Halley’s Comet

Named after the astronomer Edmond Halley, Halley’s Comet is a periodic comet that returns to earth after a period of 75 years. It was last witnessed in 1986 and is likely to appear again in the year 2061. Edmond Halley was curious to study the comets seen from earth in 1531 and then 1607 and 1682. His studies and research made him conclude that it was the same comet that returned to the planet earth intermittently. It was earlier designated and called the 1P/Halley. The first predicted perihelion was, however, in the year 1758.

Dimensions of Halley’s Comet and its Contents

Halley’s Comet was quite a mystery until discovered and was a freak among people after its discovery. The dimensions of this comet are 16 x 8 x 8 km (diameter). It is not very huge in size but is large enough to be clearly seen from the earth’s surface. The perihelion distance of this comet is 0.587 AU. Also, its orbital eccentricity is 0.967, and the orbital inclination is 162.24°. 

Halley’s Comet’s speed is 0.91 km per sec. However, the most famous appearance of this comet was in the year 1066, during the battle of Hastings. It stayed visible for a few weeks. Since then, many pieces of research have been conducted on this comet to learn more about it.

The origin of Halley’s Comet is said to be from the Kuiper’s belt. It is made up of hard rocks and ice compressed together. This is the leftover matter from the formation of the solar system some 4.6 billion years ago. Their pulling into the depths of the solar system has made them active. From the gases ejected out from the Halley’s Comet, a conclusion has been drawn that it is made of 80% water, 17% carbon monoxide, 4% carbon dioxide, etc., by proportion. The nucleus of Halley’s Comet is said to be 15 km long, 8 km wide, and 8 km thick. The dimensions say that Halley’s Comet isn’t a huge one. The average density of this comet is 0.6 g/cm3, and its average mass is 242.5 billion tons.

The Orbit of Halley’s Comet

The orbit of Halley’s Comet lasts for about 20 years and is thus a short-term orbit. The comets with a trajectory of hundreds of years have a long-term orbit. The comets originating from the Oort cloud have orbits that last for thousands of years. Moreover, a fantastic fact about Halley’s Comet is that it revolves around the sun in the opposite direction to the other planets. This makes its orbit retrograde. Also, the orbit is elliptical in shape and has a velocity quite high relative to earth (owing to its speed of 0.91 km per sec).

The Tail of Halley’s Comet and its Composition

Comets don’t need to always have a tail. However, Halley’s Comet has a tail that appears like a long, quite bright trail.

The tail is quite visible from the earth and is quite long. It is released from the nucleus of the comet and is made up of dust and gases compressed together. Halley’s Comet’s tail is often called the ‘coma.’ The comet has two parts of the tails made up of ionised gases and dust particles (this one is faint). The length of this coma is around 1,00,000 km which makes it quite detectable by the human eye. It contains many volatile gases such as methane, carbon dioxide, and ammonia.

This tail gets formed after the proximity of Halley’s Comet to the sun. The comet releases sublimating gases from its surface and gets knocked off its orbit slightly. This leads to the formation of the tail of the comet composed of ionised gases and particles of dust.

Conclusion

Halley’s Comet returns to earth after every 75 years and is next expected to be seen in the year 2061. It also has an ionised tail which is called the coma. The coma is formed when the comet comes closer to the sun. It has been created with the help of ice and matter, which had been left over after the solar system’s formation. With an orbital period of 20 years, it revolves around the sun in the opposite direction as the other planets in the solar system. It is not a very large comet, although it is large enough to be detected by people.