Image credit & copyright: Me.
When the Full Moon rises tomorrow, Saturday, May 21, 2016 we will see the last seasonal blue moon until May of 2019. There are a few different definitions of Blue Moon and I’ve detailed them below but I have to be up front with you, I’m not too happy about this one because the big bright full moon will be pretty close to Mars which will be at opposition this weekend as well. It may be a pretty cool sight to see but for us observers who plan to check out Mars at its best and brightest, good ole Luna could be problematic.
Type 1: Two (2) Full Moons that occur in a single calendar month are called “CALENDAR” Blue Moons. They tend to occur on average every 2.7 years-ish and this is today’s “modern” definition of the event. The last one was last year, (July 31, 2015) and the next few of this type will take place on:
January 31, 2018
March 31, 2018
October 31, 2020
Type 2: These oddballs are called “SEASONAL” Blue Moons but I like to call em your Grandfather’s Blue Moons as they are the old school, original definition of the event. The standard was, that a Blue Moon was any season that had 4 full moons….the 3rd of which was considered a Blue Moon. Seasons by calendar are defined as the time periods between SOLSTICES and EQUINOXES or vice versa. The last one was on August 21, 2013 (3rd of 4 full moons of summer) and the next Blue moons of this sort will fall on:
May 21, 2016
May 18, 2019
August 22, 2021
Type 3: The final type of Blue Moon is an actual BLUE MOON…..but you’re going to need some tools; preferably an active volcano, massive amounts of ash and an atmosphere to deploy it into. For years volcanic eruptions have been associated with blue colored Moons; why? Most volcanic ash is about 1micron wide which just happens to be the length of a wavelength of red light. Thus, the red light is scattered and the blue shows through. Massive fires also have the ability to do this as well. Ever notice something looking bluish (Forest fires, grill smoke etc.) as you view it through smoke? There you go…..
Keep in mind that none of this is actually relevant to our day to day lives, actual astronomy or anything else. It’s just orbital mechanics wrestling with our man-made calendar system and on occasion it delivers to us an oddity that we can have some fun with. As far as popular culture is concerned; like the “Super Moons, Black Moons etc.” just embrace it and enjoy seeing something unusual even though we pretty much created it. Like anything else similar in nature to this; if it gets people to look up when they otherwise wouldn’t, I’m all for it.