On Tue, Sep 20, 2022 at 4:44 AM Frank King <[email protected]> wrote:
> 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. > > >
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