Starry night shots

[Hawaii Five-O]

I was wondering how those starry night shots are made, where the trees are in focus, but the stars are blurred to show movement?

 

[prodigy2k7]

A few minutes to 45 minute exposures... (Shutter Speed)..
Focus often set to infinity

 

[Garbz]

http://www.thephotoforum.com/forum/showthread.php?t=132957&highlight=star+trails look here for some info on how to do this without ruining your picture.