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Old September 9th, 2009 #3
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Earth based telescopes, and the Hubble too, have mechanics (and gyroscopes) that keep the lenses pointes in one precise location for the duration of the exposure. In this regard, a telescope is like a big clock with the hands ticking backward. The backward motion must account for the forward motion of the earth’s rotation and in the case of Hubble, its orbital velocity.

http://science.howstuffworks.com/hubble6.htm