# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Latitude from two altitudes
Date: 2017 May 18, 18:57 -0400
Hello Bill Anders

Frank asked us to help him out.

Copies of Bowditch, from the 1800's, contain an entire chapter on Latitude by Double Altitudes.  From Bowditch, 1849, Latitude by:
1) double altitudes of the sun
2) double altitudes of a star
3) double altitudes of a planet
4) double altitudes of the moon
5) altitudes of two different objects, taken at the same time
6) altitudes of two different objects, taken within a few minutes of each other, by one observer
7) altitudes of two different objects, taken at different times.

Don't have an ancient copy of Bowditch?  Never fear, we have them here in the library!

On May 18, 2017 2:55 PM, "Frank Reed" <NoReply_FrankReed@fer3.com> wrote:

In the lat/lon from a photo thread, Bill Anders wrote:
"Moving on.... Is there a general mathematical solution to this problem? The class I'm working with is relatively advanced (some trig, some calculus), so math difficulty is really no issue. Ignoring longitude, if I measure the altitudes of two known stars with some exactness, is there a formula that will tell me my latitude? Frank, I read your messages about the Orion North Arrow in your NavList library here: http://fer3.com/arc/m2.aspx/Orion-North-Arrow-FrankReed-feb-2017-g38274. I understand that the arrow is intended for a rough measure of north direction and latitude, too, but for a related example: if I measure, very accurately, the altitudes of Betelgeuse and Rigel as Orion is rising, could I get my latitude directly???"

I am really busy right now, so I am hoping some of the rest of you out there can address this. Obviously this can be done by standard plotting of two lines of position with an arbitrary longitude, but I assume Bill is looking for something more direct. Any ideas?

Frank Reed

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