The Moon, like the Earth, is not a perfect ball, its poles are slightly closer to the center than the equator. Scientists have determined which ellipsoid of rotation corresponds more to the shape of our moon. This data is important for creating a global positional system that will work on it.

## What is the shape of the Moon?

In a few years, NASA will begin to build a satellite infrastructure around the Moon, which will provide not only data transmission between spacecraft and stations but also the functioning of a global navigation system similar to GPS. At the same time, the engineers developing it have not yet taken into account the fact that our moon, like the Earth, is not a perfect ball.

At least, two researchers from the Eötvös Loránd University pay attention to this fact. The shape that the Earth has is called a geoid. It is quite complex and hard to describe. Of the simple figures, it is the closest to the sphere.

However, spacecraft and GPS satellites consider the shape of our planet not a sphere or a geoid, but an equivalent ellipsoid of rotation. This is a body, any section of which passing through the axis of rotation is an ellipse. In the case of the Earth, it is considered that it is flattened at the poles by 21 km.

## How to create an ellipsoid of rotation?

Something similar happens with the Moon. Only it rotates slower than the Earth, so the difference between its polar and equatorial radius is only 0.5 km. However, until now, no one has tried to create an equivalent ellipsoid of rotation for our moon. More precisely, Soviet scientists tried to do this back in the 1960s, but then they simply did not have enough accurate information to do it.

In the new study, the scientists used a database of the available surface, called the lunar selenoid (by analogy with the geoid), from which they took a sample of the height at evenly spaced points and found the major and minor semi-axes of the ellipsoid of rotation. By evenly increasing the number of sampling points from 100 to 100,000, the values of the two characteristics stabilized at 10,000 points.

Thus, they obtained a certain statistical sample of real surface marks and an ellipsoid of rotation with which they could be compared, and to say that the deviations are small enough to use this model in practice.

According to phys.org

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