Named after Edmund Halley (1656-1742), the English astronomer who successfully predicted its appearance of 1758, Halley's Comet is the best-known and the brightest of the "short-period" comets from the Kuiper belt that visit the inner solar system in orbits of years or decades rather than the millennia of comets from the Oort Cloud.
Halley's Comet is expected to return in 2061.
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The usual pronunciation of
"Halley" is
'h�li',
to rhyme with "valley".
The pronunciation 'hejli', to rhyme with
"Bailey", is thought to have originated by relation with the rock group
Bill Haley and His Comets.
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Having perceived that the elements of the comet of 1682 were nearly the same as those of two comets which had appeared respectively in 1531 and 1607, Edmund Halley concluded that all the three orbits belonged to the same comet with a period of about 76 years.
After a rough estimate of the perturbations it must sustain from the attraction of the planets, he predicted its return for 1757, a bold prediction at that time, but justified by the event, for the comet again made its appearance as was expected, though it did not pass through its perihelion till the month of March 1759, the attraction of Jupiter and Saturn having caused, as was computed by Clairault previously to its return, a retardation of 618 days.
11BC and the Star of Bethlehem
It has been speculated that the "star of Bethlehem" which, according to the Gospel of Matthew, indicated the birth of Jesus Christ, was in fact Halley's Comet. The closest appearance of the comet, when it would have been visible to the naked eye, would have been 11 BC - five years before the most likely date for the birth of Jesus.
1066
Halley's comet was observed in 1066, the year of the Norman Conquest of Saxon England, and considered to be an omen. Rightly or wrongly, Duke William of Normandy claimed that Harold Godwinson, had sworn on the bones of a saint that he should succeed Edward the Confessor to the throne of England. On The Confessor's death in 1066, the witan elected Harold as King Harold II. On the grounds of the brocken "promise" and, not least, because Archbishop Stigand had recieved the pallium from the Antipope, Duke William's invasion of England had the sanction of the Pope.
Since ancient times, the appearance of comets had been seen as the sign of the death of a king or the fall of a country. As invasion plans advanced the appearance of Halley's Comet seemed to the Norman's and their supporters as a certain sign that England and its new king would fall under their onslaught. The Saxons of England themselves could not have been unaware of the superstitions concerning comets.
The comet, albeit in highly styalised form is depicted in the Bayeux Tapestry, and the accounts of its appearance 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.
History makes no mention of Halley's Comet again until the year 1456.
1456
The record of the appearnce of the comet in 1456 is its first mention in history since 1066. In that year it passed very near to the earth and its tail extended over 60° of the heavens in the form of a sabre.
1835
As it returned to its perihelion in 1835, Halley's comet was well observed in almost every observatory on earth but its brightness was far from comparing with the glorious accounts of its former apparitions.
That the dimming of the comet should have been due to the process of dissipation does not seem possible in so short a period so we must therefore consider either that either the earlier accounts are greatly exaggerated, or that the brightness of the comet is subject to changes from some cause as yet unkown to us.
Previous appearances of Halley�s comet have been calculated by J R Hind, and more recently by P H Cowell and A C D Crommelin of Greenwich, the latter having carried the comet back to 87 BC with certainty, and to 240 BC with fair probability.
1910
The relatively close approach to Earth of the comet in 1910 was notable for several reasons; its proximity made it a spectacular sight; it was the first time the comet was photographed, and the Earth passed through the difuse tail of the comet.
The approach of Halley's comet was detected by Max Wolf at Heidelberg on plates exposed on September 11th, 1909, and subsequently on a Greenwich plate exposed on September 9th. It grew steadily brighter till it was easily visible to the naked eye.
The Earth passed through the tail of the comet on May 18th, 1910, to massive media attention and dire predictions off mass poisoning or some form of intoxication as the CN radical had been detected in cometary tails by spectrocscopy - the predictions of doom abounded despite the fact that the miniscule concentrations of the toxin could only have been a fraction of that caused by industrial pollution.
The close approach of the comet was used as an opportunity to establish its composition by spectrography.
1986
While the 1985/1986 approach of the comet, barely visible to the naked eye, produced nothing like the public attention of 1910, it afforded scientists an unprecedented opportunity to study the famous heavenly body.
Several probes were launched to study Halley's comet at close quarters, most spectacularly the European Space Agency's Giotto space probe which made a close pass of the comet's nucleus. Other probes included the Soviet Vega 1 and Vega 2 and the Japanese probes Suisei and Sakigake.
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If the passing of the Earth through the comet's tail in 1910 did not produce the anticipated mass intoxication, the effect seems to have caught up 76 years later with the usually sober Financial Times which normally used the advertising slogan "No FT - No Comment " in 1986 when it imitated its tabloid cousins by replacing the word "Comment " in one of its advertisements with a picture of the comet - the connection being, presumably, the "spaced-out " orbit of the heavenly body concerned.
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2061
Halley's Comet is expected to return in 2061.
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