What is the distance between the Earth and the Moon?

Average Earth-Moon distance: 384,000 Km

The average distance between the two stars is 384,000 km. For those who may have difficulty visualizing what this interval really represents (especially at this scale), line up 30 planets the size of the Earth next to each other. This is the Earth-Moon distance.

Common people mistakenly believe that the distance between the Earth and the Moon is the same at any time of year. No! It varies according to the position of the Moon in its orbit. We are not talking about a variation of a few tens of kilometers but more than 49,000 km (49,090 km to be precise) between the minimum and maximum Earth-Moon distance. More than the Earth’s perimeter! This precision in measuring the lunar distance was made possible by light. LIDAR (light detection and ranging) stations installed on the Earth’s surface since May 1962 make it possible to analyse the totality of a light beam emitted by retro-reflectors installed on the Moon.

Minimum (perigee) and maximum (apogee) distance between the Earth and the Moon

Did you know that every year the Moon moves a little further away from the Earth? According to the same LIDAR measurement system, the two stars are moving away an average of 3.8 cm per year due to the interaction of the tides between the Earth and the Moon. Simply put, the Moon’s gravity exerts a drag on the Earth that slows down its rotation, and conversely the Earth’s gravity exerts a pull on the Moon that widens its orbit.

Location of lunar reflectors on the surface of the Moon reflecting the laser beam from observatories located on the Earth (see image below)

Observatories for measuring the Earth-Moon distance using a laser beam (LLR)

Goddard Geophysical and Astronomical Observatory capable of accurately calculating the Earth-Moon distance / NASA Credit

Well, don’t tell me, 3.8 cm / year is a drop of water in a 384,000 km long ocean that separates the Earth from the Moon. According to a NASA study conducted in 1999 by two eminent scientists, Bruce G. Bills and Richard D. Ray, this speed of separation is “abnormally high”. This would suggest that the Moon’s age is not 4 billion years, as most scientists believe, but “only” 1.5 billion years. The Earth-Moon distance would therefore continue to increase until the rotations of the two stars “synchronize”. Such a process could take 50 billion years according to current models. Unfortunately, we will not be around to see this, unless Google finds the recipe to give us eternal life ;).

N.B.: If you want to play with the Moon, NASA offers a 3D visualization of the star. Enjoy 🙂