You may be interested in the attached chart of the Equation of
Time for 2011. It is of interest for a number of reasons...
-
it
is an 'intrinsic' plot - not the familiar cartesian, polar or
analemmatic form.
An
intrinsic plot has equal increments of the
independent variable along the curve of the plot rather than
along the x-axis.
This
allows the curve to be folded - making a very compact form.
- it
is much easier to read than a normal plot, because the day
points are all equally spaced along the curve.
- it
looks good !
The use of an intrinsic plot for the equation of time was
first used in the Bury St Edmunds dial in the 1860s. See F.
Sawyer: ‘The Bury St Edmunds
Curve’, NASS Compendium 12(3), p.29 (Sept 2005) or John
Davies: 'More on the Equation of Time on Sundials', BSS Bull
17(ii), p.75 (June 2005).
This particular 'Flame' form is one of many possible
compact folded forms that can easily be generated with a
spreadsheet.
For the number-obsessed, the chart is very precise. Though you
cannot of course read it on the chart, the values of EoT are
exact to within a fraction of a second, since I have used the
2011 polynomial algorithms issued to surveyors and
navigators by HM Nautical Almanac Office. The chart is for
noon UT. If anyone would like a copy - correct for their own
time zone and longitude - please let me know. Or if you are
familiar with Excel, you can download the spreadsheet used to
draw the curve from
http://www.precisedirections.co.uk/Sundials/Index.html.
The file is called "Almanac 2010_2011.xls". This has all the
polynomial coefficients for the Sun and navigational stars for
both 2010 and 2011. You can see a number of other intrinsic
plots of the EoT at the above website. Click on the
'Grange-over-Sands Conference' link.
For the really observant, you will notice a tiny additional
gap between 31 Dec and 1st Jan: that is there because there
are 365 1/4 days in a year not 365...
The zodiac signs on the chart mark the day starting the
astronomical constellations when the Sun's longitude are
passes 30, 60, 90 degrees etc. This may not conform with the
astrological dates.
Best regards
Kevin
