One of the most well known celestial bodies that appear in our night sky every 74 to 79 years is Halley’s Comet. It has regularly visited Earth and the rest of the inner solar system since 240 B.C. and it originates from an area outside of the orbit of Pluto called the Oort Cloud. Most comets who have an orbit of more than 200 years come from this area of the galaxy with comets whose orbit is less than 200 years originating from the Kuiper belt near Pluto. Under this convention, Halley’s Comet should be considered a ‘short period comet’, but astronomers believe that it has been irrevocably caught by the gravity of the larger planets in our solar system.
This particular comet had long been seen before it was named after Edmund Halley with some of the oldest recording sightings dating back to 240 B.C. in China. It is conceivable that the comet could’ve been watched by ancient man as early as 467 B.C. However, it was Edmund Halley that first came up with the concept that the comet would return to Earth based on observations of other comets he had made and the similarity of their orbits. A friend of Isaac Newton and well versed in the new laws of gravity, he used these laws in conjunction with the gravitational forces that would be exerted on the comet by Jupiter and Saturn to predict that it would return in 1758.
Halley made his prediction in 1705 and unfortunately he died in 1742, sixteen years prior to his prediction. But Halley’s calculations had been correct on Christmas night in 1758 the comet reappeared just like Halley had said. From that day, it has been known as Halley’s Comet and based on Halley’s calculations it has reappeared every 74 to 79 years since. Not only did Halley’s calculations help future astronomers track the comet, it also helped solidify Newton’s gravitational theories.
The appearance and subsequent tracking of Halley’s Comet has helped astronomer’s learn quite a bit about our solar system. The comet has an orbit that dips below the elliptic of the planets orbits when it is in the outer solar system and its furthest orbital point is between Neptune and Pluto. It also has a clockwise orbit while the planets have a counter-clockwise orbit around the sun.
Halley’s Comet was last seen from Earth in 1986. It is scheduled to reappear in our part of the solar system sometime in the middle of 2061.
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