Halley’s Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years.
Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime. Halley last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061 to 2062.
Halley’s returns to the inner Solar System have been observed and recorded by astronomers since at least 240 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 1705 by English astronomer Edmond Halley, after whom it is now named.
During its 1986 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.
These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple’s “dirty snowball” model, which correctly predicted that Halley would be composed of a mixture of volatile ices—such as water, carbon dioxide, and ammonia—and dust.
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.
Computation of orbit
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 1577 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.
In 1687, Sir Isaac Newton published his Philosophiæ Naturalis Principia Mathematica, in which he outlined his laws of gravity and motion. His work on comets was decidedly incomplete. Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun, he was unable to completely reconcile comets into his model.
Ultimately, it was Newton’s friend, editor, and publisher, Edmond Halley, who, in his 1705 Synopsis of the Astronomy of Comets, used Newton’s new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits.
Having compiled a list of 24 comet observations, he calculated that the orbital elements of a second comet that had appeared in 1682 were nearly the same as those of two comets that had appeared in 1531 (observed by Petrus Apianus) and 1607 (observed by Johannes Kepler).
Halley thus concluded that all three comets were, in fact, the same object returning about every 76 years, a period that has since been found to vary between 74 and 79 years. After a rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758.
While he had personally observed the comet around perihelion in September 1682, Halley died in 1742 before he could observe its predicted return.
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. It did not pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused a retardation of 618 days.
This effect was computed prior to its return (with a one-month error to 13 April) by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute. The confirmation of the comet’s return was the first time anything other than planets had been shown to orbit the Sun.
It was also one of the earliest successful tests of Newtonian physics, and a clear demonstration of its explanatory power. The comet was first named in Halley’s honor by French astronomer Nicolas-Louis de Lacaille in 1759.
Some scholars have proposed that first-century Mesopotamian astronomers already had recognized Halley’s Comet as periodic. This theory notes a passage in the Bavli Talmud that refers to “a star which appears once in seventy years that makes the captains of the ships err.”
Researchers in 1981 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 837 due to a close approach to Earth in that year. It was necessary to use ancient Chinese comet observations to constrain their calculations.
Prior to 1066
Halley may have been recorded as early as 467 BC, but this is uncertain. A comet was recorded in ancient Greece between 468 and 466 BC; its timing, location, duration, and an associated meteor shower all suggest it was Halley.
According to Pliny the Elder, that same year a meteorite fell in the town of Aegospotami, in Thrace. He described it as brown in color and the size of a wagon load. Chinese chroniclers also mention a comet in that year.
The first certain appearance of Halley’s Comet in the historical record is a description from 240 BC, in the Chinese chronicle Records of the Grand Historian or Shiji, which describes a comet that appeared in the east and moved north. The only surviving record of the 164 BC apparition is found on two fragmentary Babylonian tablets, now owned by the British Museum.
The apparition of 87 BC was recorded in Babylonian tablets which state that the comet was seen “day beyond day” for a month. This appearance may be recalled in the representation of Tigranes the Great, an Armenian king who is depicted on coins with a crown that features, according to Vahe Gurzadyan and R. Vardanyan, “a star with a curved tail that may represent the passage of Halley’s Comet in 87 BC.”
Gurzadyan and Vardanyan argue that “Tigranes could have seen Halley’s Comet when it passed closest to the Sun on August 6 in 87 BC” as the comet would have been a “most recordable event“; for ancient Armenians it could have heralded the New Era of the brilliant King of Kings.
The apparition of 12 BC was recorded in the Book of Han by Chinese astronomers of the Han Dynasty who tracked it from August through October. It passed within 0.16 AU of Earth.
According to the Roman historian Cassius Dio, a comet appeared suspended over Rome for several days portending the death of Marcus Vipsanius Agrippa in that year.
Halley’s appearance in 12 BC, only a few years distant from the conventionally assigned date of the birth of Jesus Christ, has led some theologians and astronomers to suggest that it might explain the biblical story of the Star of Bethlehem.
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.
If, as has been suggested, the reference in the Talmud to “a star which appears once in seventy years that makes the captains of the ships err” refers to Halley’s Comet, it may be a reference to the 66 AD appearance, because this passage is attributed to the Rabbi Yehoshua ben Hananiah. This apparition was the only one to occur during ben Hananiah’s lifetime.
The 141 AD apparition was recorded in Chinese chronicles. It was also recorded in the Tamil work Purananuru, in connection with the death of the south Indian Chera king Yanaikatchai Mantaran Cheral Irumporai.
The 374 AD and 607 approaches each came within 0.09 AU of Earth. The 684 AD apparition was recorded in Europe in one of the sources used by the compiler of the 1493 Nuremberg Chronicles; it is the oldest-known image depicting a comet. Chinese records also report it as the “broom star”.
The 451 AD apparition was said to herald the defeat of Attila the Hun at the Battle of Chalons. In 837, Halley’s Comet may have passed as close as 0.03 AU (3.2 million miles; 5.1 million kilometers) from Earth, by far its closest approach.
Its tail may have stretched 60 degrees across the sky. It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire, and the Middle East; 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.” In 912, Halley is recorded in the Annals of Ulster, which states
“A dark and rainy year. A comet appeared.”
In 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; 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 0.10 AU of Earth at that time.
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 afterward.”
Chaco Native Americans in New Mexico may have recorded the 1066 apparition in their petroglyphs.
The 1145 apparition was recorded by the monk Eadwine. The 1986 apparition exhibited a fantail similar to Eadwine’s drawing.
Some claim that Genghis Khan was inspired to turn his conquests toward Europe by the 1222 apparition. The 1301 apparition may have been seen by the artist Giotto di Bondone, who represented the Star of Bethlehem as a fire-colored comet in the Nativity section of his Arena Chapel cycle, completed in 1305. Its 1378 appearance is recorded in the Annales Mediolanenses as well as in East Asian sources.
In 1456, 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 a papal bull, Pope Callixtus III ordered special prayers to be said for the city’s protection. In 1470, the humanist scholar Bartolomeo Platina wrote in his Lives of the Popes that:
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.
Halley’s apparition of 1456 was also witnessed in Kashmir and depicted in great detail by Śrīvara, a Sanskrit poet and biographer to the Sultans of Kashmir. He read the apparition as a cometary portent of doom foreshadowing the imminent fall of Sultan Zayn al-Abidin (AD 1418/1420–1470).
After witnessing a bright light in the sky which most historians have identified as Halley’s Comet, Zara Yaqob, Emperor of Ethiopia from 1434 to 1468, founded the city of Debre Berhan (tr. City of Light) and made it his capital for the remainder of his reign.
Halley’s periodic returns have been subject to scientific investigation since the 16th century. The three apparitions from 1531 to 1682 were noted by Edmond Halley, enabling him to predict it would return.
One key breakthrough was Halley was able to talk with Newton, about his ideas about the laws of motion, and Newton also helped Halley get Flamsteed’s data on the 1682 apparition.
By studying data in 1531, 1607, and 1682 comets, he came to the conclusion these were the same Comet and presented his findings in 1696.
One difficulty was accounting for the effect of the planets, and Jupiter would delay Halley somewhat for 1759. In the decades that followed, more refined mathematics would be worked on, notable by Paris Observatory; the work on Halley also provided a boost to Newton and Kepler’s rules for celestial motions.
Halley’s Comet in 1910
The 1910 approach, which came into naked-eye view around 10 April and came to perihelion on 20 April, was notable for several reasons: it was the first approach of which photographs exist and the first for which spectroscopic data were obtained.
Furthermore, the comet made a relatively close approach of 0.15 AU, making it a spectacular sight. Indeed, on 19 May, Earth actually passed through the tail of the comet.
One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen, which led astronomer Camille Flammarion to claim that, when Earth passed through the tail, the gas “would impregnate the atmosphere and possibly snuff out all life on the planet.”
His pronouncement led to panicked buying of gas masks and quack “anti-comet pills” and “anti-comet umbrellas” by the public. In reality, as other astronomers were quick to point out, the gas is so diffuse that the world suffered no ill effects from the passage through the tail.
The comet added to the unrest in China on the eve of the Xinhai Revolution that would end the last dynasty in 1911. 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 rumored that pestilential vapor was being poured down upon the earth from the comet.”
The 1910 visitation is also recorded as being the traveling 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 favor in the Holy City.
The comet was also fertile ground for hoaxes. One that reached major newspapers claimed that the Sacred Followers, a supposed Oklahoma religious group, attempted to sacrifice a virgin to ward off the impending disaster, but were stopped by the police.
American satirist and writer Mark Twain were born on 30 November 1835, exactly two weeks after the comet’s perihelion. In his autobiography, published in 1909, he said:
I came in with Halley’s comet in 1835. It is coming again next year, and I expect to go out with it. It will be the greatest disappointment of my life if I don’t go out with Halley’s comet. 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 21 April 1910, the day following the comet’s subsequent perihelion. The 1985 fantasy film The Adventures of Mark Twain was inspired by the quotation.
Halley’s 1910 apparition is distinct from the Great Daylight Comet of 1910, which surpassed Halley in brilliance and was actually visible in broad daylight for a short period, approximately four months before Halley made its appearance.
Halley’s Comet in 1986
Halley’s 1986 apparition was the least favorable on record. The comet and Earth were on opposite sides of the Sun in February 1986, creating the worst viewing circumstances for Earth observers for the last 2,000 years.
Halley’s closest approach was 0.42 AU. Additionally, with increased light pollution from urbanization, many people failed to even see the comet. It was possible to observe it in areas outside of cities with the help of binoculars.
Further, the comet appeared brightest when it was almost invisible from the northern hemisphere in March and April 1986.
Halley’s approach was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the 5.1 m Hale telescope at Mount Palomar and a CCD camera.
The first person to visually observe the comet on its 1986 return was amateur astronomer Stephen James O’Meara on 24 January 1985. O’Meara used a home-built 24-inch telescope on top of Mauna Kea to detect the magnitude 19.6 comet.
On 8 November 1985, Stephen Edberg (then serving as the Coordinator for Amateur Observations at NASA’s Jet Propulsion Laboratory) and Charles Morris were the first to observe Halley’s Comet with the naked eye in its 1986 apparition.
Although Halley’s Comet’s retrograde orbit and high inclination make it difficult to send a space probe to it, the 1986 apparition gave scientists the opportunity to closely study the comet, and several probes were launched to do so.
The Soviet Vega 1 started returning images of Halley on 4 March 1986, and the first-ever of its nucleus, and made its flyby on 6 March, followed by Vega 2 making its flyby on 9 March. On 14 March, the Giotto space probe, launched by the European Space Agency, made the 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.
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.
The comet was also observed from space by the International Cometary Explorer (ICE). 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. ICE made its closest approach on 28 March 1986.