The Moon is the nearest object to Earth in the Universe – an average of 238,900 miles (384,400km) away. Its distance varies slightly because it follows an egg-shaped (elliptical) orbit around the Earth.
When the Apollo astronauts visited the Moon, from 1969 to 1972, they left behind small ‘retro’reflectors’, rather like the reflectors on the back of a car. Astronomers on Earth shoot a powerful pulse of laser light at these retro-reflectors, and about two and a half seconds later their telescopes pick up a faint flash as the pulse of light returns to Earth. They then multiply the time it takes for the pulse to leave Earth and return, by the speed of the light, and divide the result by two to arrive at the Moon’s distance from Earth.
The Moon and the Earth are drawing apart because the friction between the Earth’s ocean floor and the water heaped up in the tides is gradually slowing its rotation. This is making it lose energy. In return, the bulges of the Earth’s ocean tides pull the Moon forward in its orbit, making it gain energy. The Moon is therefore gradually moving away from the Earth as it is pulled into a larger orbit.
Picture Credit : Google
