[Physics] Video of Earth spinning

earthrotation

If the Earth is spinning or rotating at a really fast speed, why haven't we seen any videos from space of it spinning when we get a lot of photos of it?

Best Answer

First of all, let's calculate the rotational velocity of the Earth, at the equator. The diameter of the earth is 12,756 km. Therefor, the speed is ${12,756km*\pi}/{24 hrs}=1669 km/hr$.

Given that we know the rate of spin of the Earth, what else would be required to see this change?

  1. The point of reference would need to be relative to the Sun, or possible the Earth-Sun system, but not LEO like most spacecraft are. Geosync. orbit would not work either, as the satellite is moving at the same speed as the Earth. A very high orbit might work, such as the Moon would be in.
  2. In order to achieve 1, a significant distance from the Earth is required.
  3. Given that a large distance is required, the Earth will not appear to be moving as quickly as it would otherwise.

Just to compare this, I pulled the speed of the moon orbiting the Earth from wikipedia. That speed is 1.022 km/s, or about 3,680 km/hr. That is a much higher speed than the Earth rotational speed. Given that the distance requirements are similar to see the rotational speed of the Earth, it seems that one would have to notice the moon orbiting if one could notice the rotation of the Earth, in real time. (Note, it's a bit easier to see the Earth rotating, due to the easy comparison, but...)