Hi Kevin (et al),
Great stuff! I particularly like your item 4, the dates when the EoT has values
of whole minutes. This is a useful feature for reproducing the scales on old
dials. I have possible extension to this you might like to add: many of the
larger and better-quality 'London' horizontals of the 18th century actually go
down to half-minute intervals. In addition, they give the values of the
maxima/minima as well.
Regards,
John D
-----------------------
Dr J Davis
Flowton Dials http://www.flowton-dials.co.uk/
BSS Editor http://www.sundialsoc.org.uk/bulletin.php
________________________________
From: Kevin Karney <kar...@me.com>
To: Sundial <sundial@uni-koeln.de>
Sent: Wednesday, 11 June 2014, 17:05
Subject: A few new Tables for the Gnomonist...
Dear Friends
I have been amusing myself with the astronomy of the Sun and have done a very
complete coding of Meeus' routines for finding EoT, altitudes, azimuths, etc,
etc. These deal with precession, nutation, aberration, parallax and the
differences between TT, UT1 and UTC time. This has yielded routines of much
greater precision than are generally required by the gnomonist. However the
speed of computers is such that lengthly routines are hardly noticed. So I have
produced a javascipt routine and used it to prepare 4 tables for my website.
They may be of interest to the dialist.
1) For a given civil time and location - all the usual solar parameters are
calculated (nothing much new here - other than the precision)
2) A table giving the noon Equation of Time and Longitude Correction over any
given year and location.
3) A list table of civil - v - solar time, altitude, azimuth, declination and
local hour angle - for any starting date and time, covering any increment of
seconds. (Useful if you are trying to set a dial and waiting for the Sun to
shine)
4) An EoT table of the kind used on many old sundials, where the date is given
every time the EoT changes by 1 minute. (Try changing the year from one to the
next and see the change due to the leap aye cycle)
You can find these at
http://www.precisedirections.co.uk/Sundials/
Any comments, corrections, suggestions for additional tables or facilities
would be welcome.
The input of latitude, longitude is a bit basic, but it is hoped to improve on
this. Also, I plan to produce sunrise/solar noon/sunset tables.
If you use a browser that allows you to view a web-page's source (such as
Chrome or Firefox), you can see the astronomical routine that is used.
Enjoy!
Best wishes
Kevin
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