7/17/2003: Earth's artificial satellites
 

http://cellar.org/2003/sats.gif

A few days ago the Astronomy pic of the Day featured this in an animated GIF which showed all the satellites and then zeroed in on the International Space Station. I just pulled out one frame of the animation because I find it so fascinating.

It turns out that there are two common locations for satellites: low earth orbit just out of range of the atmosphere, and geostationary orbit, where the satellite stays over the same point on the equator. So the outer ring there is made up of the geostationary satellites which revolve around the earth at the same speed as the earth.

The color code:

blue = weather satellites
yellow = communication satellites
green = scientific satellites
cyan = navigation satellites
black = secret military satellites
not indicated = georgia satellites

black = secret military satellites
Heh, now that's funny. Especially on that black background. :D

The background is actually white.

:eek:

Georgia?
 

Who knew that Georgia Tech could do that?

Next thing you know, old Jed's a millionaire....

Dave, look again with your good eye. :D

Did you miss the joke?

i must admit, it took me an embarassingly long time to get it.

~james

Since the gif background is black and the Cellar background is grey, yes, I missed it.:confused:

Yes, the two most common are LEO (low earth orbit) and GEO (geosynchronous earth orbit).

There are many other orbits, however. The GPS constellation orbits at MEO - mid earth orbit. The black spy satellites in some cases have very odd-shaped orbits designed to swing them low over the surface and then head way out again.

So that explains the scatter?

(Secret military satellites are represented by black dots. The joke was the implication that there are so many of them represented in that image that you can't see the background.)

The fun one is called Molniya. Its tilted like 60 degrees from the equator and elliptical. Kinda difficult to launch geo from latitudes far from the equator (takes too much fuel). That and another problem with Geostationary is even at that distance from the earth, the poles look real flattened and nothing very north or south gets a good signal (alot of Russia, Sweden, Finland, etc).

as for the spy satellites, they are likely highly elliptical. They swoop down close (travelling much faster than when they are far away). The benefit is that even though people may THINK they know when it will pass, the satellite could technically make a small burn at the apogee and offset the time of overpass (would still be daylight though).

oh and if you dont know much about the GEO, the ring is a highly sought after place to be. so an international body (forget the name now) allocates the ring into sections. the sections are then taken by a different governing body (like the FCC) and their only rule is don't interfere with the next section over. So you can put as many satellites in that space as you want and use frequency bands as allocated.