True Places Never Are

Queequeg was a native of Rokovoko, an island far away to the West and South. It is not down in any map; true places never are.
—Herman Melville, Moby Dick, Chapter 12: "Biographical"
Damn but space coordinates are confusing. I was trying to figure out how zledo work the galactic coordinate system; I wanted to rename their stars so they're their actual coordinate (i.e. something like the Bonner Durchmusterung—"Bonn Observatory Perusal," roughly—star catalog, which lists each star as "BD" followed by its declination). The center of the galaxy, Sagittarius A* ("Sagittarius A-Star"), is 26,673 light years from Earth, give or take 42; our "galactic" coordinate system puts the sun at the center and runs one of the planes not through the actual equatorial plane of the galaxy, but through the sun, which is about 56.75 (give or take 6.2) light years above the equatorial plane.

That was only one headache; I also think that coordinates for anything round (like a galaxy) should be polar—especially for the zledo, who conceptualize orbits as movement in the sky of the center object (in this case, Sagittarius A*), and refer to distance from the center as "altitude", just as one might exactly describe an object's location on Earth in terms of its longitude, latitude, and elevation. So, what this means is that first I have to convert all the galactic coordinates of each star from the Sol-centered one to one centered on Sagittarius A*, and then convert those units to polar ones. (You remember that, from trig, right?) One piece of good news, I was worried that the galactic-coordinates' equatorial plane was tilted to go through Sol, but, mercifully, it's only shifted upward by 56.75 light-years. There's also the question of where to stick the prime meridian; that, zledo will stick on a line through mÕskoi (as we stuck Earth's through the Royal Obervatory in Greenwich).

Further credit given where due to our galactic-coordinate system, it appears to define north correctly, as being on your left if you face spinward (east) with your feet pointed at the center (nadir).

I worried about what units to express the distances in (spherical coordinates have polar angle and azimuthal angle, and then a distance, as two-dimensional polar coordinates have the angle and then the distance), but I actually don't have to. I can just treat, say, the virial radius of the Milky Way, which seems to be about 258,000 parsecs, as a unit circle, and then express distances as a fraction of that. Or, since the actual important part of the galaxy is more like half that many light-years—and whatever idiot called them "kilolight-years" instead of "light-millennia" should be pistol-whipped—I might use that definition of the galactic radius as my unit-circle, and express "altitudes" as a fraction of that.

But then it occurred to me, most of the West's more recognizable, systematic star names come from 1603 (Bayer designations), 1725 (Flamsteed designations), or 1879 (Gould designations); Chinese ones date to the Han (206 BC-220 AD) and Jin (266-420 AD) Dynasties, but were truly put on a systematic footing by the Jesuit missionary Ignaz Kögler, who compiled the Yíxiàng Kǎochéng between 1736 and 1744, with a revision, the Yíxiàng Kǎochéng Xùbiān, a century later, in 1844. Meanwhile we only even had our Sol-centered "galactic" coordinates starting in 1932, with a major correction in 1958.

So zledo could use an older, more Lhãsai-centered coordinate system, analogous to our right-ascension and declination one (but radians—they didn't always use radians, of course, but rather fractions of a circle, but radians' advantages eventually became clear), for naming stars. That's…not much easier, though, if any, because now, I have to define a celestial coordinate system relative to a planet whose ecliptic lines up roughly with Orion. (I checked, in Celestia: λ Serpentis does indeed have a recognizable Orion in its sky. There's probably someone who can actually tell me how the ecliptic plane of λ Serpentis is oriented, but since I can't find any such thing on the interwebs, neither can my readers—yet, probably, damn the inexorable march of science.)

Oh well. This kind of research is a necessary part of my creative process. I'll eventually hash it all out.

1 comment:

Sophia's Favorite said...

So, I tried it. Turns out the numbers you get are huge and unwieldy. I'll just stick with my current system.