Hello Mashallah and all, Your question on the exact time of the vernal equinox is excellent. The usual answer to the question on the date of the vernal equinox is "21st March". But it will not be the 21st of March for the next the next century, specifically 2102. With the Gregorian calendar, the date varies over 4 days, 19 to 22 March. The Iranian calendar is much more accurate as it is routinely reset by the actual astronomical event. The precursor to the current Iranian calendar was proposed by Omar Khayyam, the famous Persian poet, philosopher and astronomer. His calendar based on a 33 year cycle for leap years resulted in the vernal equinox always being with in a 24 hour period. At one longitude, 77ยบ W, the vernal equinox would always be the same date. This meridian has been called "God's Longitude" and the search for the perfect calendar and God's Latitude has affect the history of colonization in America.
Fred Sawyer presented our research on this topic at the NASS conference in August in Virginia. A copy of the presentation "God's Longitude" was included as a digital bonus with the latest copy of the NASS Compendium. It available to download for those interested at http://www3.telus.net/public/rtbailey/GodsLongitude as a 7.5 MB PowerPoint file, God Longitude.ppt. I encourage you to download the presentation as it outlines in detail the fascinating intrigue at the time of the Gregorian calendar reform. and the difficulty in answering your question on the time of the vernal equinox. The question of the exact time of the vernal equinox is addressed in a paper "The History of the Tropical Year" by Jean Meeus and Denis Savoie in the Journal of the British Astronomy Association JBAA 102, 1, 1992. Using an implementation of Meeus Algorithm, Luke Colleti's sun calculator at http://www.gcstudio.com/suncalc.html gives 03/20/05:49:31. The US Naval Observatory at http://aa.usno.navy.mil/data/docs/EarthSeasons.php gives 03/20/05:48. The Royal Astronomical Society of Canada (RASC) Observers Handbook 2008 gives: 03/20/5:49. As you can see it is difficult to predict the time to the minute and second. The story of "God's Longitude" is based on research by Simon Cassidy, well described in Duncan Steel's book "Marking Time: The Quest for of the Perfect Calendar". Fran King's presentation on this topic at the BSS meeting in Cambridge this year sparked my interest in the topic. Regards, Roger Bailey www.walkingshadow.info 1.----- Original Message ----- From: Mashallah Ali-Ahyaie To: [email protected] Sent: Thursday, December 13, 2007 6:30 AM Subject: Equation of Time Booklet and Calendar - 2008 / Re: sundial Digest,Vol 24, Issue 6 I wonder whether you could help from where one can get the same data for the exact time of the vernal equinox, in March 2008, but with the most possible precision; to the fractions of seconds (time and degree.) This is the exact moment on which the Iranian calendar is based on, as a starting point, but the timing has to be very precise. For the Iranian calendar the exact quantity of EOT, to the most possible precision is required too. Mashallah Ali-Ahyaie
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