I published this last year in another space, but a full moon discussion over dinner at the home of some friends reminded me of this piece, so I will serve it up here.
Many of my subscribers have written recently to suggest that I should not write, in this aMusements column, about drinking beer; so, in the following article, in deference to their sensitivities, I avoid the mention of beer all together.
There was a full moon two days back on November 26th. I checked the calendar. There will be another on December 26th. That is 30 days apart. ” What the hell happened to the 28 day lunar cycle??” I thought as I sipped my rum and looked at the moon with my binoculars a couple of nights back. So, of course, I Googled a bit to see if there was an explanation. I found this one…
The orbital period of the moon from perigee to apogee and back to perigee is called the anomalistic month. The period of the moon’s phases, that is the motion of the moon with respect to the sun, is called the synodic month. The ellipticity of the moon’s orbit also causes the duration of a half-lunation to depend on where in the elliptical orbit it begins and so, effects the age of the full moon.
The average duration of the anomalistic month is approximately 27.554549 days; while the average duration of the synodic month is approximately 29.530588 days.
The fumocy is slightly more than 14 synodic months and slightly less than 15 anomalistic months. Its significance is that when you start with a large full moon at the perigee, then subsequent full moons will appear ever later after the passage of the perigee. After 1 fumocy, the accumulated difference between the number of completed anomalistic months and the number of completed synodic months is exactly one.
” Hmm,” I thought. ” I’d better have another rum.” So, I did; and, as I stared in marvel at that floating orb, so beautifully reflecting the light of the sun, I reflected some more on what I had read. I saw some sense to it. Where in the ellipse the moon was when it was full one night might determine the time span to the next full moon. Maybe. There had to be more to it. I sipped my rum and I pondered the mystery. An hour later, I was no more enlightened. I was, however, a little bit buzzed; and it was this dual intoxication of moonlight and moonshine that lead me to the conclusion that, despite any pretense to the contrary, I don’t know shinola from synodic.
I have learned that the anomalistic moon cycle is close to 28 days, but that the synodic, or full moon, cycle is about 29.5 days. Now I am left to wonder if anomalistic is synchronistic or synonym-istic with animalistic and that, perhaps that might explain werewolves, menstrual cycles and the periodic madness of imbibing the demon rum.
The degree of my ignorance is staggering I realized as I made my way to bed. It is lunacy to pretend otherwise; but how else can I make it through the days of my life, except that I imagine I know a thing or two about the moon and why it does what it does every 28 or 29.5 nights or so.
By the way, sugar cane is traditionally cut on full moon days to maximize the yield of juice. Cut the cane on a full moon day and reap more juice to make more rum. That’s a good thing since people seem to drink more rum on full moon nights. I, of course, will never touch the stuff again, full moon or not. Well, perhaps on a blue moon, which happens, on average, every 19 months; although I am not exactly sure whether that is anomalistic or synodic months.