So the sun has just set, and the stars begin to shine, and suddenly you see a moving star in the sky.

Is it a plane? no its too far away and not flashing.

Is it a shooing star? well its much too slow?

so what is it?

Well in all likelihood its a satellite, and if you are lucky you might just be spotting the international space station.

Types of satellites

There are two types main types of satellites

1. Geostationary satellites - These are used by large telecommunications companies, and they orbit about 30,000km above the earth, so they circle the earth at exactly the same speed. This means they stay in the same part of the sky all the time (day and night) so these satellites are usually too far away to see, and they don't move in the sky.
2. LEO, and MEO - These satellites orbit the earth much closer to earth LEO means Low earth orbit, and MEO means medium earth orbit. These are the stars that are constantly moving in the sky, and are the ones you see just after dusk.

So interested in seeing these with your own eyes, there are apps and websites that track satellites, I use "heavens above" (I have no association with them). The app knows your location from your phone and can tell you where to look and when.

Why use LEO satellites

One last thing, you might ask, why would you have satellites in LEO that are constantly moving through the sky, why not just geostationary. Well there are lots of reasons, but I thought I would explore one reason. The main reason that Elon Musk's starlink network for internet service is using LEO, is that it is much closer to the earth, so the signals travel faster.

It might not seem much, but light travels 300,000km in a second, so for it to travel 60,000km to the geostationary satellite and back, that would take maybe 0.2 seconds. (i.e. 200ms). Now that's not a problem for watching Netflix, or YouTube, because it will buffer. But try playing a first person shooter game with a 200ms delay, and you will try to avoid an enemy by ducking or jumping and 0.2 seconds later it moves, unfortunately you are too late, and will lose the game.

Posted with STEMGeeks