Image Credit & Copyright: An old Moon shot of mine that I’ve butchered trying to make blue.
PUBLIC SERVICE ANNOUNCEMENT: Coming up this month; Friday, July 31, 2015 at 10:43 UTC (06:43 EDT) is a “Calendar” Blue moon! But what exactly is that you ask? Let’s have a look as there are three kinds!
NOTE: When an event happens on a certain date, it’s important to check the actual time of the event because remember, a calendar day is a period of daylight sandwiched between two periods of darkness. Thus, the event might not take place that night at all but instead in the morning before sunrise. In this particular case, the full moon is technically at 06:43 am eastern daylight time so all morning before sunrise will be the best time to witness the “Blue Moon.”
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 almost three years ago (August 31, 2012) and the next few of this type will take place on:
July 31, 2015
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 Grandfathers 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…..
NOTE: Ever notice when the Sun and Moon are low on the horizon they are yellow, orange or even red? Well the opposite effect is in play with an actual Blue moon. When planetary objects are low on the horizon, say, 30 degrees in elevation or lower, they are further away from you and that allows only a few select colors of light to reach your eyes. This also means that you are looking through about twice the atmosphere at that elevation vs. when they are overhead or near zenith. Atmosphere contains aerosols that are much smaller than 1 micron in diameter and those particles scatter blue light, letting the red show through. So don’t be surprised when your Blue Moon rises and it’s more red with a transition to orange, yellow and white more than any other color, especially blue!
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.