A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Dec 20, 13:03 -0800
I hope to get to a longer, more general reply on this topic later today, but for now I have to comment on this one. Gary LaPook wrote:
"although mine does more, it calculates the time of twilight and is automatically set for that time"
This is a great function, which, I should say, a number of folks have independently invented, and it's something that a navigator's star finder should have had right from the beginning. The single most reasonable use for a star finder is setting up for evening twilight. And this can be done entirely by a turn of the wheel if the base plate includes a labeled ecliptic and if the altitude-azimuth overlays include arcs for an altitude of -12° (or some reasonable point for nautical twilight). All the navigator should have to do is rotate the overlay (for the nearest latitude, of course) until the twilight altitude arc crosses the correct date on the ecliptic. And that's it! Immediately read off the altitudes and azimuths of the stars. No calculation and no almanac required.
The big issue with the standard Rude/H.O. 2102 star finder design is, quite simply, that it is a bad design. It's poorly done, and it's rather intricate to use. The design takes everything from a common planisphere ...and screws it all up.