Planets have nearly circular orbits, but comets have elongated paths around the Sun. A comet is at "aphelion" when its orbit is farthest from the Sun. It is at "perihelion" when it is closest to the Sun. Due to angular momentum, a comet will travel fastest at perihelion and will slow down as it approaches aphelion.
Comets can be classified by their orbital period: that is, the time it takes them to make one complete trip around the Sun. Comets with short and intermediate orbital periods of less than 200 years – like Comet Halley, whose orbital period is 76 years – spend most of their time between Pluto and the Sun. These comets originally formed in the Kuiper Belt, but a gravitational "push" from the planets, especially Jupiter, swung them closer to the Sun.
A long-period comet will have an orbital period of more than 200 years. Comet Hale-Bopp, for example, completes an orbit about every 4,000 years. Scientists think that this type of comet spends most of its time way out in the Oort Cloud at the farthest edge of our solar system.
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