This month's full Moon takes place on the June 23rd and it will be a "Mega Moon" or "Super Moon" - a dramatic combination of a full Moon when it's at or near perigee (closest point to Earth). As a result, the apparent size of the full Moon from our perspective appears larger than average.

The reason why such events are possible is because the Moon's orbit around the Earth is not circular and hence the separation between the two bodies is constantly changing. The distance between the Moon and the Earth at the extreme perigees (closest) and apogees (farthest) varies from around 356,400 km (221,460 miles) to 406,700 km (252,710 miles). This corresponds to a maximum and minimum apparent size of the Moon as seen from Earth of 33.5 and 29.4 arc minutes respectively.

At full Moon this month, the Moon is separated from the Earth by only 356,991 km (221,820 miles). It's located in the southern ecliptic constellation of Sagittarius and hence from mid-latitude northern hemisphere locations, the Moon rises after sunset, late in the evening and never climbs particular high about the horizon. From mid-latitude southern hemisphere locations, the situation is reversed. It's now winter and the Moon rises early in the evening and climbs very high in the night sky.

A good time to look for the Moon is just after sunset towards the eastern horizon when the well known "Moon illusion" is best seen. To the eye the Moon appears noticeably larger in size when it is hovers just above the horizon, compared to when it's much higher in the sky. Now at this time the effect is especially enhanced as it occurs during a Mega Moon. It's a curious illusion, but that's all it is. If you were to take a photograph of the Moon low down and then compared it with another photo of the Moon later, when it's higher in the sky, the size would be unchanged.