Like distance from the Earth. And do some of them “sit” in one place, like always over North America?
Orbits are circles or ovals, and the satellite must always be moving to stay in orbit. But the time to go around depends on the distance, so there is a distance where the satellite takes 24 hours to go around, which matches the Earth’s rotation, which is geosynchronous. A subset of these is called geostationary, when the orbit is a circle around the equator, so it stays in the same spot of the sky. (Then we can aim a ground antenna just once and don’t have to adjust it.) Satellites at this distance add 1/4 second delay to any signal because of light speed. This orbit is very tight, since it can not vary in altitude by more than a few hundred meters. (More than that would cause them to drift east or west out of the assigned spot.) There are a limited number of “slots” in this orbit to keep the satellites safely separated and to prevent their signals from overlapping. Most of these are used for communication, especially TV. A few are for weather, as they can watch an entire hemisphere constantly.
Other satellites operate in a lower orbit. Here the orbital period can be as low as 90 minutes. Most of these orbits are inclined so they pass over most of the earth instead of just the equator. The orbit (circle) stays in one angle while the earth rotates underneath. Satellites here get better images because they are closer to Earth, but take a day (or more) to see everything. They also have greatly reduced light speed delays. These orbits eventually decay because of tiny amounts of air at that altitude.
That’s crazy. TIL about geostationary satellites. I didn’t think a satellite could ‘stay still’ in space above an area and have wrongly told people it’s not possible. I have some comment edits to make.
Wait till you hear about legrange points. These are points where 2 massive object (like the sun and earth) create a sort of pocket where a satellite can orbit “nothing”. I have massively simplyfied it, off course.
Heard of them (UFOs sub, lots of heavy reading, skimming the physics parts) but never knew what they were. That’s a great understandable explanation, and fascinating, thanks.
The JWST actually sits at a Lagrange Point (L2)
There is a good write up including video and animations to explain what where and why https://webb.nasa.gov/content/about/orbit.html
My buddy does orbital mechanics or whatever for Amazon currently, he explained to me that satellites have tracks which are paths at different elevations and directions to ensure they don’t hit each other. One time he fucked up and the company’s satellite entered another’s track. He was beside himself thinking he was going to be responsible for the destruction of multimillion dollar satellites. Luckily they never hit and life went on.
