How to Watch the Moon Photobombing Mars on On December 7: "A Rare and Wonderful Astronomical Event"

You have to be in the right place at the right time to see it.

A rare celestial event will occur on Dec. 7, when the moon will pass directly in front of Mars, blocking its light from view. NASA is calling it "one of those magical moments when the sky changes dramatically before your very eyes." It's called an occultation, a spooky-sounding term derived from the Latin word meaning "hidden." Occultations happen once or twice a year somewhere on the planet. But this one is exceptionally rare.

"This doesn't happen very often. In fact, in 25 years of viewing, I've never seen a lunar occultation of Mars," said Dean Regas, astronomer for the Cincinnati Observatory. And you have to be in the right place at the right time to see it. Where and when is that? Read on to find out.

1
Occultations Explained

NASA

"The moon passes in front of planets in the night sky several times per year," says NASA. "In fact, it generally occults Mars itself at least a couple of times per year. But each occultation is visible from only a small portion of Earth's surface, so it's not super common for any particular spot on Earth to see them frequently."

The agency says stars will just blink out when the moon passes in front of them. "But planets are not just points of light like stars — they appear as circular little disks, so planets actually take several seconds to disappear and later reemerge," it says. "So if you're in the viewing zone, enjoy this relatively rare opportunity to watch a bright planet being occulted by the moon."

2
What the Occultation Will Look Like

NASA

"When you look toward the moon that night at 10:20, you will see this very bright orange-colored star – which is actually Mars – just below the full moon," Regas told the Cincinnati Inquirer. "One second it will be there, and the next, poof, it will be gone."

"Mars' light will be blocked (or occulted) by the much closer moon," he added. "For about 30 minutes, Mars will be behind the moon but will pop back into view as quickly as it was snuffed out."

3
The Timeline

NASA

Regas breaks down how the lunar occultation will proceed (all times are Eastern standard time):

  • 10:15-10:20 p.m.: Mars will look like a reddish bump of light on the bottom left portion of the moon
  • 10:21 p.m.: Mars starts moving behind the moon, then will disappear in about one second
  • 10:52 p.m.: Mars emerges from behind the moon's bottom right 

4
Where You Can See It

NASA

You'll be able to view the lunar occultation with the naked eye, although a telescope or binoculars can help. It will be visible in parts of North America, Europe, and Northern Africa. Viewers in the Southeast and on the East Coast will see the Moon just graze past Mars, NASA says.

A skywatching app can provide a precise time for your area, although experts recommend that you begin watching 20 minutes before the scheduled event to ensure you don't miss anything. 

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5
More Stargazing This Month

NASA

If you can't get enough stargazing, this month you can get a good view of Pegasus, the constellation named after the winged horse of Greek mythology. It's one of the largest of the 88 constellations visible in the night sky. Its most prominent feature is a pattern of stars called the Great Square, which form the center of the horse's body.

This December, Pegasus is exceptionally visible. NASA recommends facing southward to find Jupiter about halfway up the sky. The Great Square will be visible beginning about 15 degrees to the north.

Michael Martin
Michael Martin is a New York City-based writer and editor. Read more
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