What is the peristerum?

What is lost when the sun fuses hydrogen to helium? Who are the first three man go to moon? What is the definition of the moon phases? First manned space station April 19 1971? Is space traveling safe? Does the moon control the gravity? What astronomer described earth as the center of universe? What is the second most common element in stars? Where does the solor power come from? What does the connection and interaction between the sun and earth do? What is a piece of rock or metal from space that enters the earths atmosphere at high speed? When using a microscope Why should we start with the lens in the lowest position and then move up? Which two shuttles never went to space? How did astronauts prepare for the Apollo 11 mission? Why a green cap looks black in blue light? What happens when the Doomsday Clock strikes Midnight? What is the fastest rotating body in the solar system? Why is it called waxing after the new moon? Why is the camel in Giotto adoration of the Magi not exactly realistic? What is question mark shaped star called?