Monday, June 24, 2013

Supermoon

Last night was a supermoon, thus the coincidence of a full moon taking place very close to the time when the moon is closest to the earth. In matters of astronomy, someone like me, who tends to be geometrically challenged, can never remember exactly what this sort of things means. Hence I don’t apologize in repeatedly revisiting such subjects: at least for a week or two I can remember the relationships of these mysterious bodies hanging in the sky.

The moon’s orbit around the earth is ever so slightly elliptical. Hence at one point in its travels it is closest to the earth (perigee), at the other farthest (apogee). The image I show comes courtesy of the Physics Department of Utah State University (link). The words are from Greek, peri meaning near, apo meaning away, and the ge is derived from the Greek for earth; we get Gaia from that. The official name for this point in the lunar cycle is called Perigee Moon. “Supermoon” was a very recent coinage by the astrologer Richard Nolle in 1979 (per Wikipedia).


The graphic, as noted, exaggerates the ellipse. The inset, also from Wikipedia, shows the difference in perceived size of the moon at its last perigee before yesterday (on March 19, 2011) and its more or less average size (on December 20, 2010). The difference between perigee and apogee according to NASA is 14 percent, but The Huffington Post shows 13 percent, which pleases this tiny subset of humanity here. Supermoons occur once every 14 full moon cycles, thus  roughly every 378 days—just long enough to be news every time, weather permitting, of course, while the memory of why the moon should now seem so much brighter and larger will, each time, have been once more forgotten. That’s when blogs come in handy to have a private reference… How can those monstrously big jets stay in the air? (one of Brigitte’s favorite questions). How can that moon stay up there rather than falling down into the pit of eternity?
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See the correction a year later here.

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