Full Chisel Blog

October 30, 2010

Can the Sun run any slower?

Filed under: Historical Material,Instruments,Nautical,Of Interest,Proper Tools,Uncategorized — Stephen Shepherd @ 7:35 am

I know it happens every year at this time.  You pull out your trusty sundial, set the gnomon, orient to north and you get a reading that is over 16 minutes SLOW.  It has to do with the position of the sun everyday at noon.  When plotted over a year it forms an irregular figure 8.  And this time of year it is at its slowest.  In order to get an accurate reading you need the equation of time or an analemma, like the one below.

The vertical numbers are the declination of the sun and the horizontal numbers are minutes.  On the horizontal scale to the right of 0, it is plus or fast and to the left of 0, is minus or slow.

So keep this around to correct your sundials.

And yes it will run a bit slower before it starts to speed up.

Stephen

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