001/nov/0597.html|archive-date=4 January 2014}}</ref>

<ref name="jpldata">{{Cite web|type=11 January 1994 last obs|title=JPL Small-Body Database Browser: 1P/Halley|url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1P&view=OPC|publisher=Jet Propulsion Laboratory|archive-url=https://web.archive.org/web/20150427033624/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1P;orb=0;cov=0;log=0;cad=1|archive-date=27 April 2015|url-status=live|access-date=28 June 2022}}</ref>

<ref name="Kinoshita">{{cite web|title=1P/Halley past, present and future orbital elements|url=http://jcometobs.web.fc2.com/pcmtn/0001p.htm|work=Comet Orbit|first=Kazuo|last=Kinoshita|date=3 October 2003}}</ref>

<ref name="Horizons837AD">{{cite web|title=Horizons Batch for 1P/Halley (90000015) on 837AD-Apr-10|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|type=Earth approach occurs when deldot flips from negative to positive @ 837-Apr-10 12:13|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000015%27&START_TIME=%27837AD-Apr-10%2012:00%27&STOP_TIME=%27837AD-Apr-10%2012:30%27&STEP_SIZE=%271%20minutes%27&QUANTITIES=%2719,20,23%27|archive-url=https://web.archive.org/web/20220630021517/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000015%27&START_TIME=%27837AD-Apr-10+12%3A00%27&STOP_TIME=%27837AD-Apr-10+12%3A30%27&STEP_SIZE=%271+minutes%27&QUANTITIES=%2719%2C20%2C23%27|archive-date=30 June 2022|url-status=live|access-date=29 June 2022}} (SAO/837)</ref>

<ref name="Horizons2023">{{cite web|title=Horizons Batch for 1P/Halley (90000030) on 2023-Dec-09|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|type=Aphelion occurs when rdot flips from positive to negative|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272023-Dec-09%27&STOP_TIME=%272023-Dec-10%27&STEP_SIZE=%271%20hours%27&QUANTITIES=%2719,22%27|archive-url=https://web.archive.org/web/20220701123600/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272023-Dec-09%27&STOP_TIME=%272023-Dec-10%27&STEP_SIZE=%271+hours%27&QUANTITIES=%2719%2C22%27|archive-date=1 July 2022|url-status=live|access-date=1 July 2022}} (JPL#73 Soln.date: 2022-Jun-07)</ref>

<ref name="Horizons2061">{{cite web|title=Horizons Batch for 1P/Halley (90000030) on 2061-Jul-28|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|type=Perihelion occurs when rdot flips from negative to positive @ 2061-Jul-28 17:20 UT|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272061-Jul-28%2017:00%27&STOP_TIME=%272061-Jul-28%2018:00%27&STEP_SIZE=%271%20min%27&QUANTITIES=%2719%27|archive-url=https://web.archive.org/web/20220527191157/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000033%27&START_TIME=%272061-Jul-28%2017:00%27&STOP_TIME=%272061-Jul-28%2018:00%27&STEP_SIZE=%271%20min%27&QUANTITIES=%2719%27|archive-date=27 May 2022|url-status=live|access-date=28 June 2022}} (JPL#73 Soln.date: 2022-Jun-07)</ref>

<ref name="Horizons2134">{{cite web|title=Horizons Batch for 1P/Halley (90000030) on 2134-Mar-27|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|type=Perihelion occurs when rdot flips from negative to positive|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272134-Mar-24%27&STOP_TIME=%272134-Mar-30%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27|archive-url=https://web.archive.org/web/20220628122506/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272134-Mar-24%27&STOP_TIME=%272134-Mar-30%27&STEP_SIZE=%273+hours%27&QUANTITIES=%2719%27|archive-date=28 June 2022|url-status=live|access-date=28 June 2022}} (JPL#73 Soln.date: 2022-Jun-07)</ref>

<ref name="Horizons2209">{{cite web|title=Horizons Batch for 1P/Halley (90000030) on 2209-Feb-03 and 2209-Apr-10|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]|type=Perihelion occurs when rdot flips from negative to positive|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272209-Feb-01%27&STOP_TIME=%272209-Apr-20%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719,20,23%27|archive-url=https://web.archive.org/web/20220630125454/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000030%27&START_TIME=%272209-Feb-01%27&STOP_TIME=%272209-Apr-20%27&STEP_SIZE=%273+hours%27&QUANTITIES=%2719%2C20%2C23%27|archive-date=30 June 2022|url-status=live|access-date=30 June 2022}} (JPL#73 Soln.date: 2022-Jun-07)</ref>

<ref name=":0">{{Cite journal|last=Lynn|first=W. T.|year=1909|title=Halley's Comet in 1835|journal=The Observatory|volume=32|pages=175–177|bibcode=1909Obs....32..175L}}</ref>

<ref name=":2">{{Cite journal|last=Smith|first=J. A.|year=1986|title=Halley's Comet: Canadian Observations and Reactions 1835–36 and 1910|journal=Journal of the Royal Astronomical Society of Canada|volume=80|issue=1|pages=1–15|bibcode=1986JRASC..80....1S}}</ref>

<ref name="Lamy2004">{{cite book|first1=Philippe L.|last1=Lamy|first2=Imre|last2=Toth|first3=Yanga R.|last3=Fernández|first4=Harold A.|last4=Weaver|chapter=The Sizes, Shapes, Albedos, and Colors of Cometary Nuclei|pages=223–264|bibcode=2004come.book..223L|chapter-url={{GBurl|AHF9ZraafV8C|p=223}}|editor1-last=Festou|editor1-first=M.|editor2-last=Keller|editor2-first=H. U.|editor3-last=Weaver|editor3-first=Harold A.|title=Comets II|date=2004|publisher=University of Arizona Press|isbn=978-0-8165-2450-1}}</ref>

<ref name="Brady1987">{{cite journal|title=Halley's Comet AD&nbsp;1986 to 2647&nbsp;BC|first=Joseph L.|last=Brady|publisher=Lawrence Livermore Laboratory, University of California|date=1982|bibcode=1982JBAA...92..209B|volume=92|page=209|journal=Journal of the British Astronomical Association}}</ref>

<ref name="yeo_p81">{{Cite journal|title=The History of Comet Halley|first1=Donald Keith|last1=Yeomans|first2=Jürgen|last2=Rahe|first3=Ruth S.|last3=Freitag|journal=Journal of the Royal Astronomical Society of Canada|volume=80|page=81|bibcode=1986JRASC..80...62Y|date=1986}}</ref>

<ref name="yeo">{{Cite journal|title=The History of Comet Halley|first1=Donald Keith|last1=Yeomans|first2=Jürgen|last2=Rahe|first3=Ruth S.|last3=Freitag|journal=Journal of the Royal Astronomical Society of Canada|volume=80|page=70|bibcode=1986JRASC..80...62Y|date=1986|quote=Figure 4. The minimum and maximum intervals are 74.42 years (1835-1910) and 79.25 years (451-530).}}</ref>

<ref name="Russell1988">{{Cite journal|title=The interaction of the solar wind with Comet Halley – Upwind and downwind|last=Russell|first=C. T.|journal= Quarterly Journal of the Royal Astronomical Society|volume=29|date=June 1988|pages=157–173|bibcode=1988QJRAS..29..157R|url=https://articles.adsabs.harvard.edu//full/1988QJRAS..29..157R/0000160.000.html}}</ref>

<ref name="hughes1987">{{Cite journal|first1=David W.|last1=Hughes|first2=P. H.|last2=Fowler|first3=B.|last3=Lovell|first4=D.|last4=Lynden-Bell|s2cid=123592786|display-authors=etal|title=The History of Halley's Comet [and Discussion]|journal=[[Philosophical Transactions of the Royal Society A]]|pages=349–367|jstor=37959|volume=323|number=1572|date=September 1987|doi= 10.1098/rsta.1987.0091|bibcode=1987RSPTA.323..349H}}</ref>

<ref name="Guardian_17Oct2024">{{Cite news|last=Ferguson|first=Donna|date=16 October 2024|title=X-ray evidence of Black maths scholar portrait reveals snubbed genius|url=https://www.theguardian.com/artanddesign/2024/oct/16/x-ray-evidence-black-maths-scholar-portrait-francis-williams-uncovers-genius|access-date=17 October 2024|work=The Guardian|issn=0261-3077}}</ref>

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*Reprinted in {{Cite book |editor=Grewing, M. |editor2=Praderie, F. |editor3=Reinhard, R. |title=Exploration of Halley's Comet |date=1988 |pages=807–823 |publisher=Springer |location=Berlin, Heidelberg |doi=10.1007/978-3-642-82971-0_138 |isbn=978-3-642-82973-4 }}
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<ref name="mass">{{Cite journal|title=The nucleus of comet Halley: Surface structure, mean density, gas and dust production|first=H.|last=Rickman|url=https://www.sciencedirect.com/science/article/abs/pii/027311778990241X|journal=Advances in Space Research|volume=9|issue=3|year=1989|pages=59–71|doi=10.1016/0273-1177(89)90241-X|bibcode=1989AdSpR...9c..59R|url-access=subscription}}</ref>

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<ref name="situ">{{Cite book|title=Comets II|chapter-url=https://www.researchgate.net/publication/241381179|editor-first1=Michel|editor-last1=Festou|editor-first2=Horst Uwe|editor-last2=Keller|editor-first3=Harold A.|editor-last3=Weaver|editor-link3=Hal A. Weaver|chapter=In Situ Observations of Cometary Nuclei|first1=Horst Uwe|last1=Keller|first2=Daniel|last2=Britt|first3=Bonnie J.|last3=Buratti|first4=Nicolas|last4=Thomas|pages=211–222|date=2005|isbn=978-0-8165-2450-1|publisher=University of Arizona Press|archive-url=https://web.archive.org/web/20240701001518/https://www.researchgate.net/profile/Daniel-Britt/publication/241381179_In_situ_observations_of_cometary_nuclei/links/02e7e53c6858cb4a68000000/In-situ-observations-of-cometary-nuclei.pdf|archive-date=1 July 2024|url-status=live}}</ref>

<ref name="graw">{{cite encyclopedia|doi=10.1036/1097-8542.305800|title=Halley's Comet|last1=Brandt|first1=John C.|date=February 2018|encyclopedia=AccessScience|publisher=McGraw Hill}}</ref>

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<ref name="Walker1985">{{Cite journal|last=Walker|first=C. B. F.|title=Archaeoastronomy: Halley's comet in Babylonia|journal=[[Nature (journal)|Nature]]|volume=314|issue=6012|pages=576–577|date=18 April 1985|doi=10.1038/314576b0|bibcode=1985Natur.314..576W}}</ref>

<ref name="kronk">{{Cite web|first=Gary W.|last=Kronk|author-link=Gary W. Kronk|title=1P/Halley|url=http://cometography.com/pcomets/001p.html|archive-url=https://web.archive.org/web/20171123064132/http://cometography.com/pcomets/001p.html|archive-date=23 November 2017|url-status=live|publisher=cometography.com|access-date=13 October 2008}}</ref>

<ref name="Chambers">{{cite book|title=The Story of the Comets|url=https://archive.org/details/b31349596|first=George F.|last=Chambers|publisher=The Clarenden Press|year=1909|page=[https://archive.org/details/b31349596/page/123 123]}}</ref>

<ref name="Schultheis">{{Cite book|title=The Battle of the Catalaunian Fields, 451 AD: Flavius Aetius, Attila the Hun, and the Transformation of Gaul|first=Evan Michael|last=Schultheis|year=2019|page=70|chapter=5|publisher=Pen & Sword Military|isbn=978-1-5267-4565-1|url=https://www.academia.edu/5405694}}</ref>

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<ref name="greatcomets">{{Cite web|title=Great Comets in History|first=Donald Keith|last=Yeomans|publisher=Jet Propulsion Laboratory|url=http://ssd.jpl.nasa.gov/?great_comets|date=1998|access-date=15 March 2007}}</ref>

<ref name="annals_of_ulster">{{Cite web|url=https://celt.ucc.ie/published/T100001A/text482.html|title=The Annals of Ulster AD&nbsp;431–1201|work=Corpus of Electronic Texts|publisher=University College Cork|access-date=25 March 2024}}</ref>

<ref name="annals_of_the_four_masters">{{Cite web|url=https://celt.ucc.ie/published/T100005B/index.html|title=The Annals of the Four Masters|work=Corpus of Electronic Texts|publisher=University College Cork|access-date=25 March 2024}}</ref>

<ref name="Olson1979">{{Cite journal|last=Olson|first=Roberta J. M.|author-link=Roberta Olson|title=Giotto's portrait of Halley's Comet|journal=[[Scientific American]]|volume=240|issue=5|year=1979|pages=160–171|doi=10.1038/scientificamerican0579-160|jstor=24965203|bibcode=1979SciAm.240e.160O}}</ref>

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<ref name="1985JHA">{{Cite journal|author=Broughton, P.|year=1985|title=The First Predicted Return of Comet Halley|journal=Journal for the History of Astronomy|volume=16|issue=2|pages=123–132|doi=10.1177/002182868501600203|bibcode=1985JHA....16..123B|s2cid=118670662}}</ref>

<ref name="Todd Saw Halley's Comet in 1835">{{Cite journal|bibcode=1910PA.....18..127T|title=Saw Halley's Comet in 1835|last1=Todd|first1=William G.|journal=Popular Astronomy|year=1910|volume=18|page=127}}</ref>

<ref name="post">{{Cite journal|title=A Postencounter view of comets|first=D. Asoka|last=Mendis|journal=Annual Review of Astronomy and Astrophysics|volume=26|issue=1|pages=11–49|date=1988|bibcode=1988ARA&A..26...11M|doi=10.1146/annurev.aa.26.090188.000303}}</ref>

<ref name="Ridpath">{{cite web|date=1985|title=Through the comet's tail|work=Revised extracts from "A Comet Called Halley" by Ian Ridpath, published by Cambridge University Press in 1985|first=Ian|last=Ridpath|author-link=Ian Ridpath|url=http://www.ianridpath.com/halley/halley12.html|access-date=19 June 2011}}</ref>

<ref name="pfizer">{{cite web|date=16 May 2011|title=This Week in Science History: Halley's Comet|publisher=pfizer: ThinkScience Now|first=Brian|last=Nunnally|url=https://science.pfizer.com/content/this-week-in-science-history-halleys-comet/|access-date=19 June 2011|archive-url=https://archive.today/20121217174930/https://science.pfizer.com/content/this-week-in-science-history-halleys-comet/|archive-date=17 December 2012}}</ref>

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<ref name="TwainMovie">{{cite magazine|last=McCracken|first=Harry|date=5 October 1986|page=108|title=One of the best animated films in recent years, a splendid job|url=https://archive.org/details/cinefantastique_1970-2002/Cinefantastique%20Vol%2016%20No%204-5%20Oct%20%281986%29/page/n107/mode/1up?view=theater|magazine=[[Cinefantastique]]|publisher=Fourth Castle Micromedia|access-date=7 July 2024|quote=At the film's core, though, is a plot twist devised by the filmmakers themselves; it's Mark Twain himself who captains the zeppelin, in a suicidal mission to meet Halley's comet head-on and assure the truth of his famous prediction that his life would end with the comet's return.}}</ref>

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<ref name="Jan24">{{cite news|title=Telescope Builders See Halley's Comet From Vermont Hilltop|newspaper=The New York Times|first=Malcolm W.|last=Browne|author-link=Malcolm Browne|url=https://query.nytimes.com/gst/fullpage.html?sec=health&res=9904E3DE163BF933A1575BC0A963948260|access-date=10 January 2008|date=20 August 1985}} (Horizons shows the nucleus @ APmag +20.5; the coma up to APmag +14.3)</ref>

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<ref name="Ridpath2015">{{cite web|date=1985|title=Saying Hallo to Halley|work=Revised extracts from "A Comet Called Halley" by Ian Ridpath, published by Cambridge University Press in 1985|first=Ian|last=Ridpath|author-link=Ian Ridpath|url=http://www.ianridpath.com/halley/halley3.html#hallo|access-date=8 May 2015}}</ref>

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<ref name="Hromakina2021">{{cite journal|journal=Astronomy and Astrophysics|volume=647|date=March 2021|number=A71|doi=10.1051/0004-6361/202039737|title=Small Solar System objects on highly inclined orbits|author=T. Hromakina, I. Belskaya, Yu. Krugly, V. Rumyantsev, O. Golubov, I. Kyrylenko, O. Ivanova. S. Velichko, I. Izvekova, A. Sergeyev, I. Slyusarev and I. Molotov|pages=A71|arxiv=2101.04541}}</ref>

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<ref name="Ravené1897">{{cite journal|url=https://adsabs.harvard.edu/full/1897Obs....20..203R|first=Gustave|last=Ravené|title=The Appearance of Halley's Comet in A.D.{{nbsp}}141|journal=[[The Observatory (journal)|The Observatory]]|volume=20|date=9 March 1897|location=[[Milan]]|pages=203–205|bibcode=1897Obs....20..203R|access-date=8 October 2024|quote=The comet observed by the Chinese in A.D.{{nbsp}}141 is in fact Halley's Comet}}</ref>

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}} <!-- end of reflist -->

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* {{Cite book|last=Lequeux|first=James|url=https://books.google.com/books?id=ikqGCgAAQBAJ&pg=PA180|title=François Arago: A 19th Century French Humanist and Pioneer in Astrophysics|date=2015|publisher=Springer|isbn=978-3-319-20723-0|language=en}}
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* {{cite book|last=Needham|first=Joseph|author-link=Joseph Needham|title=Science and Civilisation in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth|chapter-url=https://books.google.com/books?id=jfQ9E0u4pLAC&pg=PA430|date=1959|publisher=Cambridge University Press|pages=430–433|chapter=Comets, meteors, and meteorites|isbn=978-0-521-05801-8 }}
* {{Cite book|last=Rayner|first=John D.|author-link=John Rayner|title=A Jewish Understanding of the World|publisher=Berghahn Books|date=1998|isbn=1-57181-973-8|pages=108–111}}
* {{Cite book|last1=Sagan|first1=Carl|author-link1=Carl Sagan|first2=Ann|last2=Druyan|author-link2=Ann Druyan|title=Comet|publisher=[[Random House]]|date=1985|isbn=0-394-54908-2|url=https://archive.org/details/comet00saga}}
* {{cite book|last=Schmude|first=Richard M.|title=Comets and How to Observe Them|date=2010|publisher=Springer|isbn=978-1-4419-5790-0|page=3|url=https://books.google.com/books?id=WemDVdrPIIUC&pg=PA3}}
* {{Cite book|last1=Shayler|first1=David J.|last2=Burgess|first2=Colin|title=NASA's Scientist-Astronauts|publisher=Praxis|chapter=Ending of Eras|date=2007|chapter-url=https://books.google.com/books?id=TweEC3h633AC&pg=PA431|access-date=7 January 2009|isbn=978-0-387-21897-7}}
* {{Cite book|last=Siddiqi|first=Asif A.|url=https://www.nasa.gov/connect/ebooks/beyond_earth_detail.html|title=Beyond Earth: A Chronicle of Deep Space Exploration|publisher=NASA History Program Office|year=2018|isbn=978-1-62683-042-4|location=United States|pages=149–150}}
* {{cite book|last=Yeomans|first=Donald Keith|title=Comets: A Chronological History of Observation, Science, Myth, and Folklore|url=https://archive.org/details/cometschronologi0000yeom|url-access=registration|pages=260–261|date=1991|publisher=Wiley and Sons|isbn=0-471-61011-9}}

==External links==
{{Commons category|Comet Halley}}
* {{JPL Small Body|name=1P/Halley|id=1000036}}
* [https://books.google.de/books?id=bKAwAAAAYAAJ&pg=RA2-PA1 Synopsis of the Astronomy of Comets] (1706 reprint of Halley's 1705 paper)
* [https://web.archive.org/web/20110927022415/http://sse.jpl.nasa.gov/multimedia/display.cfm?IM_ID=11423 Image of Halley's Comet] by the ''Giotto'' spacecraft
* [http://spider.seds.org/spider/Comets/halley.html seds.org], links to images and further information about Halley's Comet
* [https://web.archive.org/web/20190520001326/http://digitalcollections.ucsc.edu/cdm/search/collection/p265101coll10/searchterm/Halley%27s%20Comet/order/title Photographs of 1910 approach] from the Lick Observatory Records Digital Archive
* [https://hdr-astrophotography.com/simulation-atlas-of-past-comets-antiquity-to-1699/ HDR Astrophotography: Simulations Atlas of Past Comets (Antiquity to 1699)] by Nicolas Lefaudeux
* [https://hdr-astrophotography.com/simulations-of-past-comets/ HDR Astrophotography: Simulations Atlas of Past Comets (1900 to 1999)] by Nicolas Lefaudeux

{{PeriodicComets Navigator|PageName=1P/Halley||2P/Encke}}
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{{DEFAULTSORT:Halley, 001P}}
[[Category:Halley's Comet|Halley's Comet]]
[[Category:Astronomical objects known since antiquity]]
[[Category:Comets visited by spacecraft]]
[[Category:Halley-type comets|001P]]
[[Category:Meteor shower progenitors|001P]]
[[Category:Near-Earth comets|001P]]
[[Category:Numbered comets|0001]]
[[Category:Periodic comets]]
[[Category:Star of Bethlehem]]
[[Category:Great comets]]
[[Category:Mark Twain]]
[[Category:1531 in science]]
[[Category:1607 in science]]
[[Category:1682 in science]]
[[Category:1759 in science]]
[[Category:1835 in science]]
[[Category:1910 in science]]
[[Category:1986 in science]]
[[Category:2061 in science]]