When Will Halley’s Comet next Appear?
Halley’s Comet appeared in 1910, then in 1986 and will next appear in mid-2061, during that most recent visit, five spacecraft from the USSR, Japan, and the European Community journeyed to Comet Halley. It is the most famous of all periodical comets—those which move round the sun and reappear in our skies at known intervals. 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 were not recognized as reappearances of the same object at the time.
The comet is named after the British astronomer, Edmund Halley (1656-1742) who observed it in 1682 and determined the comet’s periodicity in 1705. He predicted accurately that it would return in 1758, but died too soon to see it. Gravity from other bodies in the solar system affects its orbit. Over the centuries, Halley’s orbital period has varied from 76 years to 79.3 years. Comets have been called the stray members of the solar system, but the description is misleading as a comet’s orbit can be calculated like that of a planet, though they may appear unexpectedly.
A comet consists of a mixture of dust, frozen gases and ice, and resembles a gigantic dirty snowball. When near the sun, the heat vaporizes some of the gas and ice. The clouds of gas and dust released forms a visible tail. Although a comet may be larger than the Earth or even Jupiter, it contains only a small quantity of matter. This lack of substances makes it invisible until relatively close to the Earth. A comet’s tail always points away from the sun, probably because of the intense radiation which repels the tail’s tiny particles. Its orbit is much more elliptical than that of a planet, and therefore is only visible at certain times, when near the Earth. Comet Halley will return to the inner solar system in the year 2061, with a perihelion passage in early 2062.
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.