Supermoon: 19 March 2011

Supermoon with Double Halo over Salmon Harbor in Winchester Bay, OR

I can’t believe I didn’t even note the amazing full moon we experienced on March 19th!  In my defense, that was the day after Finals Week ended, and I was pretty much good for nothing.  In fact, all my mental state could handle was “ooh!  Sheep!” as I drove up to Portland that day.  Noting the occurrence of a moon perigee and trying to determine how its energy was influencing me was a bit beyond my ken.

Still, we did experience a moon perigee that fell in conjunction with a full moon, which the media of course termed “Supermoon” or a “Super Perigee” and caused a lot of confusion for a very simple concept.  Basically, a moon perigee occurs when the moon is at its nearest point to earth in its elliptical orbit, roughly 356,600 kilometers.  Conversely, and apogee moon is when it is at its farthest point from earth, or about 406,400 kilometers.  Since the moon completes a full orbit about the earth once every 27.3 days, it is at both perigee and apogee points at least once a month.  No big deal.  In fact, we usually hardly notice it thanks to the fact that our eyes and brains can’t readily compare the size and brightness of objects observed on separate occasions.  When the perigee or apogee falls at about the same time as a full moon, though, the difference becomes visibly noticeable to many people, and with good reason:  a perigee full moon is about 14% bigger and 30% brighter than an apogee full moon.

This past Saturday’s full moon occurred 1 hour before the moon hit perigee, which made for a really big and bright full moon.  It’s also pretty rare that fullness and perigee get that close:  the last closest full moon perigee was in March of 1993, and fullness occurred 3 hours before perigee then.  There were some physical effects of the conjunction:  tides were more exaggerated than they typically are, and some astrologers say that some of the recent natural disasters like the March 11th earthquake and tsunami that rocked Japan are attributable to this lunar event.  However, the key word in that latter speculation was “astrologers”, which–of course–are not scientists.  Past full moon perigees have often passed without event, and unless the event happened at the same time as the full perigee, there wouldn’t be much evidence of a correlation anyway.  Over a full week of time elapse–essentially a quarter of the moon’s orbit–sort of kills the correlation altogether.


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