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Re: Winter Sextant Sight Accuracy?
From: Jared Sherman
Date: 2002 Jan 10, 6:35 PM
From: Jared Sherman
Date: 2002 Jan 10, 6:35 PM
George- Latitude about 43N and tht puts a late afternoon sun around 11-12d above the horizon. I am aware of the possible errors, causes, and effects and did in fact run them all through a calculator to see just how far a change of 5F or 50mb or eye height would affect things, I have notes on exactly how far each can affect the readings. And I am aware of sextant index error which I think was the root problem--the index zero wheel may have loosened under my gloved hand, I will be checking this again and have since re-zero'd on a star which gives me a far tighter zero. The effect of taking a warm sextant out of the car does not exist, after an hour in my trunk near 35F the sextant is nicely prechilled thank you.The question remains: Has anyone found that it is harder to get absolute accuracy when shooting an afternoon sun from a lattitude 43N during the winter, when refraction causes the three factors of eye height, air temperature, and air pressue to be far greater in effect than they are for a typical summer sight from these same lattitudes? I also suspect that some mirage (from the ocean/air temperature difference) and a rough horizon (either thermal mirage or waves at sea) were involved. I wasn't getting a real crisp sight and I've gotten crisper before, I'm wondering if that air/water temp difference causes enough distrotion in the winter to make it something to routinely be mindful of.