Getting a Precise Distance to the Moon

Using a laser beam and a handful of reflectors left behind by Apollo astronauts, a University of Washington astronomer is planning to find out how far away the moon really is. The center of the moon is roughly 238,700 miles from the center of the Earth. Measurements in the early ‘70s were only precise to within 10 inches. Current technology has trimmed the margin of error to less than an inch, but that’s not good enough for astronomer Tom Murphy. He plans within about a year to attach a laser to a 3.5-meter telescope at Apache Point, N.M., and send “bullets” of light to prism-like reflectors on the moon. The technique should reveal the moon’s distance to within 1 millimeter--about the thickness of a paper clip.

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Compiled by Times science writer Usha Lee McFarling