A supermoon occurs when the moon is at perigee - the point in its orbit that brings it closest to Earth - and in its fullest phase.

The perigee between the Earth and the moon can vary by as much as the diameter of the Earth during any given month.

In fact, its elliptical orbit sees its distance vary from 363,104 kilometres at perigee to 405,696 kilometres at apogee.

The sun's gravity is actually responsible for pulling the Earth and moon into a closer alignment, causing the orbital variation.

For residents the moon appeared brighter and larger in the horizon of the night sky, but that is no more than an optical illusion.

An explanation for its apparent size is that the moon appears much bigger on the horizon because we have trees and buildings to compare it to.

When it is located much higher in the sky, we have nothing to compare it to but the sky itself.

A supermoon generally occurs once a year and is viewable in both the Northern and Southern hemispheres.

Luckily for those who missed the weekend's event, other supermoons will occur in August and September. The one on August 10 will be the biggest of the year, as the moon will be closest to Earth on that day.

Supermoons will appear smaller in the distant future because the moon is slowly propelling itself out of Earth's orbit, moving 3.8 centimetres further from Earth each year.

Scientists suspect that at formation, the moon started out about 22,530 kilometres from the planet, but now, it's about about 384,402 kilometres away.