Test Message - please ignore
I think I've been excommunicated again. Recent messages to the SML weren't reflected back to me. Tonmy M. -
Re: difference between equinoxes and midsummer
Hello All, Willy Leenders wrote: Why (in the northern hemisphere) the time between spring equinox and summer solstice is about 1 day shorter than the time between summer solstice and autumn equinox ? Could it be said that the momentum gained from the Earth's "slingshot" around the sun carries it through the former period faster than the latter period, when the earth is just beginning to accelerate towards the sun again? Jim Tallman Artisan Industrials
Re: difference between equinoxes and midsummer
I received several reactions on my question. Thanks. Most of them gives answers to another question than mine. Only Andrew James gives an answer to my question. Maybe my question was formulated not clear. Therefore I re-formulate my question in a simple way: Why (in the northern hemisphere) the time between spring equinox and summer solstice is about 1 day shorter than the time between summer solstice and autumn equinox ? Willy Leenders Flanders in Belgium 50.9 N 5.4 E mailto:[EMAIL PROTECTED] -
RE: Sundial restoration
Manelic, Though I don't know the sundial work by J.FORT you asked for, I appreciate to draw your attention to the following book, also dealing with the restauration of painted sundials: "CADRANS DU SOLEIL" by Pierre Ricou/Jean-Marie Homet (Les cadrans peints des Alpes a la Mediterranee) Editions Jeanne Laffitte, 1984 ISBN 2-86276-087-0 Best regards, WIEL -Original Message-From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of MainsaSent: zaterdag 23 maart 2002 13:09To: sundial@rrz.uni-koeln.deSubject: Sundial restoration Dear friends, I know there is a sundial work by J. FORT entitled "Restauration de Cadrans Solaires peintes", in French language, but I do not know if it a book or an article. Can you to give me more data? I am interested in this work. Thank you very much. Best regards, Manelic
Re: difference between equinoxes and midsummer
Thank you Piero and John. But after your answers my problem remains. 1. The equation of time can explain no more than about 31 minutes. The difference I descirbe is 21 hours and 10 minutes. 2. I describe a difference between two parts of the elliptical orbit of the earth which are symmetrical with regard to the sun. It is not the difference between winter and to summer but the the difference between the time from spring equinox to midsummer on one hand and the time from midsummer to autumn equinox on the other hand. I look out for a further explanation. 1. The equation of time gives the difference between the sun time and standard time. Your difference is cumulative or integral of the daily difference. The orbital effect has a maximum difference of about 8 minutes (this does not include the inclination effect). Averaging this approximately sinusoidal variation over 6 months is approximately 7 minutes per day. 7 times 180 days = 21 hours. 2. As I and others have pointed out the closest approach to the sun (perihelion) and furthest distance (aphelion) are not symmetrical with the equinoxes which depend on the orientation of the Earth's axis of tilt to its orbit. Previous discussions of the equation of time in this list have indicated how these two system change with resect to each other over very long times, changing the shape of the equation of time. -- Cheers, John -
Re: difference between equinoxes and midsummer
In a message dated 3/26/2002 6:11:55 AM Eastern Standard Time, [EMAIL PROTECTED] writes: > 2. > I describe a difference between two parts of the elliptical orbit of the > earth > which are symmetrical with regard to the sun. It is not the difference > between > winter and to summer but the the difference between the time from spring > equinox to midsummer on one hand and the time from midsummer to autumn > equinox > on the other hand. > > I look out for a further explanation. > > Willy Leenders > Flanders in Belgium You are mistaken. The elliptical orbit is not symmetric from equinox to equinox. Between the fall equinox to the spring equinox, the earth reaches its closest point to the sun, and its orbit speeds up. Between the spring and fall equinox the earth reaches its farthest point from the sun, and the orbit slows down. Bill G. vermont -
RE: difference between equinoxes and midsummer
I think the difference may be explained by the axes of the ellipse of the Earth's orbit not coinciding with the equinoxes and solstices. In other words, as perihelion and aphelion are not at the solstices (as John wrote, January 4th not December 21st), the difference in speed of traversing the orbit can therefore account for the differences in the times from spring equinox to midsummer and from midsummer to autumn equinox. The equinoxes and solstices are governed mostly by the inclination of the Earth's axis in relation to the direction of movement round the orbit, and not much by the varying distance from the Sun. Andrew James -Original Message- From: Willy Leenders [mailto:[EMAIL PROTECTED] Sent: 26 March 2002 11:04 To: sundial@rrz.uni-koeln.de Subject: Re: difference between equinoxes and midsummer Thank you Piero and John. But after your answers my problem remains. 1. The equation of time can explain no more than about 31 minutes. The difference I descirbe is 21 hours and 10 minutes. 2. I describe a difference between two parts of the elliptical orbit of the earth which are symmetrical with regard to the sun. It is not the difference between winter and to summer but the the difference between the time from spring equinox to midsummer on one hand and the time from midsummer to autumn equinox on the other hand. I look out for a further explanation. Willy Leenders Flanders in Belgium 50.9 N 5.4 E mailto:[EMAIL PROTECTED] -
Re: difference between equinoxes and midsummer
Thank you Piero and John. But after your answers my problem remains. 1. The equation of time can explain no more than about 31 minutes. The difference I descirbe is 21 hours and 10 minutes. 2. I describe a difference between two parts of the elliptical orbit of the earth which are symmetrical with regard to the sun. It is not the difference between winter and to summer but the the difference between the time from spring equinox to midsummer on one hand and the time from midsummer to autumn equinox on the other hand. I look out for a further explanation. Willy Leenders Flanders in Belgium 50.9 N 5.4 E mailto:[EMAIL PROTECTED] john shepherd wrote: > >On Mon, 25 Mar 2002, Willy Leenders wrote: > > > >> The spring equinox was about at 3-20-2002 18:50 UT > >> Midsummer is about at 6-21-2002 13:10 UT > >> The autumn equinox is about at 9-23-2002 04:40 UT > >> The difference between the time from spring equinox to midsummer on one > >> hand and the time from midsummer to autumn equinox on the other hand is > >> about 21:10 hours. > >> > >> One should suppose there will be no difference in time between the > >> positions of the sun at declination 23.44 to 0 and between the > >> positions at declination 0 and -23.44. > >> > >> Can anyone give me an explication of this difference? > >> > > Willy Leenders, > > > >you found experimentally that seasons have not the same lenght!! You found > >also Equation-of-Time. Look at http://www.analemma.com/ > > > >My best regards > > > >Piero Ranfagni > > The equation of time contains two factors, one due to the inclination > of the Earths axis to the plane of its orbit and the other is due to > the variation in speed of the Earth in its orbit. See > http://www.uwrf.edu/sundial/Eqntime.html . The variation of speed > which is due to the elliptical nature of the Earth's orbit (Kepler's > Law of Areas) is the contribution which causes the effect Willy > Leenders describes. We are closest to the Sun on Jan 4th and hence > moving fastest, hence in the Northern hemisphere Winter is shorter > than Summer:-) > > -- > Emeritus Professor John P.G.Shepherd > Physics Department > University of Wisconsin-River Falls > 410 S. 3rd. St. > River Falls,WI 54022 > > Phone (715)-425-6203 > Fax (715)-425-0652 > - -
Re: Vitruvius or Oughtred?
Hi Anselmo, I think the essential difference between these two dials is that, for Vitruvius' spider dial, time is indicated by the shadow of the TIP of a vertical gnomon; Oughtred's Double Horizontal, on the other hand, uses the shadow of the vertical style EDGE. The curvilinear grids of hour angle vs. Sun's declination or altitude look superficially similar, but are to a different geometrical projections. Best regards, John Davis 51d 05m N: 1d 08m E -
