Hubble.......

[R1Geezer]

I was reading about the hubble and it apparently it can lock on to a "target" and then not deviate by more than 7 one thousanths of an arc second. The equevalent of the thickness of a human hair at 1 mile. It needs to do this to achieve the long exposures for the amazing pictures it takes. Anyone any idea how it stays pointing in the same direction so accurately whilst orbiting the earth at 15000mph and at the same time orbiting the sun at 60000mph, not to mention orbiting the galaxy.!

[mibn2cweus]

Dont look now but the Sun is streaking across the sky at about 25000000mph. For reals. It's just way out there.
It's like when riding the train nearby trees and buildings wizz by but distant objects just sit there.

Also since Hubble has a constant momentum it only needs to compensate for any small change in the direction and optical axis of its target,

http://hubblesite.org/the_telescope/nuts_.and._bolts/instruments/fgs/