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.
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 gē, meaning “earth,” like in geology and related to Gaia.
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.
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".
True, true. But I'm never one to ignore weird words when simpler ones could be used.