Comet
Comet
Comet (/ˈkɒmɪt/; from the Latin cometa and the Greek kometes, meaning "long-haired star") is a celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing away from the sun.
Etymology
The word "comet" comes from the Old English cometa borrowed from the Latin comēta, itself derived from the Greek kometes meaning "long-haired star". The ancient Greeks observed the fuzzy, glowing, hair-like appearance of comets in the sky, which is how they got their name.
Structure
A comet has a nucleus, a solid core of frozen water, various frozen gases, and rock. The nucleus is surrounded by a coma, a cloud of water vapor, carbon dioxide, and other gases that sublimate, or transform, from solid to gas when the comet is near the sun. When a comet gets close to the sun, the heat causes the nucleus to sublimate and create a visible atmosphere or coma, and often a tail.
Related Terms
- Asteroid: A small rocky body orbiting the sun. While similar to comets, asteroids are made up of metal and rock and lack a visible coma or tail.
- Meteor: A small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.
- Meteorite: A meteor that survives its passage through the earth's atmosphere and lands on the earth's surface.
- Meteoroid: A small body moving in the solar system that would become a meteor if it entered the earth's atmosphere.
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