The best-known definition of a blue moon is to have two full moons in a calendar month - the second of which is called a blue moon. The third of the four full moons is called the blue moon. These don't occur as often as two full moons in a month. May 18 will be the third full moon of the season and the blue moon.
This year, the Vernal Equinox occurred at 5:58p EDT (2158 GMT) on 20 March followed less than 4 hours later by a full moon, officially the 1st full moon of Spring. The Blue Moon is also referred to as flower moon after the flowers that bloom in the month of May. Seasonal blue moons occur on average every 2.68 years.
As indicated by EarthSky astronomers, the last regular blue moon was on May 21, 2016.
We believe Blue Moons got their name from the Old English word belewe, meaning both "blue" and "to betray".
May only has one full moon, and that falls on Saturday the 18th.
The date of a full moon doesn't affect the full moon's color. We'll keep a few clouds around throughout the night, but there should be plenty of breaks in the clouds to see the full moon.
I'm all for an exciting "blood moon" (aka: a total lunar eclipse) or even a just slightly interesting "supermoon" when the full moon looks a smidge bigger in the sky, but there is absolutely no reason to get excited about this Saturday's "blue moon".
When is May's Blue Moon?
Despite its name and numerous pictures that show up when you search it, a Blue Moon rarely actually appears blue in the sky-but that's not to say it never does, Space.com writes.
In recent years, traditional Native American names for the full moons have become more common in modern day parlance.
The moon can also appear blue after a volcanic eruption or a major forest fire, as both instances will fair the air with ash and dust.
In Maryland and Washington, DC, for example, the ISS will be visible at about 9:27 p.m. on Saturday, and will look "similar to an airplane crossing the sky", the Post said.