1P/ Halley Comet

Astronomical specifications: Discovery  December 25, 1758 Orbital characteristics: Distance from Sun   km Perihelion   (106 km) Aphelion   (106 km) Inclination   deg Eccentricity   Orbital periode rond Sun   days Main orbital speed   km/s Inclination to Sun equator   deg Physical characteristics: Dimensions   km Radius   km Surface area   km² Volume   106 km³ Mass   1024 kg Density   g/cm³ Equatorial surface gravity   m/s² Escape velocity   km/s Rotation period   days Surface temperature   K Axial tilt   deg Atmospheric composition

Credit: Anglo-Australian Observatory Halley's Comet (photo,1910)

Discovery:

Historical Highlights:

• -239 (240 BC): This is the first proven observation of 1P/Halley. The Chinese text Shih chi, which was written in -90 reported a "broom star" that "appeared in the east and then was seen in the north." The Chinese added that the comet was also seen during the lunar month of May 24 to June 23 in the west. Although this description is rough, calculations by various astronomers during the 1980s revealed the probable date of perihelion came sometime between -239 March 22 to May 25. The computed motion of the comet indicates it would have appeared in the east, moved through northern skies, and then would have been seen in the western sky.
• -163 (164 BC): The only accounts of this comet are found on two Babylonian cuneiform tablets. Tablet BMA 41462 says, "The comet which previously had appeared in the east in the path of Anu in the area of Pleiades and Taurus, to the west ... and passed along in the path of Ea." Tablet BMA 41628 is more damaged than the first, but contains the statement, "of Ea in the region of Sagittarius, 1 cubit in front of Jupiter, 3 cubits high toward the north." In 1984, F. R. Stephenson, K. K. C. Yau, and Herman Hunger wrote that both tablets give positions for the moon and several planets which indicates the lunar month of -163 October 21 to November 19. In addition, taking a cubit as 2.5°, they said the subsequent position of the comet from Jupiter indicated the comet probably passed perihelion sometime between November 9 and 26. The date of perihelion calculated by several astronomers during the 1980s generally fell within the range of October 23 to November 12. Although the Chinese records are the most complete and continuous accounts available on comet apparitions, there is no record of 1P/Halley for -163. In 1938, Homer H. Dubs offered a possible explanation. He wrote, "Since eclipses are also not mentioned during this decade, it looks as though the recorders of phenomena deliberately refused to record eclipses or comets, for the good reign of Emperor Wen made them think that Heaven was sending no admonitions, hence they concluded that there were no 'visitations.'"
• -86 (87 BC): The oldest source of information for this comet is the Babylonian cuneiform tablet designated BM 41018. During the early 1980s, Hermann Hunger identified a fragment of text that referred to a comet, and, in 1985, F. R. Stephenson, K. K. C. Yau, and Hunger were able to use additional astronomical references on the same Babylonian tablet to establish the year as -86. They were also able to establish that the comet was seen "day beyond day" during the lunar month of July 14 to August 11, and that another observation on August 24 reveals the comet had a tail 10° long. The Chinese text Han shu, which was written around AD 100, contains another observation of this comet. It says a "sparkling star" was seen "in the eastern quarter" during autumn, sometime within the month of August 10 to September 8.
• -11 (12 BC): The Chinese text Han shu, which was written around AD 100, reports this "sparkling star" was first detected in the morning sky on -11 August 26. The comet was then in "Tung-Ching", which is a group of stars in the constellation Gemini, and was "treading on Wu-Chu-Hou", which is another group of stars in Gemini. The date and location indicate a morning observation, and a likely precise date of August 25.8 (Universal Time). Following discovery the comet attained its maximum solar elongation of 83° on August 27. Because of the coming close approach to Earth, the comet's motion increased during the following days. Although not dated, the Chinese did note that the comet progressed at a rate of 6° or more prior to an observation made on September 7, at about the time it traversed "Hsien-Yüan" (an area within the constellations of Leo and Lynx). The comet attained it most northerly declination of +50° on September 8. The Han shu said the comet "appeared in the western quarter" on the night of September 6/7, implying an evening observation, but calculations indicate the comet would have been above the horizon only while evening twilight was still present. Because of its rapid motion it would have become an easier evening object possibly by September 8 and certainly by the 9th. F. Richard Stephenson and Kevin K. C. Yau (1985) suggested the latter date. The comet also entered the constellation Canes Venatici on the 9th. The comet headed rapidly southeastward. By September 11 it passed 33° from the sun. The final entry in the Han shu states that on the 56th day, or October 20, the comet "went out of sight with the Tshang-Lung," which is a group of stars in the constellation Scorpius. It was then very low in the western sky about a half hour after sunset.
• Closest Approach to Earth: The comet and Earth experienced their closest approach to one another on 837 April 10, when their separating distance equalled 0.0342 AU (3.2 million miles). It was seen worldwide for a few nights either side of this date, with a maximum tail length of 60 degrees. The comet had first been seen by the Chinese on March 21. It was then in Aquarius with a tail extending over 7 degrees toward Sagittarius. The Chinese were also the final observers when they reported it for the last time on April 28. Other cultures reporting the comet included the Japanese, Germans, and Muslims. The Japanese basically saw it around the time of the closest approach to Earth. The Germans first saw it during the first week of April and said it remained visible for 25 days. The Muslims did not give a day or month of visibility, but they noted it remained visible for "about forty nights." This duration is comparable to the 39 nights of visibility reported by the Chinese.
• Most Observed Apparition: The comet's recent return during the 1980s was the most observed return of any comet in history. The comet was first seen on 1982 October 16 and was last detected on 2003 March 8. The comet passed perihelion on 1986 February 9.46. This was not one of the more favorable appearances, as the maximum magnitude only reached 2.6 in early March 1986, while the tail grew to about 15 degrees by mid-March.
• The highlight of the 1986 apparition was the armada of space probes sent to visit the comet during February and March 1986. The European Space Agency's Giotto probe flew close enough to obtain an excellent image of the comet's nucleus.
• This comet will be farthest from the sun (aphelion) on December 9, 2023, at a distance of 35.14 AU (3.3 billion miles or 5.3 billion kilometers).

External links:

• Cometography.com: Comet 1P/Halley description.

Halley missions: