Re: What can be calculated with a sun dial?

[Bill Gottesman]

A few extra: The stereographic projection, as used by Oughtred, allows calculation of the sun's altitude and azimuth at any (day)time on any date, and conversely, the calculation for which date and time the sun is at a specific azimuth and altitude.  The stereographic and the orthographic (analemmatic dials) projections allow calculation of the time and azimuth of sunrise/sunset on any given date.  Capuchin altitude dials allow instant calculation of the time of sunrise/sunset at any given date (Alessandro Gunella showed how capuchin dials are derived from an orthographic projection in the NASS compendium, June 2008).  Some dials also calculate equal-hours.  Islamic dials have a Quibla line pointing to Mecca. And Hendrik Hollander's sundial pint glasses tell when to start drinking! I am curious to learn in what manner a sundial calculates the earth's eccentricity, aphelion and perihelion. -Bill On 11/16/2010 4:38 PM, Jos Kint wrote: Dear sun dialists,   What can be calculated with a good sun dial? Here is a list of 19 topics. Can you add some more items? 1. The hour of the day 2. The day of the year. 3. The solar altitude. 4. The solar azimuth. 5. The longitude of the sun dial. 6. The latitude of the sun dial. 7. The moment of the equinoxes 8. The moment of the solstices. 9. The length of the tropical year 10. The equation of time 11. The excentricity of the earth orbital around the sun. 12. The obliquity of the eclips 13. A compass function 14. The declination of the sun. 15. The moment of the perihelion 16. The moment of the aphelion 17. The moment of the next sun set 18. The Babylonic time 19. The Italian time     Jos Kint --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial

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