Full, Blue and Super!

Credit: Victor Gutierrez from Click2pins

Tonight’s Full Moon already looks full and will for a couple of nights, but officially shows up full at 8:35pm! With our relatively dry air in place we will see a spectacular moon!

And not only is it a full moon but it’s also a super moon meaning in its orbit around the earth it’s closer than normal so looks even bigger and brighter. This is, in fact, the third of four super moons this year (the final being next month). But don’t expect this super full moon to actually be blue--that coinage comes from it simply being the second full moon in the same month (a definition created in 1946 by Sky & Telescope magazine). Earlier definitions called a blue moon the name for the third full Moon in a season that has four Moons, but nowadays we go with the current. I remember my mom always said “Once in a blue moon” referring to something rare and, sure enough, these two-in-one-month moons only show up about every couple of years.

And they aren’t really blue, although...back in 1883 an Indonesian volcano named Krakatoa exploded akin to a 100-megaton nuclear bomb. Plumes of ash rose to the very top of Earth’s atmosphere and the moon turned blue. You can read more on that event from NASA right here.

CREDIT: Mo Eid from pexels.com

So having a blue moon is a 2-3 year event but what about a SUPER blue moon, like ours tonight? Only about every 8 years on average. Our last one was in 2018 and the next one doesn’t happen until 2037! Astronomer Tony Rice is full of amazing information like that and he explains:

Supermoons happen when the 29.53059-day synodic month (full moon to full moon) lines sufficiently up with the 27.55455-day anomalistic month (perigee to perigee) to meet one of the five definitions. Because of wiggle room in those definitions (keep in mind that this is a term with roots in astrology, not astronomy), supermoons happen in groups of 3-4. For months other than February where the full moon falls on the 1st or early on the 2nd, the next moon happens 29.5 days later, within that calendar month, earning the “blue” label. So blue supermoons, or super blue moons, happen when these two regular cycles (synodic and anomalistic) and not-so-regular calendar months line up juuuuust right.

Tony admits that is probably more detail than you were looking for, but the bottom line is that tonight is only the 16th Super, Blue Full moon since 1900 and there will only be three more between now and 2050! Don’t take that for granted--get out and enjoy that moon!

If you would like to know more about Tony Rice and subscribe to his excellent emails you can go right here. If you are a Skywatcher, his information is a must!


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About the Author:

KPRC 2's chief meteorologist with four decades of experience forecasting Houston's weather.