FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

Moving Forward, Forever Falling

This week sees the anniversaries of some rocket-related events - the first successful flight of a German A-4 missile, the launch of the first satellite, Sputnik, and the birth of the father of modern rocketry, Robert Goddard. So what better time to talk about the fundamental, but rarely understood phenomenon of sending something into orbit. 

How do we do it? How on earth do those things stay up there? Are they suddenly weightless? Is there no gravity up there to yank them down to the ground? Put on your thinking caps!

You may have seen a space launch, either from Vandenberg up north or a Shuttle launch, or one of the Apollo missions from days gone by. Did you notice that when they were launched they didn't head straight up? They all started rolling over at an angle right away. If you could follow them long enough you'd notice that they eventually fly a path parallel with the surface of the earth. That's the secret. Let me explain.

Isaac Newton, in his attempt to explain what being in orbit was all about, used an example of a cannon firing a cannonball from a mountaintop. Let me use a football instead, since it is the season. When we throw a football straight out in front of us, gravity causes it to take a curved path to the ground. If we throw it with more force, the football goes farther in its curved path until it eventually hits the ground. So far, no problem.

But what if we could throw that sucker out with a lot of force, I mean a lot. It would go really far, wouldn't it? Actually farther than you think. Since the surface of the earth is curved, your football gets to travel a bit farther down the way than expected. Throw it harder and it may travel part way around the earth before it hits the ground. Throw it harder still and it may never hit the curved surface of our planet. It will just continue going round and round the planet. That is being in orbit.

Is there still gravity? Yes! Gravity is bending its path, causing it to fall, but that curved planet isn't allowing the poor football to hit the ground. 

Get something to travel fast enough - over 17000 mph near Earth's surface - but also parallel to that surface, and the object "falls" forever with the planet continuously curving away from the falling object. (Of course, we are assuming air resistance is playing no role in slowing it down.)

Those satellites you see sometimes in the evening, the Shuttles, the Space Station, the Moon itself, are all falling to Earth. But their forward motion prevents them from crashing into it. 

Did this all give your head a good spin? Good! Until next time, clear skies!
Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me