To the left because directions are swapped when one is moving. Name several types of electromagnetic radiation from celestial objects that do not reach the Earth's surface. He was left handed and preferred the mirror image. Mirrors avoid the problem of chromatic aberration. Mirrors were easier to fabricate than lenses during Newton's time.
Mirrors collect light better than lenses.
In the same way as in optical telescopes. X-rays must bounce off the mirror at a very flat angle. Instead of using a concave mirror a convex mirror is used. Mirrors cannot be used in X-ray telescopes at all. Through a telescope it is seen to consist of millions of stars.