Hello Jos, Frank and all,One of the things that I learned from Frank King at a BSS meeting was the date of the spring equinox and its importance in history. He showed a "blob chart" similar to the attached chart, "Equinox.pdf". This clearly showed the need for leap years and the Gregorian correction to the Julian calendar. He also showed a much better calendar based on cycles of four and 33 years. This calendar fixed the spring equinox to a 24 hour period over thousands of years. At one longitude, the spring equinox would always be on one date, one 24 hour period with this calendar. This longitude, sometimes called "God's Longitude", happens to be 77° west, Washington DC.
Thanks Frank for that inspiring BSS presentation. I took the idea a bit further and co-authored a presentation with Fred Sawyer called "God's Longitude and the Lost Colony of Virginia" for the NASS conference in Virginia in 2007. This presentation is on my website "www.walkingshadow.info" #7 on the list of publications.
The fall equinox this year is 23 Sept at 09:04 UTC. That is just 4 minutes local time into 23 Sept where I live.
Regards, Roger Bailey N 48.6, W 123.4 -------------------------------------------------- From: "Frank King" <[email protected]> Sent: Thursday, September 22, 2011 3:00 AM To: "Jos Kint" <[email protected]> Cc: <[email protected]> Subject: Re: Leap year
Dear Jos, You ask a good question...Can a sundial be used to see if we are in a leap year or not?You need to come to the British Sundial Society Newbury meeting on Saturday. I shall be giving a talk entitled: Mind the Gap: Sundials and Leap Years Visit the BSS website http://www.sundialsoc.org.uk and then download: http://www.sundialsoc.org.uk/Download/2011-Newbury-Leaflet.doc ...to find details of the time and place of the meeting. If you can't slip over from Belgium then you can read an article on the subject that I hope will be published in the December BSS Bulletin. The short answer to your question is "yes" but the limitations of the Gregorian Calendar mean you can't satisfactorily design an instrument without moving parts that will track the leap year cycle for more than about 40 years. You can look at the attached picture where you can see the analemma I set out in London where 29 February is included as a separate date. How about joining the BSS? You will find the answers to many of your questions there :-) All the best Frank King Cambridge, U.K.
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Equinox.pdf
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