Put a camera on a tripod and take a picture of the night sky. If the shutter speed is too long the stars begin to streak due to the rotation of the earth. A star tracker compensates for that rotation. A quality star tracker will extend your shutter speeds from seconds to several minutes so you can capture more detail in your night sky photos. A star tracker is the best way to do long exposures of the night sky without going to the time, trouble, learning curve, and high dollar expense of doing guided photography with a telescope.
