How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies?
Just to think about this is mind boggling. But how do scientist get these numbers? What technology/system/theory do they they use?
Pluto is no longer a member of the planets in the solar system. Why was it disqualified as a planet? What is the criteria for classifying an Astronomical Object as a Planet? Does this criteria ...