To the best of our knowledge, astrologer Richard Nolle coined the term supermoonover 30 years ago. The term has only recently come into popular usage. Nolle has defined a supermoon as:
… a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit.
That’s a pretty generous definition and allows for many supermoons. By this definition, according to Nolle:
There are 4-6 supermoons a year on average.