The light you see through the telescope, just like the light you see with naked eyes, has been traveling a long time to reach us. So you're seeing the way some star was in the past. Even without a telescope some light from that star would reach you eye, just not enough to trigger the sort of signal to which your brain responds. The large initial lens or mirror of the telescope gathers more light than does the smaller pupil of your eye.
Mike W.
(published on 03/24/2018)
