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Hands On Mineral Identification helps you to identify over 14,500 minerals! By M. Darby Dyar, Ph.D. See our DVD collection.
This is a drawing of how a comet behaves as it passes by the sun.
Click on image for full size
JPL

The Perihelion Passage of a Comet

Comets are disturbed from their orbits in the Oort Cloud and begin a passage into the solar system, spinning and tumbling as they come. The trajectory which they acquire can be hyperbolic, parabolic, or elliptic in shape. Only if a comet acquires an elliptic trajectory will it make repeated passes to the sun, as does Halley's comet every 76 years.

As the comet comes closer to the sun, near the region of space occupied by Mars it becomes warm enough for the comet to begin to evaporate. When evaporation begins, the coma and tail form.

This picture shows that, once the tails forms, it always points away from the sun. That means that the tail will point in different directions at different places in the comet's orbit.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA