Watch the Moon Hide Mars

(Source: Sky and Telescope) The night of December 7–8 will be an exciting one for fans of the Red Planet. Not only will Mars be at opposition, but the full Moon will blot it out of the sky for many locations on Earth.**

On the night of December 7–8, Mars will be at opposition — opposite the Sun’s position in the sky. On that date, Earth is situated directly between Mars and the Sun. The planet is at its brightest, rising as the Sun sets and setting as the Sun rises. Opposition and closest approach to Earth, however, are offset by several days due to the relative shape and orientation of each planet’s orbit. Mars and Earth were closest on the night of November 30–December 1 when they were separated by 81.5 million kilometers (50.6 million miles). 

But that’s not all. On opposition night, viewers across large swaths of the globe will see the full Moon glide in front of Mars, in what is known as an occultation. Much of North America, northern Mexico, most of Europe, and northern Africa will be privy to this spectacle, provided skies are clear, of course. For North America, the occultation takes place in the convenient evening hours of December 7th. “If you’re outside this occultation zone, don’t despair,” says Diana Hannikainen, Observing Editor at Sky & Telescope. “The sight of the Red Planet skimming below the lunar disk will be an unforgettable experience nevertheless.”

Mars oppositions occur at roughly 26-month intervals, when Earth catches up to the Red Planet as they circle the Sun. The most recent opposition was in October 2020 and the next one will be in January 2025. The next time North America will be treated to the sight of Mars disappearing behind the Moon will be on the evening of January 13, 2025, two days before opposition. 

How and When to Watch Mars Disappear Behind the Moon

The Moon will be easy to find on the evening of December 7th. Just step outside, face east, and you’ll see it gleaming in Taurus. Depending on your location, Mars will be left or lower left of the bright lunar disk. That evening, the Red Planet will shine at magnitude –1.8, even brighter than Sirius, the brightest star in the night sky.

As the occultation begins, the Moon will be traveling leftward in the sky toward Mars. Because Mars presents a disk, albeit a small one, it will take the Moon many seconds, even as much as a minute, to gobble up the planet, depending on your viewing location. This is different than when the Moon eclipses distant, pinpoint stars, which disappear in an instant. The length of time that the Moon hides the Red Planet is again location dependent — for some viewers Mars will only be missing from the sky for a matter of minutes, others won’t see the planet for more than an hour. 

At the conclusion of the event, Mars re-emerges on the righthand side of the lunar disk, as the Moon moves away from the Red Planet. Even if you miss the beginning of the event, it’s still worth trying to catch the reappearance of Mars. 

Binoculars will come in handy to follow Mars as it slips behind the lunar disk on one side and reappears on the other —or, if you’re outside the occultation zone, to see it brush past the lower edge of the Moon. A telescope will be even better; if you don’t have access to one yourself, you can check if a nearby astronomy club is hosting a viewing party. Look for one near you in Sky & Telescope’s club listings.

Here’s a selection of disappearance and reappearance times for select North American cities: 

Here are times for when Mars is closest to the Moon outside the occultation zone:

For a more comprehensive list of locations, head over to the International Occultation Timing Association’s page dedicated to the event. 

Source: Sky and Telescope Press Release