The Moon “shines” by reflecting sunlight. But it’s not a great mirror – it reflects only about one-tenth of the sunlight that strikes it. So it’s actually quite dark.

Even so, it reflects enough radio waves that it served as the first communication satellite. In the late 1950s and early ’60s, the United States Navy used the Moon to relay signals between bases, and to some ships at sea.

That developed from an earlier project that listened for radar transmitted from inside the Soviet Union. Originally called Project Joe, it started in 1947, after the Army successfully bounced its own radar waves off the Moon. It began regular operations 75 years ago this month.

Early results were better than expected, so the Navy began studying how to use the Moon to send signals, not just receive them.

At the time, it maintained long-range contact by bouncing radio waves off the ionosphere – an electrically charged layer of the atmosphere. But storms on the Sun could interrupt transmissions. The Moon would be more reliable. In 1954, project leader James Trexler beamed his own voice to the Moon and back. And by late 1960, the system was in regular use – bouncing radio waves off the Moon.

The Moon is just past first quarter tonight, so the Sun lights up a bit more than half of the lunar disk. The bright star Antares is well to the upper left of the Moon. More about the Moon and Antares tomorrow.

Script by Damond Benningfield