How did Kepler arrive at his laws? If one already knows the distances to the planets (and the eccentricity of the orbits etc.) it is understandable how one might proceed to establish the second and ...
The black hole at the center of the Milky Way is believed to have erupted as an active galactic nucleus approximately 2 million years ago, at which time it would have been visible to early humans. How ...
Trying to observe the night sky for a few weeks, the motion of the Sun and the stars pretty much fits into the Geocentric Theory i.e. All of them move around the Earth. What then, which particular ...