It appears that the Sun, Moon, and stars rise and set each day, when in reality it is the Earth that rotates. If you expose an image for a very long period of time, you can see the effects of the Earth's rotation as astronomical objects appear to move within the exposure. This fact makes photographing astronomical objects somewhat difficult. On the other hand, the star trailing effects can be rather cool.
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Taken from my front porch
Combination of 19 X ~1.5 minute exposures
Stacked using Image Stacker. Processed with Photoshop CS
Nikon D70 w/ 18-70mm lens
F/4.5
ISO 400
Focal Length of 18mm
Mouse over the image to see labels
Taken from my front porch
Combination of 8 X ~2.5 minute exposures
Stacked using Image Stacker. Processed with Photoshop CS
Nikon D70 w/ 18-70mm lens
F/4.5
ISO 800
Focal Length of 18mm