Hello Steve, Based on your discovery and to prove that from the vernal equinox to the autumnal equinox for a certain time to sunset the sun altitude is approximately equal, I made calculations and a graph showing that this is the case for 1, 2, 3 and 4 hours to sunset.
Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 6-nov-2017, om 02:15 heeft Steve Lelievre het volgende geschreven: > I have been doing some calculations for an Hours To Sunset dial (that is, an > Italian Hours dial with the numbering running backwards). I discovered that > the maximum altitude for a given hour does not occur at the summer solstice. > I was a little surprised to discover this - not amazed, but surprised enough > to make me wonder if I have done my calculations wrong. > > The attached diagram is for the example case of 4 hours before sunset. I'm > getting a double maximum occurring a little after the vernal equinox and a > little before before the autumnal equinox. I get similarly shaped curves for > others hours, with less separation between the peaks when I use higher > (italian) hour numbers. > Assuming that I have in fact graphed the altitude correctly, it means is that > there is a period over the summer months when the altitude for any given hour > to sunset stays approximately the same. In my case, at 49N, it seems that > over the summer months, the solar altitude for 1 hour to sunset is > approximately a little under 10 degrees, 2 hours to sunset is approximately a > little under 20 degrees, and so on at a little under 10 degrees per hour, at > least for the last 5 to 6 hours of the day. > In this day and age, I think we would demand greater accuracy, but have there > ever been sundials or other devices that exploited this approximation? > > Steve > <ejimonchepokegka.png> > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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