Near-future astronomic events that could threaten Earth What kinds of astronomical events can pose a serious threat to life on Earth in the near future (1000-10,000 years). If there are none in the near future, when is the soonest event that is predicted to threaten life on Earth? 

I am ignorant about astrononomy and so far I have only thought of an asteroid collision, solar flares, and effects from the sun dying in several billion years (and a visit by some hostile aliens).
Essentially, anything could happen! We can't really predict events such as you've described.
The only event we can really be certain of is that the Sun will inevitably die in about 5 billion years. When it's almost run out of hydrogen to fuse it will expand into a red giant, becoming so large it will take out the Earth. There's a good video demonstrating this here: http://science.howstuffworks.com/life/evolution/life-on-earth-end1.htm

You could add geomagnetic reversal and gamma ray bursts to your list. Also see: http://science.howstuffworks.com/life/evolution/life-on-earth-end1.htm