A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 Oct 14, 08:53 -0700
Bob GW you wrote:
I'm a self taught celestial navigator so my education may have holes, but when I look through my sextant I can see both the image and reflection of the celestial object easily through the clear glass half of the horizon mirror. The clear glass has reflecting properties. It's easier to see the horizon and the celestial object simultaneously than to have the celestial object on the mirror side and the horizon on the clear side. Also at the line where the mirror meets the clear glass on my Astra IIIb knock off (GLH130-40), the interface is partially silvered acting as a half mirror. This truly allows both reflection and transmitance at the same mirror location. In the various references I've read, I haven't seen any mention of this. Is this common knowledge, but no one seems to mention?
Thank goodness for that. I thought it was just my eyes, or the age of my sextant. True the books don’t mention it, but they happily tell you to swing the sextant like a real sailor man to find the vertical, and there wouldn’t be much point in doing that you weren’t getting a reflection of the body from the clear horizon glass for at least some of the swing.
It’s more of a problem using an artificial horizon, especially if you’re an edge to edge enthusiast. It’s sometimes a job working out which image is which. Occasionally 32 or 64nm errors start appearing. You might need to tinker around with different shades. If you’re a body over body, just for fun, philistine like me, it doesn’t really matter which image is which. DaveP