Dear Michael,
I agree with much of what you say about the
French Republican Calendar but, importantly,
you say nothing about how this calendar
relates to sundials. Let me explain in
simple steps:
1. Sketch an outline vertical sundial with
seven declination curves and a single
hour line, at 12 noon.
2. The seven curves mark the boundaries of
six regions. Note each region is divided
into two parts by the 12 noon hour line.
3. We have 12 spaces. Now write the label
CAPRICORN in the top left space. This
is the first astronomical month after
the winter solstice.
4. In the five spaces underneath, you write
the names AQUARIUS to GEMINI.
5. On the right hand side you start at the
bottom and work up with the names CANCER
to SAGITTARIUS at the top.
6. This sundial will now tell you which
astronomical month you are in. Of
course you need to know whether the
solar declination is increasing or
decreasing but everyone who reads
this mailing list will know that :-)
7. Now, just for a moment, we do something
VERY SILLY. We replace the labels with
the names of the Gregorian months. So,
replace the label CAPRICORN with the
label JANUARY so on.
8. Notice that for about two-thirds of
JANUARY the sun really is in CAPRICORN
so this silly sundial actually gives
the correct Gregorian month about 67%
of the year.
9. NOW for the clever bit. Without changing
ANY detail of the specification of the
Gregorian Calendar (which you clearly
want to keep) you follow the precedent
set by your hero Pope Gregory III. Just
once, you cut 10 days from the year. We
could do this anywhere but let's cut
10 days from March. JUST ONCE!
10. We now find the March Equinox is right
at the end of March so APRIL almost
exactly coincides with ARIES.
11. We find that each Gregorian month now
almost (but not quite) overlaps the
corresponding astronomical month.
12. This way, our 12 spaces really can be
labelled JANUARY to DECEMBER and the
sundial gives the correct Gregorian
month over 90% of the time.
This makes life MUCH EASIER for sundial
designers who want their sundials to tell
the date, at least approximately. It is
almost impossible to estimate the date
to better than two or three days close
to the solstices so this calendar would
be quite usable.
OK. Now for the bit you won't like...
The adjusted Gregorian Calendar is very
nearly the same as the Republican Calendar.
The main differences are:
1. They made every month 30 days.
2. They changed the rules for leap years.
The first change is not very important but
it is easier to teach children that EVERY
month is 30 days.
The second change IS important because, by
insisting that every year begins on the
day of the September equinox, you don't
get wild swings in the dates of the starts
of the atarts of the astronomical months.
With the current Gregorian Calendar, the
September Equinox can be on any of the
dates 21, 22, 23 and 24 September and that
is just at the longitude of France.
The Republican Calendar ensures that the
September Equinox is ALWAYS on the first
day of the first month of the year in
France. If you change longitude then
it will never drift more than a day
either side.
Suggestion:
Why don't you order one of these calendars
(English or Italian edition) then:
LIVE WITH IT FOR A YEAR and, this
time next year, you can tell us all
how you got on with it :-)
You might even enjoy the pictures and the
way the months work out.
As others have said: this calendar is
GREAT FUN.
Have a good year!
Frank
Frank King
Cambridge, U.K.
---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
