Why do satellites orbit the earth in about 90 minutes while the stars take 24 hours?
A viewer asks why satellites orbit the earth roughly every 90 minutes while the stars take 24 hours, and how to explain that they do not orbit at the same rate.
Answer
Satellites go at different speeds for different reasons. Weather satellites go slowest, polar satellites go fast, and the ISS circles the earth about three times a day. Whatever thrust a satellite is given is the speed it attains, and it keeps that speed by conservation of momentum: once a body is put into motion, unless there is a net external force on it, it keeps going, which is inertia. So a satellite moving at, say, 2,000 miles an hour will go around the earth in about twelve hours. It depends entirely on the thrust given to the satellite, which is why satellites move at different speeds and are not tied to the daily rotation of the stars.