**One of our readers sent us the following question:**

*The earth really does not have the shape of a perfect sphere and is slightly flattened at the poles. The equatorial radius of the Earth is 6378.1 km, and the polar radius is 6356.8 km, the difference is only 21 km, which is negligible compared to the size of the planet: about 0.32%.*

*This difference is caused by the rotation of the Earth around its axis: the centrifugal force slightly stretches the planet near the equator, and as it approaches the poles, it decreases and completely disappears at the poles themselves.*

**If an observer looks at the Earth, for example, from the Moon, then he will see it perfectly round, our eye is simply not able to catch such a small difference between the polar and equatorial radii. You can verify this by looking at any photo of the Earth from space.**

**For the Moon, exactly the same laws apply, but the radius of the Moon is 3.5 times less than that of the Earth, and the speed of its rotation around its axis is approximately 100 times less than that of the Earth, thus, the centrifugal force acting on the equator of the Moon will be much less than on the ground.**

**As a result, the equatorial radius of the Moon is 1738.1 km, and the polar radius is 1736 km, the difference is only 2 km, i.e. 0.11% of the radius, which is less significant for the Moon than 21 km for the Earth. Therefore, if you look at the Moon with the naked eye, then it seems to us perfectly round, although of course, just like the Earth is not perfectly round.**