PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
Laser measurement of Earth-Moon distance. A laser beam fired from a telescope in France, used to measure the distance between the Earth and the Moon. A series of pulses, each 0.4 nanoseconds long, is fired at reflectors placed on the Moon during US Apollo and Russian 'Lunakhod' missions. The precise round-trip time of the pulse gives a distance measurement to an accuracy of 3cm. This technique, laser astrometry, gives very accurate data on the orbital dynamics of the Earth and Moon, and has implications for various Earth and Space sciences. Photographed at the Observatory of the Cote d'Azur near Grasse, southern France.
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