The Supermoon approaches

The so-called ‘Supermoon’, or the full perigee Moon to use its more scientifically accurate name, will be visible across the world today and tomorrow. The Supermoon event is caused by the Moon reaching its perigee – the point in its orbit where it is closest to the Earth.

As with all space related things, the word “close” here is used relatively to talk about when the Moon is a mere 363,400km away from Earth as opposed to its normal distance of 405,500km. The latter is enough distance to fit every planet in the solar system between the Moon and Earth if they were placed end to end. 

The differing distance is due to the Moon’s orbit being elliptical which means that sometimes it is further away than others. Astronomers describe the Moon as having an ‘eccentricity’ of 0.55, compared to a perfect circle which has an ‘eccentricity’ of zero. It is simply good timing that the perigee and the full Moon are happening at the same time and we get to see a Moon which looks 7% larger and 15% brighter than normal. This is such a rare coincidence that it has not happened since the 16th January 1948 and it won’t be this close again until the 25th November 2034.

There has been a lot of sensationalist media coverage hyping people up for a Moon which will appear up to 30% brighter than usual but this is misleading. The ‘Supermoon’ will only appear 30% brighter than its opposite state, when the Moon is furthest away from Earth at its apogee.
In addition to this ‘Supermoon’, Mars and Venus are beginning their climb towards each other and eventual convergence early in 2017. Until then, these two planets will gradually grow closer and closer in the night sky. The clear winter skies are always good for planet spotting and astronomers are eagerly anticipating two rare events in close succession.