A British scientist called Edmond Halley, who observed the comet in 1682, was the first person to establish its periodic reappearance after every 75 - 76 years. He studied the comet, and quite accurately predicted that it had earlier appeared in 1531 and in 1607. It was named 'Halley' in his honor, and was observed again in 1758 as stated by him. It was last seen in February 1986. However, this was not the first time the comet was in focus. The first recorded sighting was way back in 240 BC by the Chinese, and was mentioned in a chronicle, 'Records of the Great Historian'. The comet also finds a mentioning in a Babylonian clay inscription of 164 BC.
It has always been a subject of great interest, since it was believed to have an influence on the contemporary events. Armenian king Tigranes II, had its image printed on the coins issued in his regime, after it was sighted in 87 BC. Therefore, even though the recurrence of the comet was an unknown fact, people were fascinated by its appearance. The bright star that appeared in the night sky in 12 BC, coinciding with the birth of Jesus, is widely believed to be the Halley's comet. Giotto Di Bondone, the famous Italian painter, who lived before the Renaissance era, painted it in his work 'The Star of Bethlehem' in the Nativity, in 1305. He had seen the comet appear in 1301, and was impressed by the spectacle.
In the middle ages, the appearance of a comet was considered to be a warning sign of a forthcoming danger. The most famous incident of spotting a comet during this period was in 1066, before the Battle of Hastings. King Harold who had lost the battle, was believed to have seen the comet, due to which he was cursed. In fact, the Bayeux Tapestry in Normandy, France, signifies the Norman victory in this battle with an image of King Harold looking at the comet in the sky. In 1456, Pope Calixtus III had condemned its appearance by considering it to be an evil omen. Three years prior to this, Europe was defeated by the Ottoman Empire.
Human beings have always blamed celestial phenomena, whenever they have not been able to explain the causes of certain unfavorable events. Historically, the presence of a comet in the night sky was commonly cited as the reason behind difficult situations that were beyond the reasoning of the common man. A French physician called Ambroise, had described the pitiful conditions of middle ages, when a comet was seen just before the spread of a big epidemic. According to him, some people were scared to death, while others fell sick on seeing the comet. It was believed to be some 'evil form' leaving behind a trail of blood, believed to be a sign of misery.
In the 16th and the 17th century, scientists learned to calculate the speed and distance at which comets travel around the Sun. Once Edmond Halley had established the year of its reappearance, Halley's comet became a matter of great interest. Although, he didn't live to see his prediction coming true, his observation had a significant impact on the way society perceived comets. The sighting of such bodies, especially Halley's comet, became less of a concern, and more of a curiosity among people. Once people realized that they are orbiting bodies just like other planets, they became less apprehensive on the arrival of a comet in the Earth's visibility zone. The change in the attitude of the people was seen in the depiction of the comet in contemporary pictures. Halley's comet was a subject of scientific study, and was depicted as a beautiful heavenly body in the sky.
Famous American writer Mark Twain was born in 1835, the year when Halley's comet had appeared. He predicted in 1909 that since he had 'come' with the comet he will 'go out' with it. Sure enough, he passed away a year after the comet reappeared in 1910. In the 1900s, it had appeared twice; once in 1910 and then in 1986.
Further studies gave us a deep insight into the structure, composition, and the orbital journey of many different comets. Halley's comet has one of the shortest orbital paths. It is classified as a short period comet, i.e., comets having an orbit period of 200 years or less. It belonged to the long period class, but due to the gravitational force of planets, its orbit shortened over a period of time. Today, it is known that comets like 'Hale Bopp' that appeared in 1997, will reappear after 4200 years! Thus, Halley's comet is the most frequently spotted one. In 1986, it was subjected to its biggest scrutiny ever. Five spacecrafts from The European Space Agency, Japan, and the USSR were launched to study its surface.
Structure and Composition of Halley's Comet
Halley's comet is a big mass of ice and dust, having an elliptical orbit and shaped like a peanut. It has a highly elongated orbit, taking it very close to the Sun. It flings off far in the outer solar system, similar to a slingshot motion. The composition is mainly of water, sodium monoxide, methane, ammonia, hydrocarbons, iron, and sodium. Its closest distance from the Sun was found to be just 0.6 AU (astronomical unit), and the farthest distance was calculated to be 35 AU, roughly the same distance as that of Pluto. It orbits the Sun in a retrograde, or in the direction opposite to that of the planets' revolution. The speed with respect to the Earth is quite high, since it is highly eccentric and inclined. The day time is relatively more on its surface, and its maximum temperature rises up to 77 degrees Celsius.
Due to its large size, and a well-defined and regular orbit, it was easy for the probe missions to photograph it closely, and study its surface. The mass of the comet is 1.7×1015 kilograms. Winds blowing near its surface are so strong that 1 gram particle of dust, which hit the Giotto space probe, briefly destabilized it. This comet will next appear in 2062.
Comets have always been a fascination for human beings, and will continue to mesmerize future generations, as we discover more interesting facts about these spectacular fireballs.