How to measure a Sky Dome.

From: Alex Ferguson <abf_at_interzone.ucc.ie>
Date: Wed, 25 Mar 1998 15:40:39 GMT


There seems to be some confusion of whether/how one can determine the size of the Sky Dome in Glorantha, or at least some vagueness. Apologies for belabouring what will be obvious to some (and painfully like high school trig for others), but I feel moved to demonstrate that one can, given reasonably accurate surface distance measurements, and instruments such as a sextant.

Stand at any given point on the surface world, and measure the angle above the horizon of some celestial object. Pole Star is convenient, for a number of reasons. Call this angle 'A'. Now take the same measurement 'd' Key Miles directly towards that object, and call this angle 'B'.

Then the Pole Star is at height: d (sin A) (sin B) / sin (B - A) km.

If one has access to a baseline of, say, 1000km, then you can detect parallax of objects up to maybe 100,000km away (with rapidly decreasing accuracy).

Yes, this is point-headed, and non-hipster-cool (thank ghod). Let's not forget that Glorantha has its pointy-heads too, though.

Slainte,
Alex.


Powered by hypermail