Halley's_Comet - Wikiparency

# Halley's Comet  **Microsim — three.js (Wikitube framework):** *Halley's Comet in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Halley&embed=1" data-title="Halley's Comet in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=Halley`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: set the speed to 10 years/s and watch Halley swing round the Sun inside the orbit of Venus, then climb for decades out past Neptune, moving against the planets the whole way; drag to an edge-on view to see its orbit tilted about 18° out of the planets' plane; then drag the year slider to 1835, 1910 and 1986 to catch it close to the Sun at three returns.* **Halley's Comet**, officially 1P/Halley, is a periodic [[Comet|comet]] that returns to the inner [[PORTAL_Solar_System|Solar System]] every 74–79 years and is the only short-period comet regularly bright enough to see with the unaided eye from [[Earth]].[^brady1982][^delehanty] It last passed the [[Sun]] in 1986 and will next reach perihelion on 28 July 2061.[^horizons2061] Its returns have been recorded since at least 240 BC, but it was Edmond Halley who showed in 1705 that sightings 75–76 years apart were one comet, and predicted its return; the comet was named for him when it came back in 1759.[^kronk1999][^hughes1987] Its [[Orbit|orbit]] is long, eccentric and retrograde, carrying it from just inside the orbit of [[Venus]] out beyond [[Neptune]].[^jpl-sbdb] In March 1986 it became the first comet whose nucleus was seen close up, by the Soviet Vega 1 and 2 and the European Giotto spacecraft. They found a dark, irregular nucleus about 15 km long, mostly covered in dust, with jets of gas escaping from a small active fraction of its surface.[^keller2005][^mendis1988] The explorer at the top of this page follows Halley on its orbit about the Sun among the planets, computed as a two-body ellipse from its orbital elements of 1968, so its position at other epochs is approximate. ## Pronunciation The name is usually said to rhyme with "valley", and sometimes with "daily".[^merriam][^ridpath-hallo] The astronomer's own name is less certain. In his lifetime it was written Hailey, Haley, Hayley, Halley, Haly, Hawley and Hawly, which leaves its contemporary sound open, and one of his biographers, Colin Ronan, favoured a version rhyming with "crawly".[^ridpath-hallo][^nyt1985] Modern holders of the surname mostly use the "valley" form, which has become the common one for the comet.[^nyt1985] The formal name is less ambiguous. In the comet designation system the prefix P/ marks a periodic comet, and the number 1 records that this was the first comet recognised as periodic; 1P/Halley therefore heads the numbered list of periodic comets.[^icq-names][^mpc-1p] Each return also carries its own designation, so that the 1986 apparition was catalogued as 1P/1982 U1, from the half-month of its recovery in October 1982, and under the older system as 1986 III, the third comet to pass perihelion in 1986, and 1982i, the ninth found in 1982.[^icq-names][^marsden1996] The name "Halley's Comet" itself was first applied by the French astronomer Nicolas-Louis de Lacaille in 1759, after the predicted return.[^hughes1987] ## Computation of orbit Halley was the first comet recognised as periodic, and its recognition depended on new physics. Aristotle's view that comets were disturbances in the upper air had been undermined by Tycho Brahe in 1577, whose parallax measurements placed a comet beyond the [[Moon]], but many astronomers still assumed comets moved on straight lines.[^lancaster1985] [[Isaac_Newton|Isaac Newton]]'s *Principia* of 1687 supplied [[Newton's_law_of_universal_gravitation|universal gravitation]], under which a body falling around the Sun must follow a conic section, though Newton's own treatment of comets remained incomplete.[^hughes1988] Halley, Newton's friend and publisher, applied the method in his *Synopsis of the Astronomy of Comets* of 1705. From 24 well-observed comets he found that those of 1531, seen by Petrus Apianus, 1607, seen by [[Johannes_Kepler|Johannes Kepler]], and 1682, which Halley saw himself, had nearly the same orbital elements.[^lancaster1985][^halley1705] He concluded they were one comet with a period of about 76 years, the differences between intervals arising from the pull of [[Jupiter]] and [[Saturn]], and predicted its return for 1758. He died in 1742.[^lancaster1985] The comet was recovered on 25 December 1758 by Johann Georg Palitzsch, a German farmer and amateur astronomer.[^lancaster1985] Alexis Clairaut, Jérôme Lalande and Nicole-Reine Lepaute had computed that the planets would delay it by 618 days, and predicted perihelion for 13 April 1759; it came on 13 March, within their stated margin of a month.[^lancaster1985][^broughton1985] The return was the first demonstration that bodies other than planets orbit the Sun, and one of the earliest decisive tests of Newtonian mechanics.[^hughes1987] In Jamaica, the mathematician Francis Williams independently recorded the return; a portrait he commissioned shows him with Newton's *Principia* open at the section on comets, and X-ray imaging in 2024 showed the star field in which the comet then stood.[^dabhoiwala2024][^ferguson2024] Calculating the orbit backward is harder. Numerical integrations from 17th- and 18th-century observations lose accuracy before 837, when the comet passed very close to Earth, and ancient Chinese records have been used to constrain earlier returns.[^stephenson1984] ## Orbit and origin Halley's period has ranged from about 74 to 80 years since 240 BC.[^yeomans1986] The orbit has a semi-major axis of 17.9 [[Astronomical_unit|AU]] and an eccentricity of 0.968, with perihelion at 0.58 AU, between the orbits of [[Mercury_(planet)|Mercury]] and Venus, and aphelion at 35 AU, beyond Neptune.[^jpl-sbdb] By [[Kepler's_laws_of_planetary_motion|Kepler's third law]], 17.9^1.5 ≈ 76 years (derived). Its inclination of 162° means that it is tilted 18° from the [[Ecliptic|ecliptic]] but travels backwards, opposite to the planets.[^jpl-sbdb][^nasa-basics] At perihelion it moves at about 55 km/s, and at aphelion, which it reached on 9 December 2023, at only 0.91 km/s.[^horizons2023] The perihelion speed follows from the vis-viva equation (derived). Because the retrograde orbit meets Earth nearly head-on, it passed Earth in 1910 at a relative speed of 70.56 km/s.[^jpl-sbdb] Its orbit comes close to Earth's in two places, and its debris produces two [[Meteor_shower|meteor showers]], the Eta Aquariids in May and the Orionids in October.[^jpl-streams] Halley is a periodic comet, with a period under 200 years, but an unusual one: most periodic comets have inclinations near 10° and periods near 6.5 years.[^hughes1987] Comets like it, with periods of 20–200 years and any inclination, are called Halley-type comets; about 105 were known in 2024, against more than 800 Jupiter-family comets.[^morbidelli2005][^jewitt2002][^jpl-sbdbq] Halley-type comets are thought to be former long-period comets from the [[Oort_cloud|Oort cloud]] captured by the giant planets, although the [[Scattered_disc|scattered disc]] has also been proposed as a source; the discovery in 2008 of a [[Trans-Neptunian_object|trans-Neptunian object]] on a retrograde orbit like Halley's supported that idea.[^jewitt2002][^gladman2009][^levison2006] Halley has probably been in its present orbit for 16,000–200,000 years.[^olsson1987] Jets of escaping gas push it slightly off a purely gravitational path, delaying perihelion by about four days on average.[^yeomans1991] Boris Chirikov and Vitold Vecheslavov showed in 1989, from 46 apparitions, that its motion is chaotic over long times, with an expected dynamical lifetime of about 10 million years.[^chirikov1989] David Hughes estimated in 1985 that the nucleus has lost 80–90% of its mass over the last 2,000–3,000 orbits and may vanish after about 2,300 more; more recent work suggests it will evaporate or split within a few tens of thousands of years, or be ejected within a few hundred thousand.[^hughes1985][^jewitt2002] ## Structure and composition The nucleus is a conglomerate of ices and dust. Near the Sun its volatile ices, chiefly [[Water|water]] with carbon monoxide and carbon dioxide, sublimate and form a coma extending as far as 230,000 km from the nucleus.[^brandt2018][^altwegg1993] Gas in the coma absorbs and re-emits sunlight while dust scatters it, and ionised gas is swept by the [[Solar_wind|solar wind]] into a tail that can exceed 100 million kilometres; changes in the wind can snap the tail off entirely in a disconnection event.[^brandt2018][^brandt1987] The nucleus is small for so bright a comet: about 15 km long and 8 km wide, with an effective diameter of about 11 km, and shaped like a peanut or potato.[^keller1987][^lamy2004] Its mass is about 2.2 × 10¹⁴ kg and its mean [[Density|density]] about 0.55 g/cm³, low enough to suggest a loosely bound rubble pile.[^rickman1989][^keller2005][^sagdeev1988] Its rotation is complex, with periods of 52 hours and about 7.4 days both found in the data.[^keller2005] The flyby images show hills, ridges, depressions and at least one crater.[^keller2005] The day side is far more active than the night side. Gas released was about 80% water vapour, 17% carbon monoxide and 3–4% carbon dioxide, with traces of hydrocarbons, though later analyses give nearer 10% carbon monoxide.[^woods1986][^chyba1987][^esa-giotto] The dust is a mixture of silicates and CHON particles, rich in [[Carbon|carbon]], [[Hydrogen|hydrogen]], [[Oxygen|oxygen]] and [[Nitrogen|nitrogen]], down to grains of about 0.001 micrometres.[^brandt2018][^mendis1988] The ratio of deuterium to hydrogen in its water is higher than in Earth's oceans, which argues against Halley-type comets as the main source of Earth's water.[^brandt2018] Giotto confirmed Whipple's icy-nucleus model in broad outline but changed its details. Halley's albedo is about 0.04, as dark as coal, rather than the 0.17 that had been expected.[^weaver1997][^belton1982] Vega 1 measured surface temperatures of 300–400 K, well above those of sublimating ice, which implied that only about 10% of the surface was active and the rest was covered by a dark, insulating dust layer. Halley is therefore closer to an icy dirtball than a dirty snowball.[^mendis1988][^keller2005] ## History About one in eight comet sightings in historical records is of Halley, because it is intrinsically bright and returns often.[^hughes1987] ### Before 1066 The first certain record is from 240 BC, in the Chinese *Records of the Grand Historian*.[^kronk1999] Babylonian tablets in the British Museum, identified in 1984, record the returns of 164 and 87 BC.[^stephenson1985][^walker1985] Vahe Gurzadyan and Ruben Vardanyan have suggested that a star with a curved tail on coins of the Armenian king Tigranes the Great depicts the 87 BC comet.[^gurzadyan2004] The apparition of 12 BC was followed by Chinese astronomers for two months and passed 0.16 AU from Earth.[^kronk-1p][^yeomans1998] A Talmudic reference to "a star which arises once in seventy years" and the comet that Josephus says hung over Jerusalem before the war of 66–70 AD may both refer to the 66 AD return.[^sefaria][^josephus] The 451 apparition was linked to the defeat of Attila the Hun.[^schultheis2019] In 837 the comet passed only about 0.03 AU from Earth, its closest known approach, with a tail stretching perhaps 60° across the sky.[^horizons837][^yeomans1998] ### 1066 In 1066 the comet appeared in April, months before Harold II was killed at the Battle of Hastings, and was taken as an omen of the Norman conquest. It is shown on the Bayeux Tapestry. It passed 0.10 AU from Earth.[^yeomans1998] Irish annals describe a star whose light rivalled the Moon's, visible for four nights.[^four-masters] ### 1145–1378 The 1145 return is depicted in the Eadwine Psalter.[^olson1979] In 1222 the comet was reported visible in daylight in Korea.[^choi2017] The 1301 return inspired Giotto di Bondone's Star of Bethlehem in his *Adoration of the Magi* in Padua, a realistic comet with coma and tail, and led ESA to name its probe after the painter.[^olson1979][^olson1986] The 1378 return is recorded in Milanese and East Asian sources.[^kronk1999] ### 1456 In 1456, as Ottoman forces besieged Belgrade, Pope Callixtus III ordered prayers for the city; the later story that he excommunicated the comet is a fabrication.[^emerson][^botley1971] The comet was also recorded in Kashmir by the poet Śrīvara and in a copper-plate inscription of the Vijayanagara period.[^slaje2012][^gattimi2025] ### 1531–1759 Petrus Apianus observed the 1531 return and showed that a comet's tail points away from the Sun.[^barker2008] Halley's study of the 1531, 1607 and 1682 comets, drawing on John Flamsteed's observations, led to the prediction described above; the comet duly returned in December 1758.[^broughton1985] ### 1835 The 1835 return was widely observed, by Friedrich Struve at Dorpat, John Herschel at the Cape of Good Hope and astronomers at Yale.[^lynn1909][^smith1986] Friedrich Bessel sketched streams of vapour from the nucleus and proposed that their reaction could shift a comet's orbit.[^sagan1985] Mark Twain was born two weeks after that perihelion.[^paine1912] ### 1910 The 1910 return, with perihelion on 20 April and closest approach of 0.15 AU, was the first to be photographed and studied spectroscopically.[^yeomans1998][^mendis1988] Earth passed through the tail in May. The discovery of cyanogen in the tail led to fears of poisoning, and some people bought gas masks and "anti-comet pills" despite reassurances from astronomers.[^nyt1910][^strauss2009] Mark Twain, who had predicted that he would "go out with it", died on 21 April, the day after perihelion.[^paine1912] ### 1986 The 1986 return was the least favourable on record, with the comet on the far side of the Sun from Earth at perihelion on 9 February and no closer than 0.42 AU.[^broughton1979][^jsc1985] David Jewitt and G. Edward Danielson recovered it on 16 October 1982 with the 5.1 m Hale Telescope.[^esa-recovered] The Halley Armada studied it at close range: Vega 1 and 2 flew past on 6 and 9 March, Giotto passed closest on 14 March, and the Japanese Suisei and Sakigake observed from farther away.[^keller2005][^jaxa-suisei] The International Cometary Explorer observed it from about 40 million km on 28 March 1986, and the loss of the space shuttle Challenger in January 1986 ended a planned ultraviolet study from orbit.[^nasa-ice][^nasa-51l] ### After 1986 On 12 February 1991, at 14.3 AU from the Sun, Halley unexpectedly brightened in an outburst lasting months, rare for a comet so far out; the likely cause was the crystallisation of amorphous water ice.[^west1991][^prialnik1992] In 2003 the Very Large Telescope imaged it at magnitude 28.2 at 28 AU, the most distant comet then imaged.[^eso2003] ### 2061 The next perihelion falls on 28 July 2061, with the comet on the same side of the Sun as Earth, closest to Earth a day later, and expected to reach magnitude −0.3.[^horizons2061][^odenwald] It will pass 0.0543 AU from Venus on 20 August 2061.[^jpl-sbdb] ### 2134 Perihelion is expected on 27 March 2134, and on 7 May 2134 the comet will pass 0.092 AU from Earth, reaching an estimated magnitude of −2.0.[^horizons2134][^odenwald] ### List of apparitions Halley's orbit allowed its earlier returns to be identified in historical records. Dates before 1582 are Julian; those before 837 are uncertain by a few days.[^sitarski1988] Selected returns: | Year | Perihelion | Closest to Earth | Note | |---|---|---|---| | 240 BC | 30 March | — | first certain record[^kronk1999] | | 12 BC | 5 October | 0.16 AU | followed by Chinese astronomers[^yeomans1998] | | 837 | 28 February | 0.03 AU | closest known approach[^horizons837] | | 1066 | 23 March | 0.10 AU | Bayeux Tapestry[^yeomans1998] | | 1759 | 13 March | — | first predicted return[^lancaster1985] | | 1910 | 20 April | 0.15 AU | first photographed[^yeomans1998] | | 1986 | 9 February | 0.42 AU | first spacecraft visits[^jsc1985] | | 2061 | 28 July | 0.48 AU | next return[^horizons2061] | ## See also - [[Comet]] · [[Meteor_shower]] · [[Oort_cloud]] · [[Scattered_disc]] - List of Halley-type comets ## Notes Derived values: with a = 17.9 AU and q = 0.575 AU from the JPL Small-Body Database, the vis-viva equation v² = GM☉(2/r − 1/a) gives about 55 km/s at perihelion, and Kepler's third law gives P = a^1.5 ≈ 76 years. The explorer's orbit is a two-body ellipse from the 1968 elements; it ignores the planetary perturbations that make the real period vary between 74 and 80 years. ## References [^brady1982]: Brady, J. L. (1982). "Halley's Comet: AD 1986 to 2647 BC". *Journal of the British Astronomical Association* 92: 209. Bibcode 1982JBAA...92..209B. [^delehanty]: Delehanty, M. "Comets, awesome celestial objects". *AstronomyToday*. http://www.astronomytoday.com/astronomy/comets.html [^horizons2061]: JPL Horizons. "Horizons batch for 1P/Halley on 2061-Jul-28". https://ssd.jpl.nasa.gov/horizons/ [^kronk1999]: Kronk, G. W. (1999). *Cometography: A Catalog of Comets*, vol. 1. Cambridge University Press, pp. 6, 253–255. [^hughes1987]: Hughes, D. W. (1987). "The history of Halley's Comet". *Philosophical Transactions of the Royal Society A* 323: 349–367. https://doi.org/10.1098/rsta.1987.0091 [^jpl-sbdb]: JPL Solar System Dynamics. 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"On the nongravitational motion of comet P/Halley". *Acta Astronomica* 38: 253–268. Bibcode 1988AcA....38..253S. ## Bibliography - Lancaster-Brown, P. (1985). *Halley & His Comet*. Blandford Press. - Sagan, C.; Druyan, A. (1985). *Comet*. Random House. - Kronk, G. W. (1999). *Cometography: A Catalog of Comets*, vol. 1. Cambridge University Press. - Yeomans, D. K. (1991). *Comets: A Chronological History of Observation, Science, Myth, and Folklore*. Wiley. ## External links - NASA Science: 1P/Halley. https://science.nasa.gov/solar-system/comets/1p-halley/ - JPL Small-Body Database: 1P/Halley. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=1P - ESA: Giotto mission. https://www.esa.int/Science_Exploration/Space_Science/Giotto_overview - Ian Ridpath, *A Brief History of Halley's Comet*. http://www.ianridpath.com/halley/ ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Halley's_Comet) : [Wikitube](https://en.wikitube.io/wiki/Halley's_Comet) · pinned revision [1375206184](https://en.wikipedia.org/w/index.php?oldid=1375206184) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-084 · explorer state `?obj=Halley`.*