“It’s closest point is the perigee, which is an average distance of 226,000 miles – 363,300km – from Earth.
“When a Full Moon appears at perigee it is slightly brighter and larger than a regular Full Moon – and that’s where we get a ‘Supermoon’.”
According to the US space agency, the term Supermoon was coined in 1979.
A Supermoon is sometimes known as a Perigean Moon or Perigean Full Moon.
But not all Supermoons are equal and some appear closer than others.