Why does a star form when i take a pic of a light at night ?

Question: Why does a star form when i take a pic of a light at night !?

i am taking pictures at night with my canon rebel xti and when i look at a light in the picture the light as a star around it!. is this normal !?
is there any way to get rid of it !?
is my lens dirty !? any way to clean it !?Www@QuestionHome@Com

Best Answer - Chosen by Asker:

It's normal!. It's the diffraction of light through the aperture blades!. The exact pattern of the star will depend on how many blades are in your lens' aperture!. You can change the points with a cross-screen filter!. They have them in patterns of 4 or 6 points!. Cokin even makes them that you can turn and change the angles between points!.

Cleaning your lens is easy!. Just get one of those micro-fiber cloths that's safe for use on fine optics, and wipe gently in a circular motion!. If it was the lens giving you problems, you'd notice streaks instead of stars!.

To reduce the effect of the star, use a wider aperture!.Www@QuestionHome@Com

Terisu answered it perfectly!. Personally, I prefer this look, and almost always shoot my night pics with a small aperture to 'star' the lights!.Www@QuestionHome@Com