How many satellites orbit the Earth? At what rate do they orbit the earth?
I was looking at a full moon the other night with my telescope and noticed a black dot move across the moon quite rapidly. This happened a few times and others who were with me were able to confirm.
There is no way the ISS would make its orbit around the Earth that quickly for us to be able to see it a few times. Therefore there must have been others. How many are there, and how long does the average satellite take to make a full orbit around the earth?
This seems like it belongs over on [Space.SE], but it's honestly too broad. There are *lots* of satellites, and they have all kinds of different orbits.
I suspect this is a joke question. Although artificial satellites do transit our one natural satellite, there would not be several of them in a few minutes, and they certainly wouldn't show anywhere near the level of detail in the Photoshop'd image above.
We didn't see them in the detail as above but we definitely saw a similar (obviously more blurry) shape about 3 or 4 times within a few minutes. Being as there are thousands of satellites in orbit around the Earth, this shouldn't be so unbelievable. @barrycarter
I'm pretty sure the above image is NOT faked by the way - there are several enthusiasts out there who photograph International Space Station passes of the moon, or even of the sun with appropriate protection. There are quite a few such images on the web.
@barrycarter The photo shows an Earth-orbiting satellite transiting the moon. It does not show a moon-orbiting satellite.
I think the question is a little broad as pointed out by other users. There are all kinds of satellites--tracked and non-tracked--in Earth orbit and that is constantly changing. Maybe you could focus your question on what types of satellites would be visible (with an amateur telescope) transiting the moon. The accepted answer does a good job addressing this.
@gerrit Yes, I understand this, but that satellite seems huge in terms of angular size. The moon is about 30 minutes in diameter, making this satellite about 30 seconds in diameter. I'm pretty sure satellites are much smaller than this as viewed from Earth. Of course, I could be wrong, but the sizes seem off to me.
There are over 1000 operational satellites, and probably as many again defunct or non-operational satellites in orbit, plus a great deal more small pieces of space junk.
About half of these are in a low earth orbit (LEO). Satellites in LEO have a period of between 90 minutes and 130 minutes. But you would not expect a satellite to follow the same path in the sky in two orbits, as the earth will have moved between orbits of the satellite. So it is very unlikely that you will see the same satellite pass in front of the moon twice.
Satellites in LEO are moving fast! They will cross the moon's disc in less than a second, and transits are rare, as each is a path only 7km wide. at any one time, a transit is visible from less than 100th of 1% of the Earth's surface. To obtain the awesome photo that you have linked, the astrophotographer would have had to use some orbital prediction software to calculate the exact time of a solar transit by the ISS and travel to a carefully calculated position (and prayed for clear skies). You could be observing the moon all year and never see a transit.
Most of the remaining satellites are in Geostationary orbits, They orbit at a great distance over the equator. As their orbital period is exactly one day, they appear to hang in space above a point on the Earth. Such satellites are too distant to be seen as "dots".