A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances.
The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?

Solution

Radius of the lunar orbit is the distance between the earth and the moon.
Laser beam takes 2.56 second to reflect back, therefore distance of the moon from the earth is given by,
$straight d space equals space 1 half space ct space space space space equals space 1 half cross times 3 cross times 10 to the power of 8 cross times 2.56 space straight m space space space equals space 3.84 space cross times 10 to the power of 8 space straight m$