by Peggy Barnett

Created on: December 28, 2006   Last Updated: May 02, 2007

Reflections on the Moon Landing

"one small step""a giant leap for mankind"
- July 20, 1969, Apollo 11 moon landing

A Danish astronomer in 1675 named Olaus Roemer calculated the measurement of the speed of light by observing the amount of time required for one of Jupiter's moons to enter the shadow of that planet. The calculation occurred after Roemer had noticed a sixteen minute difference in time as to when this happened between the point at which the earth is farthest away from the planet Jupiter and the point at which the earth is closest to it. The speed of light, which is now known to be the distance a light wave travels in one second, is a basic concept used in measuring distances between various celestial bodies and the earth.

By the 1950's, astronomers understood that radio waves, a form of light wave, could be used to measure exact distances between remote objects in space and the earth. The technology, developed after World War II and which created the radio telescope, had also been used to calculate the distance between the earth and its nearest neighbor, the moon. Although the calculations as to the distances between celestial bodies and the earth appeared correct, astronomers desired to corroborate their findings by firmly establishing a single distance between the earth and another celestial object, providing them with a separate piece of objective data.

After a decade of unmanned and manned satellite launches, moon exploration began in 1969 with the Apollo 11 moon landing. Between 1969 and 1972, astronauts from the United States collected scientific information about the moon, including accurate maps. These early astronauts also placed a reflector on the moon to enable the first truly accurate measurement of the distance between the earth and the moon, by utilizing a concept of geometry known as triangulation.

According to Wikipedia, triangulation is the process of finding coordinates and distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other reference points, using the law of Sinas. Simply put, in order to accurately measure the distance to the reflector placed at a known location on the moon, three known transmitter locations (and the distances between them) would be required on earth. A light wave would then be directed from each transmitter location on earth towards the reflector on the moon, which would "bounce" these light waves back towards the points on earth. Since the speed of the particular light waves would be known, it would only be necessary to measure the interval of time that occurred between sending a "signal" towards the reflector and receiving it.

Based upon the placement of the reflector and the application of triangulation, the distance between the moon and the earth is currently measured to an accuracy of 5 centimeters, firmly establishing a given distance between the earth and another celestial object. By using this data as a corollary, astronomers have been able to make relative corrections to other distance data.

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