(Redirected from Comet Halley)
'Halley's Comet', officially designated '1P/Halley' and also referred to as 'Comet Halley' after
Edmond Halley, is a
comet that can be seen every 75–76 years. It is the most famous of all
periodic comets. Although in every century many long-period comets appear brighter and more spectacular, Halley is the only short-period comet that is clearly visible to the naked eye, and thus, the only naked-eye comet certain to return within a human lifetime.
[1] Halley's Comet last appeared in the inner
Solar System in 1986, and will next appear in mid
2061.
The most standard pronunciation of "Halley" is [] (
IPA), to rhyme with "valley". The once-standard alternate pronunciation [] (to rhyme with "Bailey") led to
rock and roll singer Bill Haley naming his band
Bill Haley and the Comets. Edmond Halley himself probably pronounced his name [], with the "hall-" rhyming with "call" or "small".
[2]
Edmond Halley's study
Halley's Comet was the first comet to be recognized as periodic. Perceiving that the observed characteristics of the comet of 1682 were nearly the same as those of two comets which had appeared in 1531 (observed by
Petrus Apianus) and 1607 (observed by
Johannes Kepler in
Prague), Halley concluded that all three comets were in fact the same object returning every 76 years (a period that has since been amended to every 75–76 years). After a rough estimate of the perturbations the comet would sustain from the attraction of the planets, he predicted its return for 1757. 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, and did not pass through its
perihelion until March 1759; the attraction of
Jupiter and
Saturn having caused a retardation of 618 days, as was computed by a team of three
French mathematicians,
Alexis Clairault,
Joseph Lalande, and
Nicole-Reine Lepaute, previous to its return. Halley did not live to see the comet's return, having died in 1742.
Notable appearances
Halley's calculations enabled the comet's earlier appearances to be found in the historical record.
Early appearances
A
Babylonian tablet recording the appearance of Halley's comet in 164 BC.
The comet's appearance in 1066 was recorded on the
Bayeux Tapestry. ''ISTI MIRANT STELLA'' literally means "These ones are looking at the star". ''
National Geographic'' translated it in a 1966 article about the tapestry as "These men wonder at the star."
★ 240 BC and earlier: Historical records show that Chinese astronomers observed the comet's appearance in 240 BC and possibly as early as 2467 BC. Habitual observations and calculations of appearances after 240 BC are recorded by Chinese, Babylonian, Persian, and other Mesopotamian astronomers.
★ 87 BC: According to V.G. Gurzadyan and R. Vardanyan, the "Symbol on
Tigranes the Great's crown that features a star with a curved tail may represent the passage of Halley's comet in 87 BC. Tigranes could have seen Halley's comet when it passed closest to the Sun on Aug. 6 in 87 BC according to the researchers, who said the comet would have been a 'most recordable event' — heralding the New Era of the brilliant King of Kings.
[3]
★ 12 BC: Some
theologians have suggested that the comet's appearance in 12 BC might explain the Biblical story of the
Star of Bethlehem.
[4]
★ 66 AD: In the
Talmud, it is mentioned that "There is a star which appears once in seventy years that makes the captains of the ships err".
[5] Since this quote is attributed to the Rabbi
Yehoshua ben Hananiah, if it is indeed a reference to Halley's Comet, it probably refers to the AD 66 perihelion, which was the only one to occur during his lifetime.
[6]
★ 837: In this year, it is calculated that Comet Halley may have passed as close as 0.03
AU (3.2 million miles) from
Earth, by far its closest approach. Its tail may have stretched 90
degrees across the sky.
[7]
★ 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. Thus it was a bad omen for Harold, but a good omen for
William the Conqueror. It is shown on the
Bayeux Tapestry, and the accounts which have been preserved represent it as having then appeared to be four times the size of
Venus, and to have shone with a light equal to a quarter of that of the
Moon. This appearance of the comet is also noted in the
Anglo-Saxon Chronicle. Having first seen it as a young boy in 989,
Eilmer of Malmesbury declared prophetically in
1066: "You've come, have you?…You've c—ome, you source of tears to many mothers, you evil. I hate you! 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. I hate you!"
[8].
Chaco Native Americans in New Mexico recorded this 1066 comet in their petroglyphs.
[9]
★ 1301: The artist
Giotto di Bondone could have observed the comet and his depiction of the Star of Bethlehem in the
Nativity in the
Arena Chapel cycle completed in 1305 is a candidate for an early depiction.
★ 1456: The comet passed very close to the Earth; its tail extended over 60° of the heavens and took the form of a sabre. According to one story, first appearing in a posthumous biography in 1475 and later embellished and popularized by
Pierre-Simon Laplace,
Pope Callixtus III excommunicated the 1456 apparition of the comet, believing it to be an ill omen for the Christian defenders of
Belgrade, who were at that time being besieged by the armies of the
Ottoman Empire. However, no known primary source supports the authenticity of this account.
Recent history
The most recent appearances have been in 1835, 1910, and 1986. Halley will next return in 2061 or 2062.
1835
American satirist and writer
Mark Twain was born on
November 30,
1835, exactly two weeks after the comet's
perihelion. In his biography, he said, "I came in with Halley's comet in 1835. It's coming again next year (1910), and I expect to go out with it. The Almighty has said no doubt, 'Now here are these two unaccountable freaks; they came in together, they must go out together.' " Twain died on
April 21,
1910, the day following the comet's subsequent perihelion.
[10][11] The 1985 fantasy film ''
The Adventures of Mark Twain'' is inspired by this.
1910
The April 1910 approach was notable for several reasons: it was the first approach of which photographs exist, and the comet made a relatively close approach, making it a spectacular sight. Indeed, on
May 18, the comet
transited the Sun's disk, and the Earth actually passed through its tail. At the time, the comet's tail was thought to contain poisonous
cyanogen and gas. The popular media picked up this fact and, despite the pleas of astronomers, wove sensational tales of mass cyanide poisoning engulfing the planet. In reality, the gas is so diffuse that the world suffered no ill-effects from the passage through the tail.
Many people who claim to remember seeing the 1910 apparition are in fact remembering a different comet, the
Great Daylight Comet of 1910, which surpassed Halley in brilliance and was actually visible in broad daylight for a short time about four months before Halley made its appearance.
1986
Comet Halley in 1986
The 1986 approach was the least favourable for Earth observers of all recorded passages of the comet throughout history: the comet did not achieve the spectacular brightness of some previous approaches, and with increased
light pollution from urbanization, many people never saw the comet at all. Further, the comet appeared brightest when it was almost invisible from the northern hemisphere in March and April, prompting many amateur astronomers to travel to the southern hemisphere for a glimpse of the interloper. However, the development of space travel allowed scientists the opportunity to study a comet at close quarters, and several probes were launched to do so. The
Soviet Vega 1 started returning images of Halley on
1986 March 4, and the first ever of its nucleus, and made its flyby on March 6, followed by
Vega 2 making its flyby on March 9. On March 14, the
Giotto space probe, launched by the
European Space Agency, made a closest pass of the comet's nucleus. There were also two
Japanese probes,
Suisei and
Sakigake. The probes were unofficially known as the
Halley Armada.
The first person who visually observed Comet Halley on its 1986 return was famous amateur astronomer Stephen James O'Meara in 1985 January 23-24. O'Meara used 24" telescope and the Comet had magnitude 19.6 when he detected it. As for the naked eye observing, it was Stephen Edberg (then serving as the Coordinator for Amateur Observations at
NASA's Jet Propulsion Laboratory (
JPL)) and Charles Morris who were the first to observe Comet Halley with the naked eye in its 1986 apparition.
Based on data, retrieved by
Astron, the largest
ultraviolet space telescope of the time, during its Halley's Comet observations in December, 1985, a group of
Soviet scientists developed a model of the comet's
coma.
[12] The comet was also observed from space by the
International Cometary Explorer. Originally International Sun-Earth Explorer 3 the probe was renamed and freed from its L1
Lagrangian point location in Earth's orbit to intercept comets
21P/Giacobini-Zinner and Halley.
Two
Space Shuttle missions — the ill-fated
STS-51-L and
STS-61-E — were scheduled to observe Comet Halley from
low Earth orbit. 61-E, which would have been flown by ''
Challenger'' in March 1986, would have carried the
ASTRO-1 platform to study the comet, among other things. The ''Challenger'' disaster thwarted all such plans. ASTRO-1 would not fly until late 1990 on
STS-35.
[13]
Origin
Comets are believed to have two separate points of origin in the Solar System; the
Kuiper belt, a flat disc of icy debris at roughly fifty
AU from the Sun (Just beyond Pluto), and the
Oort cloud, a sphere of cometary bodies which has its inner edge at 50,000 AU. Short period comets (those with orbits lasting 200 years or less) are generally accepted to have emerged from the Kuiper belt, while
long period comets, such as
Hale-Bopp, whose orbits last for thousands of years, are believed to originate in the Oort cloud. Halley is unusual in that while it is a short period comet, its ultimate origin lies in the Oort cloud, not the Kuiper belt. Its orbit is such that it is believed to have been originally a long period comet but to have been captured by the gravity of the giant planets and sent into the inner Solar System. Halley is grouped with other comets that share this orbit into the Halley family comets.
[14]
Orbit
Halley's orbit is highly
elliptical, and focused on the Sun. Its
perihelion, its closest distance to the Sun, is just 0.6 AU (between the orbits of
Mercury and
Venus), while its
aphelion, or farthest distance from the Sun, is 35 AU, or roughly the distance of
Pluto. Unusually for an object in the
Solar System, Halley's orbit is
retrograde; it orbits the Sun in the opposite direction to the planets, or clockwise from above the
Sun's north pole. Its orbit is highly inclined (18°) to the
ecliptic, with much of it lying below the orbits of the planets (assuming Earth's north pole is "up").
[15][16]
Structure and composition
The ''Giotto'' mission gave planetary scientists their first view of Halley's surface and structure. Although its
coma extends for millions of kilometres into space, Halley's
nucleus is relatively small (barely 15 kilometres long, 8 kilometres wide and 8 kilometres thick) and roughly
peanut-shaped. Its mass is extremely low; roughly 2.2×10
14 kg.
[17]
Its average density is about 0.6 g/cm³, indicating that it is very loosely constructed.
[18] Its
albedo is about 4 percent, meaning that only 4 percent of the sunlight hitting it is reflected; about what one would expect for coal. Thus, despite appearing brilliant white to observers on Earth, Halley's comet is in fact pitch black. As it approaches the inner Solar System, the Sun warms it, causing its surface to
sublimate (change directly from a solid to a gas), and jets of volatile material to burst from its black surface. The nucleus rotates every 52 hours, and its day side is far more active than its night side. The gases ejected from the nucleus are 80 percent water vapour, 17 percent
carbon monoxide and 3–4 percent
carbon dioxide[19] with traces of hydrocarbons.
[20]
The nucleus is covered with a layer of dust which retains heat. Each large dust grain is thought to consist of many tiny particles with spaces in between. Some of these spaces are filled with ice, and others are empty. When Halley's comet is closest to the Sun, temperatures can rise to about 77 °C. Near the Sun, several tons of gas and dust are emitted each second in the jets. Halley has several shallow craters which are about 1 km in diameter.
Meteor showers
Because its orbit comes close to Earth's orbit in two places, Comet Halley is the parent body of two
meteor showers: the
Eta Aquarids in early May, and the
Orionids in late October.
[21] The Eta Aquarids show orbital similarites approaching Earth as they do of Mars and so a meteor shower at Mars is anticipated there as well
[22] but this time appearing to come from Lambda Gemini.
Designation
This table sets out the
astronomical designation for various
apparitions of Halley's Comet. For example, "(1P/1982 U1, 1986 III, 1982i" indicates that for the perihelion in
1986, Halley's Comet was the first period comet known (designated 1P) and this apparition was the first seen in "half-month" U (the first half of November) in 1982 (giving 1P/1982 U1); it was the third comet past perihelion in 1986 (1986 III); and it was the ninth comet spotted in 1982 (
provisional designation 1982i). The perihelion dates of each apparition are shown.
[23] that the perihelion dates farther from the present are approximate, mainly because of uncertainties in the modeling of non-gravitational effects.''
''Note that perihelion dates 1607 and later are in the
Gregorian calendar, whilst perihelion dates of 1531 and earlier are in the
Julian calendar.
[24]
External links
★
cometography.com
★
seds.org
★
JPL Orbit Simulation
★
Donald Yeomans, "Great Comets in History"
★
Vega 2 Images of Comet Halley
References
★ Halleio, Edmundo, ''Astronomiæ Cometicæ Synopsis, Autore Edmundo Halleio apud Oxonienses. Geometriæ Professore Saviliano, & Reg Soc. S.'', Philosophical Transactions, Vol. 24, No. 297, pp. 1882–1899
★ Hughes, D. W., ''The History of Halley's Comet'', Philosophical Transactions of the Royal Society of London, Series A, Vol. 323, No. 1572 (Sept. 30, 1987), pp. 349–367.
Footnotes
1. Comets, awesome celestial objects
2. Huygens, Halley & Harrison — Anniversaries 2006 Flamsteed Astronomy Society
3. Halley's comet of 87 BC on the coins of Armenian king Tigranes? Gurzadyan, V. G. and Vardanyan, R.
4. What's up with the star of Bethlehem? Cecil Adams
5. The Talmud: Harioth Chapter III
6. Astronomy in Israel:
From Og's Circle to the Wise Observatory Yuval Ne'eman
7. Great Comets in History
8. Deeds of the English Kings, William of Malmesbury, , , , ,
9. Chaco Canyon mystery tour
10. Directory of Mark Twain's maxims, quotations, and various opinions:
11. The New York Times: 1867-1970
12. A model for the coma of Comet Halley, based on the Astron ultraviolet spectrophotometry
13. Columbia
14. FROM KUIPER BELT OBJECT TO COMETARY NUCLEUS: THE MISSING ULTRARED MATTER DAVID C. JEWITT
15. Comet Halley Bill Arnett
16. OAA computing sectioncircular Syuichi Nakano
17. Halley, comet's mass loss and age G. Cevolani, G. Bortolotti and A. Hajduk
18. Is the nucleus of Comet Halley a low density body? RZ Sagdeev; PE Elyasberg; VI Moroz.
19. Rocket ultraviolet spectroscopy of comet Halley and abundance of carbon monoxide and carbon TN Woods; PD Feldman; KF Dymond; DJ Sahnow
20. Infrared emission by organic grains in the coma of comet Halley Christopher Chyba & Carl Sagan
21. Meteor Streams
22. Meteor Showers And Their Parent Bodies
23. 1P/Halley
24. Halley's Comet" AD 1986 to 2647 BC Joseph L. Brady
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