Moons of May

1 May with a beautiful waning crescent moon

Moon Phases for May 2019. … The four main Moon phases in order are the New Moon, First Quarter Moon, Full Moon and Last Quarter Moon. … These interim phases are Waxing Crescent Moon, Waxing Gibbous Moon, Waning Gibbous Moon and Waning Crescent Moon https://www.moongiant.com/calendar/

How Rare Is a Blue Moon?

May 2019’s Flower Moon is a Blue Moon

The term once in a Blue Moon suggests something happens very rarely. So, how often do Blue Moons occur? The answer depends on how you define a Blue Moon.

https://www.timeanddate.com/astronomy/moon/blue-moon.html

here are two ways of calculating the date of a Blue Moon.

Seasonal Blue Moon = The third Full Moon in an astronomical season with four Full Moons (versus the usual three).
Monthly Blue Moon = The second Full Moon in a month with two Full Moons.

In the 1100 years between 1550 and 2650, there are 408 seasonal Blue Moons and 456 monthly Blue Moons. This means that either Blue Moon occurs roughly every two or three years, although the monthly ones are a little more frequent than the seasonal ones.

The seasonal Blue Moon is the original astronomical definition of a Blue Moon. Usually, there are three Full Moons between each astronomical season, which is the time between each solstice and equinox. But some years, there are four Full Moons in a season. When this happens, the third Full Moon is called a Blue Moon.

In 2019, May’s Full Moon is a seasonal Blue Moon. The astronomical season started with the equinox on March 20, and the first Full Moon alignment was less than four hours later; on March 21. The second Full Moon was on April 19, and the third, the Blue Moon, is on May 18. The fourth and last Full Moon before the June solstice is on June 17.

A Moon that actually looks blue, however, is a very rare sight. The Moon, full or any other phase, can appear blue when the atmosphere is filled with dust or smoke particles of a certain size: slightly wider than 900 nm. The particles scatter the red light, making the Moon appear blue. This is known as Mie scattering and can happen for instance after a dust storm, a forest fire, or a volcanic eruption.

Eruptions like the ones on Mt. Krakatoa in Indonesia (1883), El Chichon in Mexico (1983), on Mt. St. Helens in the US (1980), and Mount Pinatubo in the Philippines (1991) are all known to have made the moon look blue. Some people even suggest the term once in a Blue Moon is based on these rare occasions, rather than the Full Moon definitions above.