A supermoon is a full moon at the near end of the moon's elliptical orbit — up to 14% wider and 30% brighter than one at the far end.

The orbit's distance runs from about 356,000 to 407,000 kilometres. The nearest full moons of a year are the ones called super; the farthest are sometimes called micro. Sol draws each of the year's full moons at its apparent size, so the difference can be seen rather than believed.

The difference is real but slight to the eye; the moon looks biggest near the horizon for another reason, an illusion.