### Video Transcript

What is the period of the orbit of a geostationary satellite?

Now to answer this question, we first need to understand what a geostationary satellite is. So if we start by imagining that this is the Earth, and let’s say this here is a geostationary satellite, then the thing that makes this satellite geostationary is that it always stays at the same position above the Earth’s surface. In other words then, as the Earth rotates, the satellite always remains above the same point on the surface. And that’s what makes the satellite geostationary, “geo” meaning Earth and “stationary” meaning not moving.

Now in reality, the satellite as we’ve already seen is moving. But it’s not moving in relation to Earth surface. It is constantly about the exact same point on Earth’s surface. And in order for it to do this, it must have an orbital period that’s the same as the period of Earth’s rotation. In other words, as the Earth completes one rotation, so does the geostationary satellite. And this is the only way for this satellite to remain geostationary, in other words, to remain above the same point on the surface of the Earth.

So now, we can recall that the time taken for Earth to complete one rotation is 24 hours because it takes a day for the Earth to go around once. And it’s worth noting by the way that this is a rotation about its axis. We’re not talking about the time taken by the Earth to go around the sun once. That period is one year. Like we said though in this particular case, we only care about the time taken for the Earth to rotate about its own axis once. And that period like we said earlier is one day or 24 hours. And therefore, the geostationary satellite must have the same period of orbit. And, hence, we have our answer. The period of the orbit of a geostationary satellite is 24 hours.