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    Re: Noon Longitude by Equal Altitudes
    From: David Pike
    Date: 2021 Nov 23, 13:00 -0800

    Well, wonders never cease.  Today we had a second day with an hour of sunshine either side of noon, and I was ready to take observations.   This time my result was 1.4nm north and 1.6nm east of my known position.  I had decided to carefully sit the Sun on the horizon graticule and add 16.2’ to my Hs.  I rather like this method on the ground, but I don’t think it would work well in the air on a bumpy day.  Your aim needs to be a bit more basic than that for a one-minute observation chasing the graticule.

    Today’s result was close enough for me to start worrying about a refined refraction correction.  I found temperature and sea level pressure from RAF Waddington at 12.00 online and delved into Nories.  Unfortunately, the refined refraction put me 0.5nm further away, so I quickly rubbed out my working and decided to stick with the AP3270 refraction value.  I really need to take more care over calculating a set of refined instrument error corrections, but with a separate correction required for each 10 degrees stop on an RAF Mk2, and three such sextants to play with, let alone my MkIXs, that could take a while.   

    Continuing into ‘Little Ships – Astro Navigation' tempted me to try something else I’ve not done before, an ex-meridian latitude.  I decided to assume the sky had clouded over after my first observation this morning and delved into pages of Nories I’d never visited before only to find that my efficiency in observing in good time put me outside the ex-meridian LHA limits.   Therefore, I decided to cash in on my inefficiency of last night and assume the same had happened for my Jupiter observations.  After much head scratching and rubbing out, I came up with a latitude of 53.08.3, 1.5nm below my known position.  Using Nories refined refraction tables would have put me 0.5nm closer this time.  My homework is attached for marking.  DaveP


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