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    Re: Loss of accuracy using Sun over Sun with a mercury artificial horizon?
    From: David C
    Date: 2016 Jul 18, 20:26 -0700

    The good thing about the inclement weather is that it is forcing me to think about what I am doing rather than rushing outside and taking yet more sights.

    I considered that there might be an error in recording time but I have decided that that is unlikely. Typically there is a count of 6 from taking the sight and reading the time. My count might be out by 1 sec and  the clock may be about to tick over when I read it. That gives an error of +-2 sec. The maximum azimuth of my sights was about 30°. From Norie that  gives a change in altitude of about 5.6'/min. For an error of 0.5' the time would need to be in error by approximately 5 sec (if my arithmetic is correct). For most of the sights the required time error would be greater than that.

    Secondly I selected two pairs of sights and determined longitude by equal altitudes. One sight  gave a long 1' in error, the other 0' in error. I accept that the latter was probably luck (-;   A 4 sec error gives an error in long of 1' (again if my arithmetic is correct) so time error is < 4 sec.

    Finally a noon sight, which I would expect to be the most accurate, gave a lat 0.8' high, which means i was measuring 0.8' low, consistant with the other results. There could be other isses with the noon sight. The sextant was heavy and I found it tedious waiting for max alt, even though I had pre-computed the time of LAN. I had read that the sun moves very slowly at noon but not until I tried a noon sight did I realise just how slowly!

    The above may or may not be relevant but typing it out is helping me to get a clearer picture of the factors involved in taking sun sights.

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