Why won't my nikon d3100 focus when taking pictures of stars?

I've tried several time using diff setting trying to take pictures of the stars to try and get some star trails and the stupid camera won't focus and it says its "too dark", which clearly, duh, its at night of course its dark. I'm getting really frustrated… Any help? Anyone?

Set the exposure for a longer time?

Of course the camera won't autofocus. There's no contrast. It's just a dark sky with little bright specks everywhere.

long explanation short- you will have to manually focus.

Um yeah, the camera is not the stupid one.

A poor craftsman blames his tools. A poor photographer blames his camera.

Repeat this 100 times: "It isn't the camera its the photographer."

This site will help you with star trails: http://www.danheller.com/star-trails

You need to learn how to actually use your camera. A good place to begin is with the Owner's Manual. To accomplish your goal of making star trail pictures you need to know how to use your camera in Manual Mode. You'll also need a tripod and a locking remote release for exposures longer than 30 seconds. Turn AF and VR to "OFF".In other words you must be in control of the camera.

This site is also useful for setting low-light exposures:
http://www.calculator.org/...osure.aspx I used the Scene 'Distant view of city skyline or floodlit buildings' and ISO 200 for these pictures:
100mm lens @ f11, exposure of 30 seconds.
200mm lens @ f11, exposure of 30 seconds.

In my admittedly biased opinion I think they look pretty good - especially since the camera used was a 35 year old 35mm film camera.

"It isn't the camera its the photographer."

Except when making long exposures like my examples or shooting indoors with flash I use Aperture Priority. That's about the only thing I let the camera do for me - select a shutter speed based on the ISO and aperture I'm using. The main reason I use Aperture Priority is because I shoot a lot of landscapes and like to maximize my Depth of Field.

So learn to use your camera and take control of it. This site will really help you:
http://www.nikonusa.com/...index.html Who better than Nikon to teach you to use your Nikon D3100?