Zenith, the point in the heavens that is directly above the head of the observer. The opposite point, that directly below the observer's feet, is the nadir. Zenith also applies to the highest point a heavenly body appears to reach above the horizon. The sun reaches its zenith at noon.
A black hole occurs when a massive star dies -- its enormous mass implodes and becomes so heavy that it bends space. So how do astronomers detect something that they can't see?
The man immortalized on the left was behind the three laws of motion and the universal law of gravitation. He was also competitive, temperamental and fascinated with alchemy. How well do you know Newton?