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Halley's returns to the inner Solar System have been observed and recorded by astronomers since at least BC. Clear records of the comet's appearances were made by Chinese , Babylonian , and medieval European chroniclers , but, at those times, were not recognized as reappearances of the same object. The comet's periodicity was first determined in by English astronomer Edmond Halley , after whom it is now named. During its apparition, Halley's Comet became the first comet to be observed in detail by spacecraft , providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation.

The missions also provided data that substantially reformed and reconfigured these ideas; for instance, it is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy.

Spellings of Halley's name during his lifetime included Hailey, Haley, Hayley, Halley, Hawley , and Hawly , so its contemporary pronunciation is uncertain, but current bearers of this last name appear to prefer the version that rhymes with "valley". Halley was the first comet to be recognized as periodic. Until the Renaissance, the philosophical consensus on the nature of comets, promoted by Aristotle , was that they were disturbances in Earth's atmosphere.

This idea was disproved in by Tycho Brahe , who used parallax measurements to show that comets must lie beyond the Moon. Many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System.

His work on comets was decidedly incomplete. Although he had suspected that two comets that had appeared in succession in and were the same comet before and after passing behind the Sun he was later found to be correct; see Newton's Comet , [21] he was unable to completely reconcile comets into his model.

Ultimately, it was Newton's friend, editor and publisher, Edmond Halley , who, in his Synopsis of the Astronomy of Comets , used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits.

After a rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for Halley's prediction of the comet's return proved to be correct, although it was not seen until 25 December , by Johann Georg Palitzsch , a German farmer and amateur astronomer. It did not pass through its perihelion until 13 March , the attraction of Jupiter and Saturn having caused a retardation of days. It was also one of the earliest successful tests of Newtonian physics , and a clear demonstration of its explanatory power.

Some scholars have proposed that first-century Mesopotamian astronomers already had recognized Halley's Comet as periodic. Researchers in attempting to calculate the past orbits of Halley by numerical integration starting from accurate observations in the seventeenth and eighteenth centuries could not produce accurate results further back than due to a close approach to Earth in that year.

It was necessary to use ancient Chinese comet observations to constrain their calculations. Halley's orbital period has varied between 74—79 years since BC. The perihelion, the point in the comet's orbit when it is nearest the Sun, is just 0.

Its aphelion , or farthest distance from the Sun, is 35 AU roughly the distance of Pluto. Unusual 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. The passage was at a relative velocity of Observations conducted around the time of Halley's appearance in suggested that the comet could additionally perturb the Eta Aquariids meteor shower, although it might not be the parent of that shower.

Halley is classified as a periodic or short-period comet ; one with an orbit lasting years or less. Periodic comets have an average inclination to the ecliptic of only ten degrees, and an orbital period of just 6. Those resembling Halley, with orbital periods of between 20 and years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets.

The orbits of the Halley-type comets suggest that they were originally long-period comets whose orbits were perturbed by the gravity of the giant planets and directed into the inner Solar System.

Conversely the Jupiter-family comets are generally believed to originate in the Kuiper belt , [41] a flat disc of icy debris between 30 AU Neptune's orbit and 50 AU from the Sun in the scattered disc.

Another point of origin for the Halley-type comets was proposed in , when a trans-Neptunian object with a retrograde orbit similar to Halley's was discovered, KV 42 , whose orbit takes it from just outside that of Uranus to twice the distance of Pluto. It may be a member of a new population of small Solar System bodies that serves as the source of Halley-type comets. Halley has probably been in its current orbit for 16,—, years, although it is not possible to numerically integrate its orbit for more than a few tens of apparitions, and close approaches before AD can only be verified from recorded observations.

These orbital changes cause delays in its perihelion of four days, average. In , Boris Chirikov and Vitold Vecheslavov performed an analysis of 46 apparitions of Halley's Comet taken from historical records and computer simulations. These studies showed that its dynamics were chaotic and unpredictable on long timescales. These studies also showed that many physical properties of Halley's Comet dynamics can be approximately described by a simple symplectic map, known as the Kepler map.

The Giotto and Vega missions gave planetary scientists their first view of Halley's surface and structure. Like all comets, as Halley nears the Sun, its volatile compounds those with low boiling points, such as water , carbon monoxide , carbon dioxide and other ices begin to sublimate from the surface of its nucleus.

Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths, a phenomenon known as fluorescence , whereas dust particles scatter the solar light. Both processes are responsible for making the coma visible. Halley is the most active of all the periodic comets, with others, such as Comet Encke and Comet Holmes , being one or two orders of magnitude less active.

Subsequent observations showed Halley's deuterium ratio to be far higher than that found in Earth's oceans, making such comets unlikely sources for Earth's water. Giotto provided the first evidence in support of Fred Whipple 's " dirty snowball " hypothesis for comet construction; Whipple postulated that comets are icy objects warmed by the Sun as they approach the inner Solar System, causing ices on their surfaces to sublimate change directly from a solid to a gas , and jets of volatile material to burst outward, creating the coma.

Giotto showed that this model was broadly correct, [49] though with modifications. A comet was recorded in ancient Greece between and BC; its timing, location, duration, and associated meteor shower all suggest it was Halley.

He described it as brown in colour and the size of a wagon load. There are other explanations for the phenomenon, such as planetary conjunctions , and there are also records of other comets that appeared closer to the date of Jesus' birth.

This apparition was the only one to occur during ben Hananiah's lifetime. Chinese records also report it as the "broom star". It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire, and the Middle East; [10] Emperor Louis the Pious observed this appearance and devoted himself to prayer and penance, fearing that "by this token a change in the realm and the death of a prince are made known.

A comet appeared. In , 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 ; it was a bad omen for Harold, but a good omen for the man who defeated him, William the Conqueror. The comet is represented on the Bayeux Tapestry and described in the tituli as a star.

Surviving accounts from the period describe it as appearing to be four times the size of Venus and shining with a light equal to a quarter of that of the Moon. Halley came within 0. This appearance of the comet is also noted in the Anglo-Saxon Chronicle. Eilmer of Malmesbury may have seen Halley previously in , as he wrote of it in "You've come, have you?

You've come, 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. The Irish Annals of the Four Masters recorded the comet as "A star [that] appeared on the seventh of the Calends of May, on Tuesday after Little Easter, than whose light the brilliance or light of The Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards.

The apparition was recorded by the monk Eadwine. The apparition exhibited a fan tail similar to Eadwine's drawing. In , the year of Halley's next apparition, the Ottoman Empire invaded the Kingdom of Hungary , culminating in the Siege of Belgrade in July of that year. In , the humanist scholar Bartolomeo Platina wrote in his Lives of the Popes that, [78]. A hairy and fiery star having then made its appearance for several days, the mathematicians declared that there would follow grievous pestilence, dearth and some great calamity.

Calixtus, to avert the wrath of God, ordered supplications that if evils were impending for the human race He would turn all upon the Turks, the enemies of the Christian name. He likewise ordered, to move God by continual entreaty, that notice should be given by the bells to call the faithful at midday to aid by their prayers those engaged in battle with the Turk.

Platina's account is not mentioned in official records. In the 18th century, a Frenchman further embellished the story, in anger at the Church, by claiming that the Pope had "excommunicated" the comet, though this story was most likely his own invention. After witnessing a bright light in the sky which most historians have identified as Halley's Comet, Zara Yaqob , Emperor of Ethiopia from to , founded the city of Debre Berhan tr.

City of Light and made it his capital for the remainder of his reign. Halley, [82]. Halley's periodic returns have been subject to scientific investigation since the 16th century. The three apparitions from to were noted by Edmond Halley, enabling him to predict it would return. Newton also helped Halley get Flamsteed's data on the apparition. One difficulty was accounting for the effect of the planets, and Jupiter would delay Halley somewhat for At Markree Observatory in Ireland, a E.

Cooper used a Cauchoix of Paris lens telescope with an aperture of The coma was also sketched by F. An interview in , of someone who was a teenager at the time of the apparition had this to say: [87].

When the comet was first seen, it appeared in the western sky, its head toward the north and tail towards the south, about horizontal and considerably above the horizon and quite a distance south of the Sun. It could be plainly seen directly after sunset every day, and was visible for a long time, perhaps a month They go on to describe the comet's tail as being more broad and not as long as the comet of they had also witnessed.

Famous astronomers across the world made observations starting August , including Struve at Dorpat observatory, and Sir John Herschel, who made of observations from the Cape of Good Hope. At Yale college in Connecticut, the comet was first reported on 31 August by astronomers D.

Olmstead and E. A number of accounts of the apparition were made by those that survived until the return, where increased interest in the comet lead to them being interviewed. The time to Halley's return in would be only The approach, which came into naked-eye view around 10 April [62] and came to perihelion on 20 April, [62] was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained.

Indeed, on 19 May, Earth actually passed through the tail of the comet. The comet added to the unrest in China on the eve of the Xinhai Revolution that would end the last dynasty in As James Hutson, a missionary in Sichuan Province at the time, recorded,. The people believe that it indicates calamity such as war, fire, pestilence, and a change of dynasty. In some places on certain days the doors were unopened for half a day, no water was carried and many did not even drink water as it was rumoured that pestilential vapour was being poured down upon the earth from the comet.

The visitation is also recorded as being the travelling companion of Hedley Churchward , the first known English Muslim to make the Haj pilgrimage to Mecca. However, his explanation of its scientific predictability did not meet with favour in the Holy City.


Halley's Comet

Halley's returns to the inner Solar System have been observed and recorded by astronomers since at least BC. Clear records of the comet's appearances were made by Chinese , Babylonian , and medieval European chroniclers , but, at those times, were not recognized as reappearances of the same object. The comet's periodicity was first determined in by English astronomer Edmond Halley , after whom it is now named. During its apparition, Halley's Comet became the first comet to be observed in detail by spacecraft , providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation.


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