This month, we get another rare planetary occultation when the Moon will move in front of the planet Mars.
The best time to see the lunar occultation of Mars will be the morning of 18 December 2024 at 09:05–10:25 UT
Yes, the lunar occultation of Mars occurs during the morning, with the catch (there’s always one!) that the Sun will be up.
Get more info with our guide on how to observe Mars and how to calculate and observe lunar occultations.
Mars occultation observing tips and times
Mars will be at mag. –0.9 at the time of the 18 December lunar occultation.
The Moon will be at a large and bright phase, appearing as an 89%-lit waning gibbous, so it should be pretty easy to locate in a clear sky.
Look for it in plenty of time before the start of the event, above the west-northwest horizon.
Once you’ve located the Moon, you’ll need a bit of help, as at mag. –0.9 Mars will be too dim to be seen with just your eyes.
Binoculars should work fine for the lunar occultation of Mars, although a small telescope on a driven mount will make life a lot easier.
Needless to say, a large telescope will fare best of all, but we’d recommend keeping the magnification low to medium.
Go too high and the already low contrast of the daytime sky will result in a poor image, with Mars hard to see well.
As the Moon is fairly close to Earth, your position on Earth’s surface, even to a few tens of kilometres, will affect the apparent position of the Moon relative to Mars in the sky.
As a consequence, it’s not possible to give one universal start time for the occultation; rather, we’ve provided a guide time as seen from the centre of the UK.
To make sure you don’t miss the event, we’d recommend starting to observe at least 15–20 minutes before the stated times.
What you'll see
As it’s the waning gibbous Moon that will be doing the occulting, it’ll be the bright leading edge of the Moon that first covers Mars.
The planet will have an apparent diameter of 13 arcseconds on 18 December and as a result its disappearance will take 22 seconds.
It will take a similar time to reappear from behind the Moon’s dark limb.
The daylight nature of the sky will mean the dark, night portion of the Moon’s surface will not be visible at all, making spotting the re-emerging planet that bit harder.
We’d recommend a lower power which covers a reasonable size of the Moon’s edge if you’re uncertain where to look.
This should give you the best chance of seeing the planet’s reappearance.
If you observe or photograph the lunar occultation of Mars on 18 December, send us your observations and images by emailing contactus@skyatnightmagazine.com.
This article appeared in the December 2024 issue of BBC Sky at Night Magazine.
