NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ian Gifford
Date: 2026 Mar 22, 15:30 -0700
Hi David C.,
>I will get back to you tomorrow with some further details.
I am sure Frank will provide the details you are looking for; meanwhile, the following was posted by Frank back on 1Apr23; last paragraph:
<snip>
* The ABC method is what I teach in my modern celestial workshops. You calculate the HA of the Sun from the standard spherical triangle:
cos HA = (sin alt - sin Lat sin Dec)/(cos Lat · cos Dec) or equivalently,
HA = acos(cos ZD / cos Lat / cos Dec - tan Lat · tan Dec), or (as above):
HA = acos(A - B) where A and B should be obvious. And then
Lon = GHA +/- HA. You add HA when the body is rising (in the east) or subtract when it's falling (in the west).
</snip>
Source:
https://navlist.net/Venus-ONE-fast-fix-daylight-FrankReed-apr-2023-g54071
With best wishes.
Yours sincerely,
--
Ian Gifford 42° 38' N, 71° 24' W
