Halley's Comet

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Out of all the phenomena that occur within our galaxy, comets are one of the most amazing. Being the most well-known, it’s safe to say that when talking about these small bodies, Halley’s Comet comes to mind. Even though it only graces us with its presence about once every 75 years, Halley’s Comet continues to astonish us to this day. Despite centuries of observation, there is still much to learn about comets. Comets consist of three main parts: the tail, coma, and nucleus. The tail, which is made of a narrow column of dust and gas, is the largest part of the comet and can extend up to 100 million kilometers across the inner solar system. It is only visible when the comet is within 3 AU's of the Sun. The coma is a cloud of gas that can have a diameter of 100,000 kilometers, and it is created by the heat of the Sun boiling the core or nucleus of the comet. The nucleus is often referred to as a giant "iceberg" or "dirty snowball" and is a block of ice with an irregular mass and a diameter of about 10 kilometers. The Oort cloud, which is an assemblage of trillions of icy bodies, is a spherical shell that completely surrounds the Solar System and is believed to be the origin of long-period comets that now orbit the Sun. Short-period comets come from the Kuiper Belt, a doughnut-shaped ring extending just beyond the orbit of Neptune from about 30 to 55 AU. Astronomers believe that Halley's Comet, which is considered a short-period comet, also originates from the Kuiper Belt. Halley's Comet has a nucleus with dimensions of 10 x 5 x 5 miles and travels at a speed of 157,838 miles per hour, making it one of the speediest comets in the night sky. Although spectators on Earth can only view Halley once every 75 years or so, remnants of the famous comet are evident more frequently. Earth passes through the dust debris of Halley once in May and again in October during the meteor showers Eta-Aquarid and Orionid, respectively. Halley's Comet has been observed once every 75.3 years for the last 2,200 years, and the earliest recorded sighting was in the year 240 B.C. by the Chinese. Babylonian tablets show visits by Halley recorded in 164 B.C. and again in 87 B.C.

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