Here's something that happens once in a blue moon. A blue moon !

The standard bearer of rare events occurs again Aug. 31, its first appearance since March 2010 and its last 'til July 2015. Just what is a blue moon? Nothing terribly significant, actually; it's simply a second full moon in a single month. Full moons appear every 29 days due to the regularity of the lunar orbit. Overlaying our nonuniform yearly calendar onto this cycle causes the rare, and totally arbitrary, blue-moon-two-moon coincidence.

More lackluster lunar news: Blue moons aren’t actually blue, either. Nobody's even sure where that azure appellation came from. Or what the blue moon may portend as they are considered good luck to some, very bad luck to others. Either way, it seems appropriate that the memorial for recently deceased Neil Armstrong , the moon’s first human visitor, will be on the same day.

So Friday night, be sure you grab a brew, pop on an old Elvis ballad , toast Armstrong, and enjoy this lunar rarity!

Video by Paca Thomas.