Halley’s Comet
Halley’s Comet is named after Edmond Halley, the English astronomer who was the first to understand that certain comets observed throughout history were in fact the same celestial object returning periodically. He studied observations of comets that appeared in 1531, 1607, and 1687. Halley realized that these appearances corresponded to the same comet returning regularly. In 1705, he calculated that this comet would return around 1758—and it did indeed reappear in 1758.
Halley’s Comet has been observed for more than 2,000 years.
In 240 BC, astronomers in China mentioned in their annals the appearance of a “broom star.” These observations were preserved in imperial chronicles and most likely correspond to a passage of Halley’s Comet.
In imperial China, observing the sky was an official function of the state. Astronomers worked for the emperor and recorded eclipses, comets, new stars, and planetary movements. An important mention appears in the chronicles known as the “Historical Records” (Shiji), written by Sima Qian, Grand Historian under Emperor Emperor Wu of Han. He describes a “broom star” observed in 240 BC.
In 87 BC, Chinese archives describe a bright star with a long tail, visible for several days or weeks, slowly moving across the sky.
On cuneiform tablets from Babylonia, dated to 164 BC, texts describe “stars with a tail.”
Theophanes the Confessor, a Byzantine historian, also mentions in his chronicle several appearances of comets associated with political or military unrest. Throughout history, these celestial objects were often interpreted as divine signs or omens of war.
A very famous passage of a celestial object is that of 12 BC. Some scientists believe that this appearance of Halley’s Comet could be linked to the Star of Bethlehem mentioned in the Gospel of Gospel of Matthew. This remains a debated hypothesis, as the exact date of the birth of Jesus Christ is uncertain and the biblical text does not clearly describe a comet:
Matthew 2:9
“The star they had seen in the East went ahead of them until it stopped over the place where the child was.”
The passage of the year 837 is one of the closest approaches to Earth in the comet’s history. Once again, precise Chinese chronicles describe it, mentioning an immense tail covering a large part of the sky.
In that year, 837, the Vikings launched raids across Europe. Louis the Pious ruled the empire founded by his father Charlemagne. In the Balkans, Khan Presian ruled the First Bulgarian Empire. The Bulgarians were in conflict with the Byzantine Empire and captured several cities in the region of Thrace. In China, the Tang Dynasty remained powerful and in control.
A major historical source is the Anglo-Saxon Chronicle. It mentions the appearance of a great comet in 1066, probably Halley’s Comet:
“That year, a wondrous star appeared in the sky.
It shone for a long time and had a great bright tail.”
Many medieval monks recorded celestial phenomena in their annals. For example, Orderic Vitalis, a Benedictine monk and historian, described the great comet of 1066.
This famous appearance of 1066 is also depicted on the Bayeux Tapestry, which tells the story of the Norman conquest of England.
The writer Mark Twain was born during the comet’s passage in 1835. He declared: “I came in with Halley’s Comet, and I expect to go out with it.” He died in 1910, the year of its next return.
Halley’s Comet reappeared on March 12, 1910—and a surprising wave of fear spread among people. Some newspapers of the time claimed that Earth might pass through the comet’s tail, which supposedly contained cyanogen gas (a toxic substance in laboratory conditions). This triggered rumors and the sale of various remedies. Merchants offered masks, bottles of “pure” air, and all kinds of fanciful solutions.
Halley’s Comet returns approximately every 75 to 76 years. Its long, luminous tail impresses sky observers. The last appearance of the comet was in 1986, and the next is expected in 2061.
During the 1986 passage, several probes studied the comet. The Giotto spacecraft, a mission of the European Space Agency, photographed the comet’s nucleus for the first time. Its diameter is about 15 km. It is composed of ice, dust, and rock, and produces a long luminous tail when the comet approaches the Sun.
The nucleus of a comet is made of ice (water, carbon dioxide, methane) mixed with dust. When it approaches the Sun, heat causes the ice to sublimate, turning directly from solid to gas. This gas carries dust particles into space. An envelope forms around the comet, followed by a tail stretching into space. A comet’s tail can reach several million kilometers, although its material is extremely diffuse.
