[time-nuts] Local Solar Time Clock

Brian Lloyd brian at lloyd.com
Sun Jan 19 08:35:56 EST 2014


On Sat, Jan 18, 2014 at 10:09 PM, David J Taylor <
david-taylor at blueyonder.co.uk> wrote:

> I am looking for a physical clock (not software) that will indicate local
> solar time. IOW when the sun is at its highest point, the clock would
> reliably read 12:00 throughout the year.
>
> Is there a commercial product or kit available for this?
>

For a mechanical clock, probably not. The problem is demonstrated by what I
suggested that you do with a stick and pebbles. By marking the position of
the sun to locate the point where the sun is highest in the sky you
identify local solar noon. By marking the position of the sundial's shadow
at a fixed time every day relative to GMT you will find that, over the
course of a year, your shadow will inscribe an analemma, whose lateral
displacement represents the correction factor between sidereal (GMT) noon
and local solar noon. This is all caused by the tilt of the rotational axis
of the earth which causes the poles to be displaced either advanced or
retarded relative to the centroid at the equinoxes. (Equinoxae?) So your
mechanical clock would need to speed up and slow down in a smooth fashion
twice over the course of a year. Pretty hard to do with a mechanical clock.
Definitely a job for a uP.

BUT a really cool thing would be to interface a camera to find the point in
time where YOUR local noon actually occurs and corrects the clock.
Automatic meridian circle anyone?

-- 
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067


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