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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant arc length
From: Stan K
Date: 2015 Sep 16, 21:40 -0400
From: Stan K
Date: 2015 Sep 16, 21:40 -0400
Brad,
Nope, never saw it coming. I would hardly call a circle of reflection a "standard marine sextant". Nevertheless, I did enjoy your talk at the 2010 Nav Weekend at Mystic Seaport.
Stan
-----Original Message-----
From: Brad Morris <NoReply_Morris@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Wed, Sep 16, 2015 9:27 pm
Subject: [NavList] Re: Sextant arc length
From: Brad Morris <NoReply_Morris@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Wed, Sep 16, 2015 9:27 pm
Subject: [NavList] Re: Sextant arc length
Stan
You had to know this one was coming.
Unusual, but still obtained on the open market, for a mere arm and a leg, a circle of reflection. Largest marking on the arc is 310°, however, the greatest measurable angle is 282°. Being a circle, there are actually two arcs, of identical disposition.
And no, I have yet to measure any angle that large!
Brad
On Sep 16, 2015 3:31 PM, "Stan K" <
NoReply_StanK@fer3.com> wrote:
What is the largest usable angle that any standard marine sextant you know of can measure? I have one where the arc is marked to 150º, but the index arm hits the horizon shade bracket just shy of 130º.
I put limits on just about everything in my Celestial Tools program, so ridiculous entries are automatically flagged, e.g. limiting longitude to 180º. In the earlier versions of Celestial Tools I limited the degrees of sextant altitude to 140. In V4.2.0 I changed it to 150, then back to 140 in V4.4.0. This morning I was looking at a 1977 Bowditch and found a back sight problem where the sextant altitude was 141º04.9'.
It is easy enough to change Celestial Tools, but now I am curious to know what is actually out there. Looking at a bunch of old Celestaire catalogs, the largest arc I can find is only 135º, which I have to believe is a usable angle. What do your sextants have?
Stan
