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Name: Ashley
Status: student
Age: 11
Location: N/A
Country: N/A
Date: 1999 - 2000

When is a comet's tail in front of the comet instead of behind?

When the comet is receeding from the sun (going away), the tail is in front of the nucleus. The solar wind acting on the nucleus is sending material away from the sun, and much faster than the comet is moving.



The phrase "in front of" that you use is a bit misleading. It is more correct to say that the tail of the comet will always face away from the sun. The tail of the comet is the result of energy from the sun reaching the comet and either melting water ice or sublimating sold carbon dioxide (dry ice) along with the subsequent release of organic molecules which had been held in the structure. Since the enregy from the sun emantes from the sun to other universal bodies, the tail which results from the impact of that energy will also travel away from the sun. Note that as the comet approaches the sun (flying in its direction, but not directly at it) the comet's tail will face back, approximately opposite the direction of travel. The more the comet's direction is not directly towards the sun, the greater the deviation from directly behind the comet the tail will be. After passing the sun, assuming there is still more of the comet left to continue traveling, the tail will continue to face away from the sun, towards the outer part of our solar system.

To try to depict this graphically:
     O       o--       

with the large O representing the sun, and the small o representing the comet. Note the tail faces away from the sun

note, in this case, the comet is not headed directly towards the sun, but the comet's tail again faces away from the sun


Note, as the comet passes the sun, the tail continues to point away from the sun
     ---o         O 

The comet has now passed the sun, and the tail still faces away from the sun

Please note, in each of the above depictions, the direction of comet travel is right to left, and I am a bit limited in the document with the ability to align exactly what would be seen.

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A comet's tail points away from the Sun, because it is blown that direction by ions streaming out from the Sun. So, whenever a comet is moving away from the Sun, its tail will stream ahead of it.

Richard Barrans Jr., Ph.D.

When the comet comes near the Sun, it gets hot. Some of the comet is ice and frozen gases. This stuff melts in the heat of the Sun, and makes a cloud around the comet head. The heat from the Sun makes the cloud boil off in the direction away from the Sun. So, the tail always points away from the Sun. If the comet is coming towards the Sun, then the tail points "behind" the comet. If the comet is going away from the Sun, the tail points "in front of" the comet. If the comet is going past the Sun, the tail points "on the side" of the comet.

Dr. C. Grayce

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