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Barleywine  Barleywine is offline
Elder Jabberwock
Join Date: 10 Jun 2011
Location: Where the wild things are
Posts: 9,055

Originally Posted by Minderwiz View Post
It became clear that in order to do the calculation it's necessary to convert sidereal longitude into tropical longitude, because of the nature of the spherical geometry involved.

Now if I'd not waded into the calculation line by line, I'd not have become confused and tracked it down to Gansten's use of sidereal charts and the need to convert to tropical in order to do the maths. But as you're mathematically inclined (like me) you may well come across the same headache LOL.
The spherical geometry involved confused me to no end when I first started out. I finally had to draw my own 3D model just to figure out what was going on in three-dimensional space with all these planes and angles.

On this very (or at least related) topic, this evening I unearthed a 1976 Journal of Geocosmic Research in which Rob Hand explained why it's more accurate to use geographic/astronomical latitude in chart calculation rather than geocentric latitude. It has to do with the Earth being an oblate sphere, flattened a bit on the top and bottom. For years I always made the 11' subtraction from the atlas values to make this correction. I didn't notice the option being offered in the computer programs I use now. Wonder which one they use.
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