THE BIG THREE

The top sights to observe or image this month

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Perigee full Moon and the 'Moon illusion'

BEST TIME TO SEE: Evenings of 14-16 June

The lunar orbit is elliptical and over time this means the distance between Earth and the Moon varies. As you would expect, the apparent diameter of the Moon varies over its orbit because of this distance change. Apogee describes when the Moon is furthest from Earth, perigee when nearest. When it's closest, the Moon's apparent size is around 34 arcminutes, while at apogee the Moon's apparent size is around 30 arcminutes.

Apogee and perigee have no connection with lunar phase, the orbit cycle being out of sync with the phase cycle. A full Moon near perigee gains more attention than a regular full Moon because it appears larger and brighter than average, and has also become known by the popular term 'supermoon'. However, if you compare a perigee full Moon to the ones in previous and following months you probably wouldn't notice any difference.

Last month, the Moon was full at 05:15 BST (04:15 UT) on 16 May. Lunar perigee occurred at 16:27 BST (15:27 UT) on the 17th, meaning that was a perigee full Moon. The Moon had an apparent diameter of over 33' 40" on that date. In June, full Moon occurs at 12:52 BST (11:52 UT) on 14 June, perigee at 00:23 BST (23:23 UT) on 15/14 June, the Moon's apparent diameter reaching 33' 56", fractionally larger than May's. July's full Moon occurs on 13 July at 19:38 BST (18:38 UT), perigee on the 13th at 10:05 BST (09:05 UT), resulting in a maximum apparent diameter of 33' 57".