News Equipment Observatory Astrophotography Projects About me
The following image was taken using a Canon EOS350D, 55mm lense, with a shutter speed of 776 seconds.

It clearly shows the earth's rotation. In Paintshop Pro I measured the angle the stars traveled.

Now we can simply calculate how much time it takes to rotate a full 360 degrees:

3.2 degrees in 776 seconds, means

(360/3.2) * 776 seconds = 87300 seconds = 1455 minutes = 24 hours and 15 minutes.

Obviously, it should have been 24 hours, but I couldn't measure the angle beyond one decimal. Calculating backwards, I should have measured 3.23 degrees instead of 3.2, but this accuracy is quite satisfactory.