Monday’s full moon over Wyoming won’t be just full, it will appear huge in the night sky, a rare time when the first full moon of August is also a blue supermoon.
The first full moon in August is also called a sturgeon or mountain shadows moon, and Monday will be the first of four consecutive supermoons to close out 2024.
Supermoons happen when "the moon is within 90% of its closest approach to Earth," according to NASA. When that happens, the moon can appear up to 30% brighter and 14% larger than usual given their position in the sky, usually close to the horizon.
Monday’s is also the first and only full moon of August, so how can a supermoon also be a blue moon?
The short answer is calendar quirks. The long answer is a bit more complicated and less colorful.
Once In A Blue Moon (Times Two)
There are technically two types of blue moons. The better-known is the second full moon in one month, according to the Gregorian calendar.
But there are also seasonal blue moons, and the third of four full moons in a single season is a blue moon. The Aug. 19 supermoon is the third full moon of summer 2024, making it a seasonal blue moon. And because it’s the first full moon of August it’s a sturgeon moon (named for the fish). And also it’s within 90% of the closest it’ll get to Earth, making it a supermoon.
If that's confusing, join the club. Even Max Gilbraith, the planetarium coordinator for the University of Wyoming, wasn't familiar with the concept of a seasonal blue moon.
"I've never really encountered it," he said. "But this will be the third full moon of an astronomical season that has four full moons. I don't know why it's just the third moon is the blue moon, but I'm sure that there's some reason for it."
Despite the occurrence of four full moons in one season, only the third moon is the blue moon. The fourth full moon isn't anything noteworthy, although it will be another supermoon in September.
Calendar Quirks
Gilbraith wasn't familiar with a seasonal blue moon because it's a chronological phenomenon rather than an astronomical one.
"There are meteorological seasons and astronomical seasons," he said. "Meteorological seasons are adjusted for latitude and climate, whereas astronomical seasons are determined by the equinox or solstice."
Lunar calendars could be as old as civilization itself, with archaeological evidence suggesting that humans used the moon as a time-measuring tool as far back as 30,000 years ago.
Julius Caesar was the progenitor of the modern solar calendar, developing it in 46 B.C. It was used for 1,600 years until Pope Gregory XIII modified it in 1582, creating the Gregorian calendar used worldwide today.
Gilbraith said the quirks of the Gregorian calendar are good for blue moons. The calendar's blue moons have nothing to do with the astronomical aspects of the moon.
"It doesn't create any physical phenomena that you can observe," he said. "It's just a timekeeping sort of happenstance. It might be fun for superstitious reasons, but it's just an artifact of timekeeping."
Cool Moon
Ironically, "once in a blue moon" isn't as special as the idiom would suggest. Nevertheless, there are some fun facts about the upcoming sturgeon moon.
NASA said August's full moon will be so super that it should appear full for three days between Sunday night and Wednesday morning.
Furthermore, it's a rare super blue moon, which only happens every 10 to 20 years.
While the next seasonal blue moon will occur in May 2027, the next super blue moon will not occur until January 2037. So, put that on your Gregorian calendar.
For the record, "once in a blue moon" averages out to once every two or three years. That's slightly more frequent than a leap day, one of the important quirks of the Julian calendar that endured into the Gregorian calendar.
The Minute Summer Stops
According to his astronomical calendar, Gilbraith said that Wyoming's summer will officially end in the early hours of Sept. 22.
"Our terminal equinox is at 6:43 a.m. Mountain Time on Sept. 22," he said. "That is the official end of summer for everyone in Wyoming to the minute, so no tree leaves are allowed to come down until then."
The final full moon of this summer's seasonal blue moons will rise Sept. 17, putting it within the final days of the season. So, Wyomingites should savor this summer's sturgeon super blue moon while they can.
And no, the moon won't literally be blue when it rises Monday.
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
