Sorry Ryan. I misstated what I was saying. One does not always subtract 180. In cases where the stated value is 180 or greater one would subtract 180. But for values less than 180 one adds 180. Part of my confusion comes from my aviation background. In flying 0 is always north, 90 is always east, 180 is always south and 270 is always west. Apparently in astronomy it's just the opposite with 0 is south, 90 is west, 180 is north and 270 is east. I did some poking around on the web and it appears all land, sea and air navigation have 0 as north and 180 as south. So it does seem a bit odd that astronomy would use the opposite. But with Daniel noting that surveyors also use the opposite apparently astronomy isn't the only one using it. So today I learned something new. :) patrick On 05 Sep 2014, at 17:07, Ryan Simpkins <astro@ryansimpkins.com> wrote:
I am not very smart...
Is the answer because it is easier not having to deal with negative degrees? Subtracting relative degrees from 180 will never get you in to negative territory like subtracting from 0 will. By basing all relative calculations from 180 you can't ever get in to those situations (unless you start spinning in circles I suppose). It also means you don't have to be worried about 0 being equal to 360 except in the case when it is.
How this makes trigonometry easier I have no clue. Trigonometry is already in the 'super-advanced' category in my opinion. I don't think there is a way to make it easier other than to avoid it entirely... Which I gather might be a problem if you want to launch a rocket or change orbits.
-Ryan