Saturday 9 August 2014

The August 2014 'Supermoon'.

At 5.44 pm GMT on Sunday 10 August 2014 the Moon will be at its closest point to the Earth in 2014, at a distance of 356 896 km. 27 minutes later it will officially be full (completely illuminated when seen from Earth), which means the two events will be virtually indistinguishable to human observers, something that has bee dubbed the 'Supermoon' by the popular press. The Moon completes one orbit about the Earth every 27.5 days, and like most orbiting bodies, its orbit is not completely circular, but slightly elliptical, so that the distance between the two bodies varies by about 3% over the course of a month. This elliptical orbit is also not completely regular, it periodically elongates then returns to normal, making some perigees closer than others. These cycles mean that the Moon will reached its furthest point from the Earth (apogee) of the year in the same lunar cycle, 406 568 km at 3.28 am GMT on Monday 28 July.

Simplified diagram of the Moon's orbit. NASA.

Although this is the closest point to the Earth that the Moon will reach in 2014, it is not exceptional. The Moon reached 356 577 km from the Earth on 2 August 2011, and will reach 356 876 on 28 September 2015. 

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