The Moon snuggles close to the bright star Spica late tonight. They climb into good view by about midnight, and are high in the sky at dawn. At their closest, they’ll be separated by just a couple of degrees – about the width of your finger held at arm’s length.

That closeness is just an illusion – the Moon and the star are separated by a vast gulf.

The Moon is our closest neighbor. Tonight, it’s a little less than a quarter of a million miles away. At that distance, sunlight reflecting from the lunar surface takes about one and a third seconds to reach Earth. That means we see the Moon as it looked one and a third seconds earlier.

The Moon is moving farther from us – by an inch and a half per year. That’s a result of the tides. Earth and Moon exert a gravitational grip on each other. That slows Earth’s rotation, making the days a little longer. To balance the books, the Moon moves farther away.

Spica is more than nine billion times farther than the Moon. Its light takes about 250 years to reach Earth – the star is 250 light-years away. So as you look at Spica tonight, you’re actually seeing the bright star as it looked 250 years ago – about the time of the American Revolution.

And it’s moving away as well – by about 60 million miles per year. That’s a result of Spica’s motion around the center of the galaxy – an orbit that’s carrying the brightest star of Virgo into the distance.

Script by Damond Benningfield