Hi All,
This reminds me of a sundial, made by Landscape artist Paul de Kort in Zaanstad/The Netherlands. For dialing usually the zodiac-signs are defined as 30 degrees of the ecliptica. However, the true sun will pass the 12 constellations of the zodiac and also the constellation Ophiuchus (dutch: 'slangedrager'). Paul did make a sundial in which this 13th 'zodiac'-constellation is incorporated. Very nice. for more work of Paul see: www.pauldekort.nl for the sundial, see (page 6): http://www.pauldekort.nl/_backgrounds/getijdenpark%20BROCHURE%20lowres.pdf kind regards, Hendrik Hollander -------------------------- Analemma zonnewijzers Hendrik Hollander tel: 020 637 43 83 mob: 06 16 462 879 www.analemma.nl www.linkedin.com/in/hendrikhollander -------------------------- lees de disclaimer: www.analemma.nl/maildisclaimer.htm -------------------------- ----- Original Message ----- From: "Bill Gottesman" <billgottes...@comcast.net> To: <sundial@uni-koeln.de> Sent: Tuesday, December 22, 2009 4:51 PM Subject: Re: zodiac lengths Well done, Frank! -Bill Gottesman Frank King wrote: > Dear Thomas, > > You ask interesting questions and the > answers depend slightly on just how > precisely you want the model the way > the sun goes round the ecliptic. > > QUESTION 1 > > ... do [Gemini and Cancer] share > *exactly* the same region [on a > sundial] or not? > > I think it is reasonable to DEFINE > the 12 regions of the Zodiac as being > bounded at 30-degree intervals of > solar *longitude*. So Aries extends > from 0 to 30 and so on. > > On the ecliptic, these 12 regions are > distinct and there is no sharing. > > When you look at the corresponding > intervals of solar *declination* > you do, as you say, get sharing. > > In your example: > > Sign Longitude Declination > range range > > Gemini 60 to 90 20.15 to 23.44 > > Cancer 90 to 120 23.44 to 20.15 > > As you see, Gemini and Cancer share the > same range of declinations but for Gemini > the declination is increasing and for > Cancer is decreasing. > > The answer to your question is YES. > > So far, this theory has nothing to do with > the *shape* of the Earth's orbit but it does > assume that the orbit is a plane which is > isn't exactly. > > [Solar latitude hovers around zero but it > isn't exactly zero. A REALLY pedantic > discussion about whether Gemini and Cancer > exactly overlap would take a book!] > > You then ask about dates. That makes the > story very much more complicated but it > doesn't stop Gemini and Cancer sharing > the same region on a sundial. > > QUESTION 2 > > Is the starting date May 20 of one in line > with the end-date July 22 of the other or not? > > You go too fast. Who says the starting date > is May 20? It sometimes is and it sometimes > isn't. You have to worry about the leap-year > cycle and Pope Gregory XIII and his friends. > > At the moment we are living close to the middle > of an almost 200-year run of pure Julian > calendar. There are no omitted leap-years > between 1904 and 2096 inclusive. This means > there is a steady drift in all the dates you > are interested in. > > The starting *declination* of one IS in line > with the ending *declination* of the other but > when you worry about dates everything becomes > harder. > > The only sensible answer to this second > question is NO. It is no because the dates > change from year to year. See the answer > to Question 4, but first... > > QUESTION 3 > > The angles of the ecliptic longitude for > the zodiacs are equally distributed (each 30°), > [YES that's right] but what about the angles > in the earth's orbit around the sun (ellipse)? > > I don't quite understand this. The ecliptic > longitude is the same as the angle of the Earth's > orbit round the sun (though you might want to > change the sign or add 180 degrees). > > The answer is THEY ARE THE SAME. > > QUESTION 4 > > And what about the dates? > > They are horrible! I have already said there is > a steady drift in the dates but it is worse than > that because of the precession of the equinoxes. > The answer is THE DATES ARE A MESS and... > > QUESTION 5 > > The lengths (in terms of time) of the zodiacs > are not equal, but are they constant each year? > > The answer is UNFORTUNATELY NO. It is easy to > see that they are not constant by thinking about > this time of year. We have just entered the > sign of Capricorn and at this time of year the > Earth is closest to the sun. > > That's good news because it gets winter over > quicker. Capricorn doesn't last long! Also, > this explains why the lengths are not constant. > > Unfortunately, there will come a time when we > are furthest from the sun in winter. Capricorn > will take longer and we could find the northern > hemisphere covered in ice. > > [ There will then be conferences about trying to > raise the levels of carbon dioxide :-) ] > > QUESTION 6 > > Can anybody give me a better reference than > Wikipedia... > > The best thing you can do is to ask your girlfriend > to buy you a copy of "Astronomical Algorithms" by > Jean Meeus as a Christmas present. You can then > write a proper program to model the Earth-Sun > system. It took me about 2000 lines of code before > I was happy with it but it is a very good way of > answering your questions! > > Best wishes > > Frank > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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