A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2021 Sep 27, 08:33 -0700
Dear Herman, thanks for the article.
Now it is all clear. Mr Burch says:
All sextants have two sets of shades, the main ones used for all sun sights called the index shades, that cover the index mirror, and another set of usually much thinner shades called the horizon shades that cover the horizon glass, in direct line with the telescope. These are intended for removing glare on the water, which is often an issue to deal with. These horizon shades, however, are usually never thick enough to protect against a direct view of the sun as required in this measurement. I have seen sextants with a thick horizon shade likely intended for this purpose, but this is rare.
By my (very little, almost non-existent) experience with sextants - the only type that lacks dark shades for the horizon is the sounding sextant. It is only to take angles between the landmarks - NOT for CN observations.
I'm sure - the Freiberger Yacht Sextant is equipped with all the shades you may ever need for CN.
By the way, when you do the IE check by the Sun - you may also get the current value of Sun's SD - and check it against the value given in the NA. Thus, if your measured SD matches the one in the NA, you get the confidence in your measurement of the IE.
So, for now, fine-tune your sextant by Jupiter, later on - do not be afraid to use shades when sighting the Sun.