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This Wednesday night, the full Moon will eclipse a very bright Mars [1]

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Date: 2022-12-02

On December 7-8, Mars will be at opposition, and the Moon will pass right in front of it. Time shown is Eastern

We’ll have a lovely spectacle in the sky this Wednesday night (Dec. 7), and a rather rare one at that. Over the course of about an hour, a very bright Mars will disappear behind the full Moon and reemerge on the other side. And you don’t even have to stay up late. Scientific American describes the rendezvous this way:

It takes about 30 to 45 seconds for the moon to cover Mars entirely, like slowly drawing a curtain across a window. By eye, the two will seem to kiss, and then Mars will fade from view in less than a minute.

This occultation of Mars by the Moon is an event that, for any given location on Earth, happens only about once every 14 years . But it’s very easy to observe — rural or urban — if you know when to go and look. After all, it’s not too hard to find a full Moon! We’ll check out event times for lots of locations across America below.

This particular occultation is especially cool because both the Moon and Mars will be at opposition, or directly opposite the Sun from Earth’s point of view, as you see in the main diary picture above. That’s not a big deal for the Moon, which is at opposition every time it’s full, but Mars is only at opposition about every 26 months . The upshot is that both bodies will be very bright.

Mars won’t be this bright for very long, though; Earth goes around the Sun faster than Mars, and as we pass up Mars in its orbit, it’ll fade from our point of view pretty quickly:

While Mars’ opposition is just after midnight on Dec. 8, its closest approach to Earth is on Dec. 1, because Mars’ and Earth’s orbits aren’t perfect concentric circles. But that’s splitting hairs.

It seems like Moon-Mars occultations would happen a lot because the Moon keeps going around and around Earth, and we can see Mars for much of the year. But they are relatively rare in practice, because compared to Earth’s orbit, the Moon’s orbit is tilted about 5° , and Mars’ orbit is tilted about 1.85° , and so things don’t usually line up quite right. The diagrams below are pretty obviously not to scale, but you get the idea:

The sizes of the celestial bodies are exaggerated for clarity

This is also why most full Moons aren’t lunar eclipses. When the Moon, Earth, and Sun line up every 27.322 days , the full Moon usually isn’t in Earth’s shadow, as in the above diagram. But about twice a year , it is, and we get a lunar eclipse.

To appreciate the real scale of Earth and Moon, and why even a 5° tilt will keep the Moon out of Earth’s shadow much of the time, here’s a quickie video that shows the real scale. It also shows the speed of light to scale for extra fun:

x YouTube Video

We won’t have a lunar eclipse for this particular event (which I guess would have been even awesomer), because Mars and the Moon will both be up out of Earth’s orbital plane a little. I used Dominic Ford’s terrific website in-the-sky.org to check on this, and you can see below that if we line up the Sun and Earth on Wednesday night, Mars is indeed a little out of line:

Super closeup of the Solar System on December 7, 2022. The Sun is the yellow thing behind Earth

Anyway, without further ado, let’s get to viewing times and places! The map below shows the region in which Mars will be completely obscured by the Moon:

All of America gets a show of one kind or another

But if you’re not within the purple zone, don’t despair! Those of us in Boston, Philadelphia, New York, Knoxville, Huntsville, etc. are just barely outside the purple zone, but that means we will get to see Mars skim just underneath the Moon, so we’ll be able to watch its progress the whole way.

Because Mars and the Moon are opposite the Sun, they’ll rise right at sunset, close to each other, and they’ll keep getting closer as they ascend, until they consummate the event. It’s an all-night spectacle. Below is a guide to how the climax will unfold, as seen from some representative cities:

Times and places

If you’re within the purple zone, you’ll be able to find a city even closer to you at this site , so you can estimate your times of Mars’ disappearance and reappearance (scroll down to “US”). But like I said, if you’re outside the purple zone, you’re good to go, too. Check out this table from Sky & Telescope to get the time and separation at closest approach:

In Boston, Philadelphia, New York, Knoxville, and Huntsville, the approach will be within one arcminute (1’)! The Moon appears 31’ wide , so that’s pretty dang close. What does that look like in practice? Well, you Easterners and Southerners will have to look up and find out Wednesday night!

If you’d like another read on this topic that focuses more on Mars observation, go to this article by the incomparable Bob King, whom you can always rely on for a compelling take on any astronomical topic.

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[1] Url: https://www.dailykos.com/stories/2022/12/2/2138928/-This-Wednesday-night-the-full-Moon-will-eclipse-a-very-bright-Mars

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