Fabio Bustamante wrote:
> This photo left me thinking...
> I suppose telescopes may request some considerably long exposures to
> shoot stars, galaxies, etc. They must need an extremely precise
> gyroscope system to stop all rotations and get an absolutely steady
Since the rotation of the earth is known, they either
use a fixed "clockwork" (normally a very precise worm wheel
and drive) or are "guided".
This is done by pointing a guide telescope (on the same mount
as the "real" telescope) at a nice bright star,
and using a feedback loop (on the scope drive) to keep the bright
This allows long exposures on stars (and other things) which are
not so bright.