Throwback Thursday: Projecting Lasers Onto The Moon

Out of context, “shooting lasers at the moon” sounds closer to the nefarious plot of a Saturday morning cartoon villain than a milestone in the history of lasers. The process is known as lunar laser ranging, which is the process of using lasers to measure the distance between the earth and the moon.

In May of 1962, a team from Massachusetts Institute of Technology (MIT) were the first to successfully project the beam onto the surface of the moon, and have it reflect back. The beam was directed at Albategnius, a long-identified, larger-sized crater on the moon’s surface.

As part of the Apollo missions, reflectors were placed into the moon to assist in future measurements and tests. Since lasers were first used for lunar ranging, researchers have learned a great deal about the interactions between the Earth and the moon. Thanks to lunar laser ranging, we have learned that the moon is moving away from the Earth at a much greater rate than once imagined. (Approximately 3.8 centimeters per year.)

Despite these findings, researchers have determined that the gravitational pull between the two bodies is, in fact, stable, staying within the constraint of Newton’s gravitational constant. No one needs to worry about a disruption of the tides or variations in the Earth’s rotation any time soon.

Lunar laser ranging also confirmed that Einstein’s general theory of relativity can be used to predict the moon’s orbit almost as accurately as the lasers can. In a way, both methods prove that the other is within the same realm of accuracy.

The next step for researchers is to increase the accuracy of lunar laser ranging to the exact millimeter. However, these developments are slowed by the degradation of the reflectors. The laser pulses aimed toward the lunar surface are returning at a fractional rate to what was once standard. Some speculate that the beams are being interfered with by a coat of lunar dust over the reflectors.  It is unknown at this time if there are any future plans to fix reflectors, and push the limits of known Earth-to-moon measurements.

About the Author
Steven Glover is a proud member of the LIA staff. When he is not at work he is actively involved in several charitable efforts.
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