# What Is The Distance Between The Earth And The Moon

The moon is the only natural satellite of the earth. At the same time, it is the planetary satellite closest to the Sun, the fifth largest natural planetary satellite of the solar system and the second brightest (after the Sun) object in the earth's sky.

## The distance between the luminaries and its changes

The diameter of the Moon (3474 km) is slightly more than 1/4 the diameter of the Earth. Thus, the Moon has many times less mass and 6 times stronger gravity than the Earth. The force of mutual gravity between them makes the moon move in an orbit around the earth. The satellite completely orbits the planet in 27, 3 days.

The distance between the centers of the Moon and the Earth is 384 467 km, which is approximately equal to the sum of 30 Earth diameters. Every year, however, the Moon moves away from the planet by almost 4 cm. The reason for this is the constant decrease in the force of gravity between celestial bodies, which occurs due to the loss of energy in the Earth-Moon system.

Since the Moon is close to the Earth and has a rather large mass, there is a gravitational interaction between celestial bodies in the form of ebb and flow, which take place on the coast of the oceans, in various bodies of water and the earth's crust. Because of them, friction occurs between the bottom and the oceans, the mantle and the earth's crust, which causes the loss of kinetic energy in the Moon-Earth system. For the same reason, every 120 years, the Earth's day is lengthened by 0.001 seconds.

Taking into account the annual distance from the Earth of its satellite, it can be calculated that in a thousand years the Moon will move away from the planet by about 40 meters.

## Research in this area

People have tried to measure the distance from the Earth to the Moon since ancient times. Among them was, for example, the ancient Greek scholar Aristarchus of Samos. He was mistaken almost 20 times in his calculations, since the technologies of those times did not allow for high accuracy.

Scientists were able to measure the distance between the Earth and the Moon with minimal error using laser guns. There were also attempts to do this using photons of light reflected from the mirrors of the lunar rovers, but they ended in failure.

San Diego University physicist Tom Murphy wanted to measure distance to the nearest millimeter. Together with a team of colleagues, he sent laser pulses of 100 quadrillion photons to reflectors on the Moon. In the best case, only one of them came back, and often the telescope could not record even this. It is assumed that the reason for the failure is in the distorted trajectory along which the photons return. According to Tom Murphy, the reason for the negligible return signal is that the lunar dust covers the glass prisms of the reflectors.