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Halley's Comet

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   CAPTION: 1P/Halley

   Comet
   ( List of comets)
   Comet Halley image taken by ESA's Giotto mission. Several bright jets
   of gas and dust are visible.
   Comet Halley as taken with the Halley Multicolor Camera on the ESA
   Giotto mission. The nucleus is sunlit from the left, and several bright
   jets of gas and dust are visible.
   Discovery
   Discoverer prehistoric;
   Named after Edmond Halley
   Discovery date 1758 (first predicted perihelion)
   Alternate
   designations Halley's Comet, 1P (see perihelia)
   Orbital elements ^A

                    Epoch 2449400.5 ( February 17, 1994)

   Eccentricity (e) 0.967
   Semi-major axis (a) 17.8 AU
   Perihelion (q) 0.586 AU
   Aphelion (Q) 35.1 AU
   Orbital period (P) 75.3 a
   Inclination (i) 162.3°
   Last perihelion date February 9, 1986
   Next est. perihelion date July 28, 2061

   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 visible to
   the naked eye, and thus, the only naked-eye comet certain to return
   within a human lifetime. Its many appearances over the centuries have
   had a notable effect on human history, despite the fact that they were
   not recognized as the same object until the 17th century. 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" — and the pronunciation
   that the astronomer himself probably used — is [hæli] ( IPA), to rhyme
   with "valley". The once-standard alternate pronunciation [heɪli] (to
   rhyme with "Bailey") led to rock and roll singer Bill Haley naming his
   band Bill Haley and the Comets.

Edmond Halley's study

   Halley's Comet was the first to be recognized as periodic. Having
   perceived 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 BCE.
   Enlarge
   A Babylonian tablet recording the appearance of Halley's comet in
   164 BCE.
   The comet's appearance in 1066 was recorded on the Bayeux Tapestry.
   ISTI MIRANT STELLA means "These ones are wondering at the star".
   Enlarge
   The comet's appearance in 1066 was recorded on the Bayeux Tapestry.
   ISTI MIRANT STELLA means "These ones are wondering at the star".
     * 240 BCE and earlier: Historical records show that Chinese
       astronomers observed the comet's appearance in 240 BCE and possibly
       as early as 2467 BCE. Habitual observations and calculations of
       appearances after 240 BC are recorded by Chinese, Japanese,
       Babylonian, Persian, and other mesopotamian astronomers.
     * 12 BCE: Some theologians have suggested that the comet's appearance
       in 12 BC might explain the Biblical story of the Star of Bethlehem.
     * 66 CE: 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" ( Horioth, chap. III). It probably refers to the AD 66
       perihelion.
     * 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.
     * 1066: The comet was seen in England and thought to be a bad omen:
       later that year Harold II of England died at the Battle of
       Hastings. 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 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" ( William of Malmesbury, Deeds of the
       English Kings, Ch. 225, ISBN 0-19-820678-X). Chaco Native Americans
       in New Mexico recorded this 1066 comet in their petriglyphs.
     * 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.

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. 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 18th, 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.

   Another person whose life coincided with arrivals of Halley's comet was
   French author Jean Genet; born in 1910, he died in 1986.

1986

   Comet Halley in 1986
   Enlarge
   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. Most
   spectacularly, the Giotto space probe, launched by the European Space
   Agency, made a close pass of the comet's nucleus. Other probes included
   the Soviet Union/France joint projects Vega 1 and Vega 2, and two
   Japanese probes, Suisei and Sakigake. The probes were unofficially
   known as the Halley Armada.

   It was Stephen Edberg (the 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.

   The comet was also observed from space by the International Cometary
   Explorer, which was in a solar orbit at the time. Originally
   International Sun-Earth Explorer 3 (ISEE-3), it was renamed and
   retooled after it was freed from its L1 Lagrangian point location to
   observe comet 21P/Giacobini-Zinner.

   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 Columbia 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.

   The Soviet Union's Salyut 7 space station was unoccupied during
   Halley's 1986 visit, and Mir, though launched during the visit, did not
   receive its first crew until later.

Designation

   This table sets out the 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.
   . Note, however, that the perihelion dates farther from the present are
   approximate, mainly because of uncertainties in the modeling of
   non-gravitational effects.
     * 1P/-239 K1 ( 25 May 240 BC)
     * 1P/-163 U1 ( 12 November 164 BC)
     * 1P/-86 Q1 ( 6 August 87 BC)
     * 1P/-11 Q1 ( 10 October 12 BC)
     * 1P/66 B1 ( 25 January 66 AD)
     * 1P/141 F1 ( 22 March 141)
     * 1P/218 H1 ( 17 May 218)
     * 1P/295 J1 ( 20 April 295)
     * 1P/374 E1 ( 16 February 374)
     * 1P/451 L1 ( 28 June 451)
     * 1P/530 Q1 ( 27 September 530)
     * 1P/607 H1 ( 15 March 607)
     * 1P/684 R1 ( 2 October 684)
     * 1P/760 K1 ( 20 May 760)
     * 1P/837 F1 ( 28 February 837)
     * 1P/912 J1 ( 18 July 912)

     * 1P/989 N1 ( 5 September 989)
     * 1P/1066 G1 ( 20 March 1066)
     * 1P/1145 G1 ( 18 April 1145)
     * 1P/1222 R1 ( 28 September 1222)
     * 1P/1301 R1 ( 25 October 1301)
     * 1P/1378 S1 ( 10 November 1378)
     * 1P/1456 K1 ( 9 June 1456)
     * 1P/1531 P1 ( 26 August 1531)
     * 1P/1607 S1 ( 27 October 1607)
     * 1P/1682 Q1 ( 15 September 1682)
     * 1P/1758 Y1, 1759 I ( 13 March 1759)
     * 1P/1835 P1, 1835 III ( 16 November 1835)
     * 1P/1909 R1, 1910 II, 1909c ( 20 April 1910)
     * 1P/1982 U1, 1986 III, 1982i ( 9 February 1986)
     * Next perihelion predicted 28 July 2061

   Note that perihelion dates 1607 and later are in the Gregorian
   calendar, whilst perihelion dates of 1531 and earlier are in the Julian
   calendar.

Meteor Showers

   Comet Halley is the parent body of several meteor showers - associated
   with the orbit of the comet inbound, and outbound. The showers are the
   Eta Aquarids in early May, the Orionids in late October.

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