Brandt, John C. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado.
Last reviewed:February 2019
Show previous versions
- Discovery and designation
- Collisions with other bodies
- Coma and jets
- Hydrogen cloud
- Comet populations in the solar system
- Fate of comets
- Notable space missions to comets
- Links to Primary Literature
- Additional Readings
A common kind of celestial object made of rock and ice that typically moves in a closed orbit around a star, such as the Sun, and appears as a hazy streak when viewed in Earth’s skies. Physically, a comet is a small, solid body, termed the nucleus, which comes in a range of sizes but is typically of the order of 3 km (2 mi) in diameter. Although it is mostly rocky, a comet’s nucleus contains a high fraction of icy substances, leading to popular descriptions of comets as “dirty snowballs” or “icy dirtballs.” Comets exhibit their iconic morphology of a bright ball, called the coma, followed by a streaking tail or tails (Fig. 1) when these ices heat up and sublimate during cometary approaches to the Sun. Compared to the orbits of planets and asteroids, comets’ orbits are more eccentric and have a much greater range of inclinations to the ecliptic (the plane of the Earth’s orbit). About 10 reasonably bright comets are discovered or rediscovered each year. On average, one comet per year is bright enough to be visible to the unaided eye and to generate interest among the public as well as the astronomical community. See also: Asteroid; Astronomy; Earth; Ecliptic; Heat; Planet; Sublimation; Sun
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information