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    Emergency Declination Calculation
    From: David Pike
    Date: 2022 Jun 30, 06:47 -0700

    We have seen how useful knowledge of the Sun’s declination can be if you are suddenly cast adrift in an open boat in the middle of the night.  But what if you have nothing with you but drawing instruments and the Gunner’s back to draw on, and that knock on the head you got has made you forget yesterday’s value of declination.  Could you still work out a reasonable declination value?

    I found an approximate formula for declination based upon a perfectly circular, 365 day Earth orbit of Dec Sun = -23.5cos(360(d+10)/365) where d is the number of days from 1st Jan, but I still needed cosine values.  I put Navigator, Tech Drawing Master, and Lower Set Maths Master experience together to come up with the attached.  For 28th April 2022, not 1789, I managed to find a declination value within ½ degree of the true value.  I expect someone will know an easier method based upon nothing more than the slope of the Moon’s horns, the colour of the sea, or the sight of land birds, but comments please anyway.  DaveP


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