You might think that the Moon would pass in front of planets quite often, but in fact this is quite a rare event, and one which amateur astronomers are keen to watch and photograph. The disappearance of one astronomical body behind another is known as an occultation. Such an event occurs on Wednesday 18 December 2024, as seen from the UK and western Europe.
However, the occultation will take place during daylight in mid-morning, and will be quite low in the north-north west, so this will be a challenging observation. Normally, finding Mars in the daytime sky is extremely difficult. But to make things a bit easier, the nearby Moon will be just three days after full, so it will be quite bright and easier to spot.
Being daytime, Mars will be even harder to see against the bright sky, and it’s unlikely that just ordinary binoculars will show it. But at the moment Mars is close to Earth so it is brighter than usual, and if the sky is very clear it should be visible and photographable using a telescope with a magnification of 50 or more.
The exact timing of the event depends on where you are, but from the UK it begins between 09:15 and 09:30 GMT with Mars disappearing behind the bright limb of the Moon, taking about 15 seconds to do so. It emerges from the dark limb of the Moon some 50 minutes or so later.
Locating the Moon will itself be a challenge. Even typical GoTo telescopes will not be able to find it, as they need to be set up using stars. The easiest means will be to use a sky app on a device with accurate accelerometers that will indicate the correct part of the sky. As a guide, from central England the Moon will be at an azimuth of 290° (west-north-west) and an elevation of 12° at the start of the occultation.
Simulations of the location of Mars around the Moon as seen from the UK are shown below.
The reappearance as seen from the UK will be at the dark limb near Mare Crisium. Simulation from Stellarium software.