DECLINATION LINES
June 13, 2010
The free booklet Declining Shadows (and its
DeltaCAD macro (calendarDeclination.bas) here,
and you can set the declinatio values) are very
well worth downloading. This is only an extract
from the section in Illustrating More Shadows
which deals with calendar curves in depth, and
discusses several trigonometric approaches, and
provides complete tables for a wide range of
style heights (latitudes). Also
see here.

The DeltaCAD
programs display calendar curves,
as does one of the JustBASIC
programs, and of
course the main spreadsheet  
reference-spreadsheets.xls which has many ways
of calculating declination line data.

The DeltaCAD macros provide for animation
showing how declination curves vary. They also
show how they vary by nodus to dial plate height,
or, by style length. The results appear
inconsistent, but they are not, and as with all the
DeltaCAD animations, they are highly instructive.
For other dial furniture, look at the Italian line page page
For other dial furniture, look at the analemma page
The analemma page has excellent DeltaCAD macros discussing not just the analemma, but also the
calendar curves.

However, this
calendarDeclination.bas macro allows you to specify the declination values to use for all
the dials, whereas the
analemma.bas macro has fixed values except for a few cases.  

The analemma uses the EOT (equation of time) together with the sun's declination to derive the
analemma, and that same declination is the basis for calendar curves. Actually, that is true for armillary,
equatorial, polar and meridian dials. For horizontal, vertical, and vertical decliners, the sun's azimuth
and altitude are used as well. And those
analemma notes are helpful in understanding what is going
on. Chapter 24 of Illustrating Time's Shadow is by far the best description available. I think.
For calendar curves on any hour
angle dial with
analemmas,
check this page here. However,
this
calendar macro allows more
flexibility on specifying declination
values.
DeltaCAD V7 changed how "dcMirror" worked, I have
a workaround that works for most, but not all, of the
text that the V7 function altered.
 April 24, 2010Also,
DeltaCAD v6 and v7 differed on handling a -ve single
as a paremater, fixed.  
 June 13, 2010