DULUTH – If you’ve never witnessed an occultation before, you’re in for a treat. Skywatchers across much of North America (except the southeast and parts of the east coast) on Wednesday evening will see the full moon slowly encroach on the planet Mars, then the engulf. From some locations, Mars will disappear for more than an hour behind the Moon.
An occultation is a bit like a conjunction, when the moon and the planet (or two planets) line up. But in an occultation, the alignment is so close to perfection that the nearest object covers the other – like hitting the bullseye.
Contribution / Stellarium with additions by Bob King
Lunar occultations of stars occur regularly. Stars suddenly fade out because despite their enormous size, they are so far away that they appear as mere bright dots even at high magnification. The hard edge of the moon approaches and quickly covers the stellar pip. At 4,212 miles wide (6,780 km), Mars is about twice as large as the Moon, but being about 50.6 million miles (814 million km) away, it looks tiny in comparison — 107 times smaller!
But his record is still much bigger than a star, so it will take several seconds for the moon to cover it. Seen from the Duluth, Minnesota area, the moon takes its first bite at 9:06 p.m. CST and completes the planet 43 seconds later. Watching Mars disappear will be a lot of fun to see up close in a telescope or even a pair of binoculars.
Contribution / Stellarium
What I’m really interested in is how far we’ll see Mars get to the moon with the naked eye before it disappears in the moonlight. When the two rise together on Wednesday evening, they will be close but easy to separate, about 1-2 degrees apart. That alone should sound incredible – I mean you have a full moon plus Mars at its brightest, and they’re side by side. Have your phone ready to snap a photo of the pair with a nice foreground, maybe something holiday-related like a lighted tree.
So watch out. The moon is moving east in its orbit (to the left in the northern hemisphere) and will slowly weave its way across the planet, closing the gap between them. At one point, you will almost see them touching each other. This should happen around 10-10:30 PM EST; 9-9:30 p.m. CST; 7-7:30 p.m. MST and 6-6:30 p.m. PST.
Contributed / Occult 4.9
The full moon is super bright, but so is Mars, now at magnitude -1.8 and brighter than Sirius, so I guess we’ll be able to see the planet right up to the edge of the moon without optical aid. But honestly, I don’t know, so I’d like to hear what you see. Please share your observations on my Astro Bob’s Astronomy for Everyone Facebook page.
Contribution / Stellarium
The path of the Moon on Mars varies depending on your location. From some places it is covered for only a few minutes, in others more than an hour. After the planet disappears, it will reappear minutes to over an hour later. the opposite side of the moon as if coming out of its edge. You don’t want to miss that either!
For your city’s vanish and respawn times, check out the International Occultation Timing Association’s (IOTA) page for the event. The times indicated are expressed in hours, minutes and seconds of universal time (UT). To convert UT to EST, subtract 5 hours from the times shown; 6 hours for CST; 7 hours for MST and 8 hours for PST. For example, if you live in Chicago, Mars will disappear at 3:10:58 UT. Subtract 6 hours and you get 9:10:58 p.m. on December 7.
For a better world map than the one included here, please see my recent Sky & Telescope article on the subject.
Contribution / Stellarium
Even if you don’t see the occultation, you will be in an awesome conjunction. The moon passes extremely close to Mars from many US cities. From Philadelphia, they will be just 1/30 lunar diameter at 10:51 p.m. EST and just as close as seen from Boston at 11:01 p.m. If clouds block the view, Italian astronomer Gianluca Masi will broadcast the event by direct. on its Virtual Telescope site starting at 10 p.m. CST (4 UT) on December 7.
According to meteorologist and astronomy enthusiast Joe Rao, favorable occultations of Mars occur for a specific location on average once every 14 years. The next one for North America will be on January 14, 2025.
Remember that you can enjoy occultation in any way – with the naked eye, with binoculars or a telescope. For close-up photography, use a telephoto lens with your camera mounted on a tripod. Start with ISO 400, a lens setting of f/8 and an exposure of around 1/500 to 1/2000 of a second. Inspect the images on the camera’s rear screen and if it’s not quite what you want, adjust the exposure accordingly. Good luck and enjoy!
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