Twice in a Blue Moon
SALT LAKE CITY, UTAH – July 31, 2015 (Gephardt Daily) – It’s one thing to happen “once in a blue moon,” but how about twice?
Those looking skyward spotted the unusual phenomenon last night, and the blue moon is supposed to be back this evening.
The July 31 appearance of the month’s second full moon will be the first such occurrence in the Americas since August 2012. Every month has a full moon, but because the lunar cycle and the calendar year aren’t perfectly synched, about every three years we end up with two in the same calendar month.
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 0.7 micron. The particles scatter the red light making the Moon appear blue in color, this can happen for instance after a dust storm, forest fire or a volcanic eruption.
Eruptions like on Mt. Krakatoa, Indonesia (1883), El Chichon, Mexico (1983), Mt. St. Helens (1980) and Mount Pinatubo (1991) are all known to have caused blue moons.
So when the phrase “once in a blue moon” was coined, it meant something so rare you’d be lucky (or unlucky) to see in your lifetime, according to NASA’s National Space Science Data Center.
The most recent blue moon that was truly blue in hue was in Edinburgh, Scotland, in September 1950.
This lunar event will not be seen again until January 2018.
