We have heard of the name ‘Halley’s comet’ many times, as the comet is the most famous “Periodic” comet. The reason why it’s termed the periodic comet is that it comes to the Earth’s vicinity about every 76 years.
Until English astronomer Edmond Halley (1656-1742) predicted, it was believed that the comet passes our solar system only once. However, Halley applied Isaac Newton’s theories of gravitation and planetary motions & in 1705 computed the orbits of many comets that have passed the solar system before. He found striking similarities between the comets that had been observed in 1531, 1607, 1682. These similarities were found in the orbits of these comets and thus, Halley concluded that all these comets were a single comet. He was proved right by the return of the comet in 1759, 16 years after his death and thus, to honour him the comet was named after him.Halley’s comet has dimensions of about 15 kilometres by 8 kilometres. The albedo of the comet is 0.03, which implies that it only reflects a total of 3% of the light that falls onto it, thus making it one of the least reflective objects present in the solar system. The orbit of the comet is very unusual. Especially, considering that it is a short-period comet. With the orbit being tilted at an angle of 18 degrees as compared to that of the Earth, it also moves in the opposite direction of the Earth’s motion around the Sun. Its orbit period is of about 76 Earth years and this correlates to 12.2 billion kilometres to an orbital circumference around the Sun. but this period may vary due to the gravitational effects of the other planets. Halley’s comet has many times been associated with meteor showers. Even though the comet gets close to the Earth once a few decades, its remnants are visible in the form of meteor showers each year. The Eta Aquarids in May and the Orionids in October are examples of such meteor showers caused due to the spray of rock and ice debris into space from the comet’s nucleus.
Every time any comet orbits around the sun, it is reported to lose an estimate of 3 to 10 feet of the surface material of its nucleus. Hence, as time passes and the comet keeps ageing & it will eventually dim in appearance. It might end up losing all the ices in its nucleus. At this stage, the tail also disappears and the comet either ends up being a rocky mass or dissipates into dust. According to scientists, as of now, Halley’s comet hasn’t shown any sign of ageing, so it’s safe to predict that Halley’s comet will not be diminishing any time soon.
The last time that the comet was observed was 1986, and it is projected to return in 2061.
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