On Wednesday the moment will come that is regarded as the start of spring, and less than four hours afterward, in a fairly rare coincidence, will come a full moon.

According to the Space.com website, it is the closest together in time for the two events since 1981.

Making matters even more unusual, this full moon, according to NASA, is considered a supermoon. A supermoon is a term used to describe the occurrence of a full moon at or near the time when the moon makes its closest approach to Earth on a given lunar orbit.

The coincidence of a full moon and a relatively close approach makes the moon seem a little bit bigger and a little bit brighter.

The spring equinox occurs at 5:58 p.m. on Wednesday. It is the moment when the sun is directly over the equator, and day and night are equal (or nearly equal) in duration. It is the moment that is commonly accepted as the start of spring.

Then, at 9:43 p.m. about three and three quarters of an hour afterward comes another noteworthy celestial event. The moon will be full.

By an appeal to instinctive understanding of probability theory, it can not be often that a full moon appears on the day of the spring equinox.

The date of the full moon may wander over the 31 days of March, but the equinox can occur on any of only three days. The likelihood of a full moon occurring on the same day as the equinox is thus relatively small.

Whether it occurs on the day of the equinox or note, this will be known as the worm moon.

Each of the full moons over the calendar year carries a name that generally arises from folklore, culture and tradition.

This month’s full moon has several names. But one of the most used is the worm moon. It is associated with the season of spring, a time for the earth to thaw and permit the emergency from their underground haunts of earthworms.

On its current orbit, the moon makes its closest approach to earth on Tuesday. According to the Time and Date website, it will occur about one day and six hours before the moon becomes full on Wednesday night. That appears to be close enough for the March full moon to be dubbed a supermoon.

So between them, Tuesday and Wednesday will provide a closest approach, an equinox, and a full moon. The worm moon.