Forty years ago today, as Apollo 11 reached the halfway point to the Moon, Mission Control asked the crew to look back at Earth.
MISSION CONTROL: We've got a laser -- it's a blue-green laser -- that we're gonna flash on and off. It's coming out of McDonald Observatory near El Paso... We're going to activate that momentarily. Would you please take a look through the telescope and see if you can see it, over.... APOLLO 11: Okay, Charlie.
They were preparing for an important experiment -- one that's still going on today.
When they landed on the Moon a few days later, astronauts Neil Armstrong and Buzz Aldrin set up a special reflector -- one that would bounce a laser beam back in the direction it came from. Scientists at McDonald and elsewhere would measure the time it took the laser beam to make the round trip, and from that, determine the distance to the Moon within a few inches.
The experiment was designed to test Albert Einstein's theory of gravity -- to find out whether the force of gravity changes over time. It would also reveal details about the Moon's interior, Earth's rotation, and the drift of Earth's continents.
Two other Apollo crews also left laser reflectors on the Moon. And today, scientists still "shoot the Moon" -- continuing Apollo's last experiment.
Look for the Moon in the east at first light. Venus, the brilliant "morning star," is well below it. Orange Mars is a little to the right of the Moon, with the orange star Aldebaran to the right of Venus.
Script by Damond Benningfield, Copyright 2009
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