MadSci Network: Astronomy |
Dear Rosa, Our moon, the International Space Station, Mir and all the satellites are falling! Our earth has very strong gravity and just as you are pulled right down to earth when you jump off a swing, the satellites are being pulled down equally hard. However, they have been pushed to speeds of 18,000 miles per hour or more, so as they fall, they miss the earth. That's hard to imagine, so here's how Isaac Newton explained it in the 17th century. Imagine throwing a baseball as far as you can. It curves down and finally bounces on the ground because our gravity pulls it down. Now load a cannon ball in a really huge cannon and FIRE! The projectile flies a long ways, but gravity pulls it down and it eventually curves down and smashes into the ground. Our space program, NASA, uses powerful rockets to push satellites so fast that they fall past the horizon, all the way around the earth! If space was a perfect vacuum, satellites would orbit forever. However, even 300 miles up where the Hubble Space Telescope and shuttles operate, there are a few molecules of air which eventually slow down a satellite. If the satellites aren't sped back up with thrusters or by the shuttle, they eventually fall back to earth. Unlike all our artificial satellites, the moon is moving away from us and slowing down our rotation at the same time. But that's another question for the MADSCIENTIST! Thank you for writing and keep an eye on the sky. You can often see satellites moving among the stars. Jim Foerch James C. Veen Observatory Lowell, Michigan, USA, Earth
Try the links in the MadSci Library for more information on Astronomy.