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 ?
Time taken by the laser beam to return to Earth after reflection from the Moon =2.56 s Speed of light =3×10 8 m/s Time taken by the laser beam to reach Moon =1/2×2.56=1.28 s Radius of the lunar orbit = Distance between the Earth and the Moon =1.28×3×10 8 =3.84×10 8 m =3.84×10 5 km
