Twice in a Blue Moon

2018_1_19 - Twice in a Blue Moon_Rose Focht.jpg

Our 6-year-old is fascinated by calendars. When we discovered his interest last year, we put him in charge of marking each day off the calendar, and he’s taken that responsibility very seriously. Every morning (almost), he starts off the day by crossing out the previous day, and usually provides a commentary about our progress through the week or month, or about upcoming events.

Changing over the calendar to a new year was an exciting development. This new calendar has some different features from the old one, and Lawrence, looking at the days ahead, excitedly announced, “Wow! Two full moons this month!” I checked his assessment and confirmed that yes, January 2018 does have a blue moon. What fun!

Truth be told, I sometimes wish I were more organized and proactive in our study of astronomy. Though I have a lot of ideas and good intentions, our actual observations of celestial phenomena, such as harvest moons and meteor showers, tend to be rather hit-or-miss. So it’s nice to have another source of reminders that you learn something new every day.

We discussed the linguistic, historical, and astronomical significance of a blue moon, which in modern parlance is commonly used to designate the second full moon that occurs in a single month. Apparently, the original term “Blue Moon” referred to an extra full moon that fell in a single season. Three full moons per season—or twelve per year—is generally the standard, and each full moon had its own designation (although these names tend to vary by culture and region: Harvest Moon in September was the most consistent term I found). When a season ended up with four full moons, the third was called a Blue Moon.

To make things even more interesting, the Blue Moon this January 31st will feature a total lunar eclipse, which hasn’t happened for 150 years. We won’t get to witness the full spectacle from our vantage point here on the East Coast of North America, but we should get to see a bit of the partial and penumbral phases. (If we remember to stay up and look out, that is. We knew about the Super-moon on January 1st but missed seeing that too, because we were still sleeping off New Year’s Eve.)

We didn’t have far to look to find another singularity: there will be another blue moon in March 2018! February this year has no full moon, but it’s sandwiched between two months with two full moons each. So under the old system, the only Blue Moon here would be the third one in the season, or the first one in March; whereas under the new system, the Blue Moon in March would be the one at the end of the month. It’s interesting to note that the new classification now gives us two nearly back-to-back Blue Moons instead of one (there’s inflation for you).

Twice in a Blue Moon - Rose Focht     Rose7

The phrase “Once in a blue moon” is supposed to refer to a rare event, but given the modern usage, a blue moon isn’t quite that rare or unpredictable anymore—you get two full moons in a single month, on average, every 2. 7 years. Still, it’s a nice phrase to indicate a generally rare or unexpected event of ambiguous actual scarcity, such as “When the 6-year-old unloads the dishwasher without a reminder,” or “How often the 6-year-old cleans his room thoroughly without being told.” Perhaps we’ll see a similar uptick in these kinds of events in 2018!

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Photo Credit: Graphic design by Anna Soltis. Following images courtesy of author. 

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