Year of the Comet
Comet C/2011 L4 (PANSTARRS)

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Comet C/2012 S1 (ISON)

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Web Extras

Colliding galaxies electronically

Computer simulations reveal how normal galaxies get transformed as they fall under each other's gravitational spell.
By Richard Talcott
Published: July 25, 2005
Anytime astronomers witness a collision between two large galaxies, they see only a snapshot. Galaxies are so big, and gravity is such a weak force, that collisions take hundreds of millions — if not billions — of years from first brush to final outcome. Observers can see different galaxy pairs at different stages of interaction, but this gives only a vague sense of what goes on in individual cases.
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