How is the Distance to the Moon Measured?

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The speed of light is known very accurately and is 299,792 kilometers per second. If a beam of light is aimed towards Moon and then reflected back, the distance from the Earth to the Moon can be worked out. For this, a large telescope is required.
The mirror of the telescope is used as a searchlight's reflector to transmit light pulses towards special reflecting panels stationed by astronauts on Moon.

It takes 2 1/2 minutes to complete the total journey. The Moon's distance is then calculated. It is 384,000 km from the Earth.

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