With all the media hype about this evenings ‘Supermoon’ what is actually happening? Well, first thing to consider is what is actually happening to the moon? The short answer is nothing! The moon is doing what it always does, orbiting the Earth. It’s orbit is not circular rather it orbits the planet in an elliptical fashion. This occurs due to the Earth and Moon sharing a common centre of gravity called the barycentre which lies approximately 2600km from the Earth’s centre. As both orbit around the barycentre resulting in the moon’s elliptical orbit resulting in a close approach called perigee and when it’s furthest away its called apogee. This occurs every month as the moon continuously orbits the Earth. To complicate matters the moon’s orbit is also inclined the Earth’s plane by approximately 5.14°. Tonight’s ‘Supermoon’ is a coincidence of the moon’s closet approach (perigee) and being in it’s full phase. The correct terminology for this event is perigee-syzygy.
The actual term ‘Supermoon’ is not astronomical but rather originated as a modern astrological term. However, there is some interesting research that looks at the link between the association of oceanic and crystal tides leading to the claim that earthquakes and volcanic eruptions may be linked to the phenomenon, but there is little evidence to support these occurrences.