For those unfamiliar with horology, look at the Wikipedia under
"equation of time"
This is the relationship between solar time and the average or "mean
time".
It is mainly the sum of two sine functions, one of 6 months frequency
the other
one year. Amplitude 16 - 17 minutes.
This function allows a mean time clock to show the time of noon each
day (passage of the Sun
through the meridian)
cheers,
Neville Michie
On 24/01/2012, at 3:59 PM, J. Forster wrote:
At the solstices, the derivative of the declination goes through just
about to zero, just like a sine wave.
-John
==============
It might be useful to determine the rate of the sun's movement at
the ends of the analemma.
There is a passage grave north of Dublin, Ireland, that has a long
passage from a shadow box above the entrance to a spiral carving on
the rear wall. Light shines on the carving at the winter solstice.
The waiting list to see this event fills up with New Agers about a
year before the event. I asked our guide if that wasn't very hard
on people who could only see the event on one day if that day was
cloudy. "Oh, no," she said. "The event happens for 3-4 days on
either side of the solstice."
Of course, a passage grave is not the same as a shadow cast by a
fine wire on a microscope. It might take a few years to locate it
properly.
Are there any timenuts that want to be buried in a passage grave?
Bill Hawkins
-----Original Message-----
From: Chris Albertson
Sent: Monday, January 23, 2012 8:40 PM
On Mon, Jan 23, 2012 at 6:07 PM, J. Forster <j...@quikus.com> wrote:
I think you'd want a slit, not a pin hole. The pin hole would be
better but it would only work one day a year.
Actually two days per year, unless it was adjusted for the summer or
winter solstice, then it'd be one.
I still think it is "one". because there are not an integer
number of
days per year so you don't get and exact repeat in 6 months.
Maybe a
pin hole would only work once ever? I don't know. To "work" the
pinhole has to exactly line up with the detector at the exact same
time of day.
But I'm not liking slits either because I can't see how to adjust
them
to exact vertical.
I'm back to the first thing I thought of, a wire with a large
weight.
Then you measure the light curve as shadow of the wire sweeps over
the detector.
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