MSTEP Science Practice Test

The main idea is telling apart how Earth moves in space and how long that movement takes. Earth spins on its axis, which gives us day and night; that daily spin is called rotation. The tilt refers to the angle of Earth's axis relative to its orbit, and it helps produce seasons. The motion that carries Earth around the Sun is a revolution – it describes the complete cycle as Earth returns to the same position in its orbit. The path Earth follows around the Sun is an orbit, but when we talk about the time it takes to go all the way around, we’re describing the orbital period, which is the revolution. Since this cycle takes about one year, the best term for the motion is revolution.