What is a comet?
"Comets are grouped according to their revolutionary paths around the sun. Some trace an elliptical orbit; others have a parabolic orbit and never return; yet others have a hyperbolic orbit, coming in a wide angle and disappearing in the same way. Comets with an elliptical orbit are cyclical comets and revolve continuously around the sun. A comet that approaches the sun for the first time is called a virgin comet."

"They say that a comet is actually a block of ice. It also contains gases and garbage, so is sometimes called a 'Dirty Snowman.' When this snowman approaches the sun, it simultaneously blows off gas and releases garbage, which become the comet's tail (in the direction away from the sun). The tail trails away from the sun, in the opposite direction from solar winds, or plasma flows emanating from the sun.

"When it approaches the sun, the comet pulls its tail behind it, but once it has circled the sun, it turns around and goes in the direction of the tail.

"The garbage travels at uniform velocity with the comet, but, due to different sizes of garbage, it seems to move more and more slowly. During repeated revolutions around the sun, the garbage assumes a belt-like shape within the comet's elliptical orbit.

"Interestingly, the belt-shaped orbit of the Swift-Tuttle comet crosses paths with the earth's orbit. On August 12 each year, the earth penetrates the stream of garbage, inducing many shooting stars. That is the Perseids meteor shower."
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