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

PANSTARRS information

Comet C/2012 S1 (ISON)

ISON information

Ask Astro

Published: January 25, 2010
Merging galaxies
The Milky Way and Andromeda galaxies will one day collide despite the fact that space-time itself is expanding. That's because local gravity overpowers the expansion and pull these galaxies toward one another.
Photo by Astronomy: Roen Kelly
Whether or not galaxies merge depends on how strong the gravitational attraction is between the galaxies and whether the universe's expansion is more powerful than gravity.
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