comet

American  

[kom-it] / ˈkɒm ɪt /

noun

Astronomy.

comets plural

1. a celestial body moving about the sun, usually in a highly eccentric orbit, consisting of a central mass surrounded by an envelope of dust and gas that may form a tail that streams away from the sun.

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comet British  

/ ˈkɒmɪt, kɒˈmɛtɪk /

noun

1. a celestial body that travels around the sun, usually in a highly elliptical orbit: thought to consist of a solid frozen nucleus part of which vaporizes on approaching the sun to form a gaseous luminous coma and a long luminous tail

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comet Scientific  

/ kŏm′ĭt /

1. A celestial object that orbits the Sun along an elongated path. A comet that is not near the Sun consists only of a nucleus—a solid core of frozen water, frozen gases, and dust. When a comet comes close to the Sun, its nucleus heats up and releases a gaseous coma that surrounds the nucleus. A comet forms a tail when solar heat or wind forces dust or gas off its coma, with the tail always streaming away from the Sun.

2. ◆ Short-period comets have orbital periods of less than 200 years and come from the region known as the Kuiper belt. Long-period comets have periods greater than 200 years and come from the Oort cloud.

3. See more at Kuiper belt Oort cloud See Note at solar system

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comet Cultural  

1. An object that enters the inner solar system, typically in a very elongated orbit around the sun. Material is boiled off from the comet by the heat of the sun, so that a characteristic tail is formed. The path of a comet can be in the form of an ellipse or a hyperbola. If it follows a hyperbolic path, it enters the solar system once and then leaves forever. If its path is an ellipse, it stays in orbit around the sun.

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Discover More

Comets were once believed to be omens, and their appearances in the sky were greatly feared or welcomed.

The most famous comet, Comet Halley (or Halley's comet), passes close to the Earth roughly every seventy-six years, most recently in 1986.

Other Word Forms

Derived Forms

• cometary
  adjective
• cometic
  adjective
• cometical
  adjective
• cometlike
  adjective

Inflected Forms

Nouns

• comets
  plural

Etymology

Origin of comet

1150–1200; Middle English comete < Anglo-French, Old French < Latin comētēs, comēta < Greek komḗtēs wearing long hair, equivalent to komē-, variant stem of komân to let one's hair grow (derivative of kómē hair) + -tēs agent suffix

Explanation

A comet is a small, icy object that orbits the sun and has a long "tail" of gas. Some comets can be seen from Earth every few years, while others pass by once in a person's lifetime. Comets are made of ice, dust, and tiny pieces of rock, but to people on Earth, they look like streaks or smudges across the night sky. When the Earth's orbit takes it through one of these comets' tails, their dust burns up in our atmosphere and results in a meteor shower. In Old French, the word was comete, ultimately from a Greek root, kometes, which literally means "long-haired star."

Example Sentences

See Examples For:

comet comets

NASA's James Webb Space Telescope has captured the first mid-infrared chemical fingerprint of an interstellar object, providing new insights into the composition of comet 3I/ATLAS as it traveled away from the Sun.

From Science Daily ● Jun. 4, 2026

Its appearance only after the comet had already passed close to the Sun suggests the methane was buried beneath the surface.

From Science Daily ● Jun. 4, 2026

Water is less volatile than methane or carbon dioxide, which means its gas production shuts down more quickly as the comet cools.

From Science Daily ● Jun. 4, 2026

This behavior is expected as the comet receives less solar energy.

From Science Daily ● Jun. 4, 2026

But what if the flashes were instead caused by the impact of a small asteroid or a piece of a comet?

From "Cosmos" by Carl Sagan

From about 4.56 billion to 3.5 billion years ago, meteorites, micrometeorites and interplanetary dust particles from asteroids and comets repeatedly struck Earth.

From Science Daily ● Jul. 19, 2026

He’s standing across the net from comets barely half his age and smoking almost all of them.

From The Wall Street Journal ● Jul. 11, 2026

Together, the methane and carbon dioxide measurements point to a formation history that differs significantly from that of most comets that originated around our Sun.

From Science Daily ● Jun. 4, 2026

The ratio is much higher than what is typically seen in comets from our own solar system, with only a handful of known examples showing similar characteristics.

From Science Daily ● Jun. 4, 2026

There are no energy sources for comets or planets to be ejected by Jupiter.

From "Cosmos" by Carl Sagan