halley's comet

Halley's Comet is the only known short-period comet consistently visible to the naked eye from Earth, appearing approximately every 72 to 80 years, with the average orbital period around 76 years. It last appeared in the inner Solar System in 1986 and is expected to return in mid-2061. The comet is officially designated 1P/Halley and has been observed and recorded since at least 240 BC. It was named after the English astronomer Edmond Halley, who in 1705 recognized that its appearances were periodic and predicted its return. The comet has an irregular, elongated nucleus roughly 15 kilometers long and is composed of a mixture of volatile ices (water, carbon dioxide, ammonia) and dark dust, often described by the "dirty snowball" model. As it approaches the Sun, the ices sublimate, creating a coma and a long tail that extends millions of kilometers away from the Sun due to the solar wind. Halley's Comet has a retrograde orbit tilted about 18 degrees to Earth's orbit, taking it from within the orbit of Venus to beyond Neptune. Its orbital period varies due to gravitational interactions with planets but averages around 76 years. It is famous not only for its periodic returns but also for being the first comet to be studied up close by spacecraft, such as ESA's Giotto mission in 1986, which provided detailed data about its nucleus, structure, and behavior. Historically, the comet has been associated with significant events, such as its appearance in 1066 near the time of the Battle of Hastings, and it has been a source of fascination for astronomers and the public alike for centuries.