Polaris and the variation revelation

After 8 days of frantically scribbling numbers into my notebook varying amounts of light I now had a lot to catch up.  Having finally understood sun sight reduction it was time to get to grips with the Moon, planets and the stars.  My quest now, whilst maintaining my sun-run-sun routine, is to work through all the sights taken so far and get them plotted on the chart.  We are at least solar navigating now.   I will have nailed this by the end of the trip.  1730 and that is enough of the books, this would be my routine for a while.

  It transpires that on our first night at sea I had taken what would prove to be a lovely fix using the Moon and Polaris (North Star).  The calculations for the Moon are only moderately more complex that those for sun sight reduction, thus equipped with Favourite Books 1 and 2 and following Mr Cunliffe’s step by step instructions we soon have a position line from the Moon.

  Polaris hangs in the low northern sky and is the central point above which the heavens rotate above our heads.  This wonderful lady is the tail of Ursa Minor, or the Little Dipper and easily identified when Ursa Major (The Plough or the Big Dipper) rises, the bright stars in the “handle” of the plough point unmistakably at Polaris and continue to point at her all through the night, the centuries, the eons.

  While the Sun only lunches once per day at noon, Polaris is at lunch all night, so we can ascertain our latitude from her at any time our horizon is visible, which with a bright full Moon could be all night.  The calculation for accurate latitude from Polaris turns out to be an incredibly simple.  We go through the routine outlined in the book, apply the numbers correctly and bingo we have our latitude.  The calculation itself is basically add a degree and a bit, add a bit, add a bit more and then subtract one degree, which effectively means that even without applying any corrections to the sextant sight Polaris should give your latitude to within half a degree (or 30 miles).  And with that I have two lines on a plotting sheet which cross at our position – YES!!  Lovely.

  And now I see how Columbus discovered compass variation as he crossed the Atlantic.   It has baffled me for years how sailors could have known about magnetic variation, whose rate of change would be tiny on a daily basis on board a ship.  But of course, with Polaris hanging in the sky like the true North Pole’s lighthouse beaming out a light saying “north is here” sailors would quickly notice that their compasses didn’t point north.  

  When “crossing the pond” changes in variation become more apparent.  On the eastern side our variation was around 8 degrees west, now more than half way across our variation is up to 13 degrees west and will keep rising as we travel toward the Caribbean.  There must have been some clever minds back then to notice this phenomenon, to work out what it is and to calculate it.  Once again my brain explodes at it all.  

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