Bulgy Earth keeps sky from falling

摘要

Satellites stay in their orbits thanks to Earth's squashed shape -something we've only just discovered. Our planet is ringed by more than a thousand working satellites, and for the most part they stay up there quite happily. But it is only now that we understand why. Ideally, a tiny satellite orbiting a perfectly spherical planet will remain there forever, assuming nothing nearby disturbs it. But Earth is not a perfect sphere, and many things can disturb its low-orbiting satellites - first and foremost, the moon. According to the laws of motion, the moon's influence alone should cause satellites to crash into the atmosphere and burn up.