Favourable circumstances for this month's full moon on 24/25 May result in the spectacular occurrence of a 'supermoon' or mega-Moon. If you can get to a site that has a reasonably flat south-eastern horizon then the rising moon will look unnaturally huge and spectacular!

This mega-Moon was imaged in 2011. Credit: Jamie Cooper
 
If seen against the backdrop of a distant town or city then all the better. This impression of the Moon being 'as big as a plate', as Astronomy Now's resident lunar expert Peter Grego puts it, is real and rooted in our perception of the shape of the sky as a flattened dome.

The Moon doesn't orbit the Earth in a perfect circle rather an ellipse, and when it's closest to Earth (perigee), it appears 14 percent larger and 30 percent brighter than when it's at its furthest (apogee). This month the Moon has an apparent diameter of slightly over 33 arcminutes at perigee (358,376km) on 26 May at 3.43am as opposed to 32.5 arcminutes at apogee (406,485km) on 9 June. Even allowing for it being perceptively larger this week, the mega-Moon is merely an illusion. Prepare to be thrilled by experiencing it for yourself as it rises after 8.30pm BST and has pulled clear of the horizon by 10pm.

Full moon occurs on 25 May at 5.25am and there is a penumbral eclipse of the Moon. Before you get too excited, this is not the spectacular total lunar eclipse, where our satellite is fully immersed into the Earth's deep umbral shadow and can turn a beautiful coppery-red. This time the Moon's southern edge barely enters the outer, much fainter, penumbral shadow just as it sets in the south-west. At most a very subtle darkening of the far southern edge will occur but even die-hard lunar aficionados will have difficultly seeing it. First contact is at 4.53am with the maximum extent at 5.11am and last contact at 5.27am.