Saturday, March 19, 2011

A Fuller Moon (For a Limited Time Only!)

This week, an eyes-on-the-sky, neck-craned-up word.
perigee (PAIR-uh-jee) — 1. the point nearest the earth’s center in the orbit of a moon or satellite. 2. the point in any orbit nearest to the body being orbited.
Though the term would otherwise be unknown to those who don’t think much about the night sky, it’s in the news this week, for tonight our moon reaches its perigee. What’s more, it’s also a full moon, meaning that it will be particularly bright — 30 percent more so than when it reaches its apogee, or the point in its orbit farthest from Earth. (It’s odd, but I knew the word apogee, though I can’t remember ever hearing perigee until this week. Probably why I was fired from my job as a moon doctor.) This “supermoon,” according to the Washington Post, will also be the “biggest” since 1993.

a brighter moon, though you have little basis for comparison

Strictly speaking, the implications of this celestial IMAX show are limited to the tides, though I’m sure plenty of people out there would like to blame the closeness of the moon for the various calamities befalling our planet. I’ll leave that debate to religious nuts and scientists to duke out. I’m more concerned today with the language of celestial movements.

Perigee, according to the American Heritage Dictionary, comes from French, which got it from the Medieval Latin perigeum, which in turn got it from the Greek perigeion. And that word breaks down into peri- — meaning “around,” like in perimeter, or “near,” as in perinatal — and , meaning “earth,” like in geology and related to Gaia.

For those who closely study these matters (and who apparently want to confuse and exclude novices trying to listen eavesdrop on them for god-knows-why), there’s a whole cryptic vocabulary for the closest-to and farthest-from orbit points, or the apsides (singular: apsis). So, like, perigee and apogee refer to specifically to Earth, while the sun gets perihelion and aphelion (both from the Greek helios, “sun”) to describe the objects orbiting around it. And the movements of stars within a galaxy get perigalacticon (closest to the center) and apogalacticon (farthest from the center), both of which are awesome. Really. Say them outloud. Movement of bodies around stars (as opposed to our sun) get periastron and apostron. And black holes get three options: perimelasma, peribothra and perinigricon for the points unfortunate enough to be closest to this gaping nothings, and apomelasma, apobothra, and aponigricon for the presumably safer points farthest away. (Melasma, a skin condition, simply means “dark spot.” I’m not sure where bothra or nigricon come from, though I’d guess the latter has something to do with the color black.)

For the other planets and Earth’s moon, the vocabulary devolves into the kind of multisyllabic unpronounceables common only to sci-fi novels and medication brand names. Here they are, as short as I can make them:
  • Mercury gets perihermion and apohermion, after Mercury’s Greek counterpart, Hermes.
  • Venus gets three: pericytherion, pericytherean and perikrition. (The “apo” group looks just like you’d expect. In fact, I’ll just leave those out from here on, since they’re all the same roots.) The first two come from the Greek island Cythera, which sits near where Venus was supposedly born from foam in the sea. Why choose this? According to Wikipedia, because the proper adjective form of Venus, venerean, sounded too much like venereal, and a similar situation prevented them from using the goddess’s Greek name and calling all things from the planet Venus aphrodisial. Thus, cytherean got a chance at the big time, and apparently was used in science fiction writing to describe Venus-born oddities in the first half of the twentieth century. Perikrition apparently comes from Kritias, which which Wikipedia describes as “an older name for Aphrodite,” which, considering how old Aphrodite must be, sounds funny to me.
  • For our moons, it’s once again wonderfully complicated. Periselene (from the moon titaness Selene), pericynthion (from Cynthia, another name for Artemis), and perilune (from Luna, the Roman version of Selene) could be used interchangeably. And, really, who’s counting? Why don’t you just go ahead and do that? For certain astro-nigglers, however, pereiselene refers to artificial bodies, perilune to objects launched from Earth’s moon, and pericynthion for objects launched “elsewhere,” whatever that means. NASA apparently chose pericynthion to describe the Apollo project.
  • For Mars, it’s periareion and apoareion, from the Greek god Ares.
  • For Jupiter, it’s perizene and perijove, though Wikipedia perplexingly notes that the latter is “occasionally used” and the former is “never used.” I guess people just don’t like talking about Jupiter?
  • For Saturn, it’s perikrone and perisaturnium, though the former (from the titan Kronos, the king of time) is preferred.
  • For Uranus, it’s periuranion, because this planet was actually given the name of the Greek version of the god and not that of Caelus, his Roman equivalent.
  • For Neptune, it’s periposeidion, after Poseidon.
  • And for that poor nothing Pluto, it’s perihadion, after Hades.
I can’t explain exactly why I find this all so fascinating, but I suppose it’s probably combination of me being a mythology nerd and me being impressed that planetary scientists actually thought this naming system through, deciding that since the peri- and apo- prefixes were Greek, they would combine more smoothly with Greek gods’ names instead of the Roman ones. Or perhaps these guys, being scientists, decided to keep the formulas pure, as they would in any other setting. In any case, the resulting words, clumsily Greek though they may sound and look, create this beautiful bond between old world religion and the most fascinating studies about our giant galaxy that I find rather touching.

And, just so I conclude on a note that doesn’t sound so schmaltzy, I’ll point out that Autocorrect, you naughty rascal you, kept repeatedly trying to turn perigeum into perineum.

Planets and such, previously:
Previous strange and wonderful words:
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  1. You mentioned the term "apsides", which comes into play if you *don't* want to worry about all of those terms for specific bodies: the generic term for when a satellite comes nearest to its primary is "periapsis", and when it's furthest away "apoapsis".

  2. True, true. But I'm never one to ignore weird words when simpler ones could be used.