There was no full Moon in February of 2018, but March makes up for that with two. The first — the full Worm Moon (named for the seasonal return of earthworms to the grounds of North America) — occurred on March 1. The second (a blue moon) is on March 31.
It's relatively rare for a month to have two full moons — hence the saying, "once in a blue moon" — though it also happened in January, when the second full moon was an epic Super Blue Blood Moon.
As it happens, however, this will be the last blue moon of 2018. And there won't be another until 2020.
What Is a Blue Moon?
The second full moon in one calendar month is popularly called a blue moon. Astronomers, however, have a slightly different definition of a blue moon. Instead, they consider a blue moon the third full moon of a season that has four full moons.
Stargazers should note that blue moons don't actually appear blue in hue. Instead, a blue moon will appear on the eastern horizon in a glorious muted orange color as the sun sets. It's a gorgeous sight that happens every 29 days.
When Is the next Blue Moon?
An astronomer using that 'seasonal' blue moon explanation will tell you that the next one is on May 18, 2019. But if you opt for the modern day definition of two full moons in one month, the next blue moon isn't until October 31, 2020.
Does the Blue Moon Have any Significance?
A Blue Moon has no astronomical significance, but some religions do still use lunar months to determine the dates of religious festivals. The date of the Christian religion’s Easter celebration is held on the Sunday following the first full moon after the Spring Equinox. This year, the equinox occurs on Tuesday, March 20. So in this case, Easter's date is determined by the blue moon on March 31.
Does the Blue Moon Have Any Other Names?
North Americans tend to use the names for full moons first used by either Native Americans or early colonial Americans to help keep track of time and seasons. But they are specific only to the month they occur.
While the preceding full Worm Moon occurred on March 1, the next full moon after the blue moon is the Pink Moon on April 30.
The Old Farmer’s Almanac explains that the name Pink Moon comes from the appearance of the first spring flowers, though April's moon is also known as the Sprouting Grass Moon, the Egg Moon, and the Fish Moon.
So despite being a blue moon, the full moon on March 31 has no other name.