Thursday, November 9, 2017

skiptember stars

[Edit, November 15: longtime BattleTech author Blaine Pardoe has posted some of the original BattleTech maps - with z-axis notations! /Edit]

Usually I spend only a few days each summer poking at BattleTech's starcharts.  Spent a little more time this autumn because someone was asking where to put Rigel.

(Here's the data I'm working from. I transcribed it from a copy of the Yale Brightstar Catalogue in spring of 2014; haven't fixed the entry for Peacock because I lost the key to the raw data.)  

BattleTech's 1980s stellar coordinates seem to have been generated systematically. Although mirrored left-to-right from how an astronomer would plot them, they do a pretty good job matching the stars' real life Right Ascension; and although the distances seem wonky, they do show a general shortening as if being projected onto a plane.

Picking out meaningful trends is extra hard because, in real life, stars aren't distributed randomly or evenly. They naturally appear in lines, curves and circles across Earth's night sky. Also, the sample is biased.

I figure I can minimize a lot of those confounding factors if I do the simplest thing possible, and the simplest thing I can think of is to look more closely at the slight differences between BattleTech's Right Ascension and real life Right Ascension.

There's a bunch of obvious sin curves there, not sure what to do with them. Why should there be an arc starting near zero degrees difference at 100 degrees RA, rising to the top right corner and then (wrapping around to the top left) falling back to zero at 280 degrees RA? Are the other curves on the bottom likewise a single curve wrapped around on itself?

Frickin' trig functions and polar math, man. Wish I were still familiar with how converting between polar systems worked.

If I don't get any bright ideas about this Right Ascension thing, my next step is probably to take stars in groups of three and calculate what angle their plane forms relative to Earth's, for as many groups of three as I can stand, and see if any patterns emerge from that.

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