Hi Chris, The seasons are not well demonstrated on sundials with polar gnomons. These dials tune out the seasonal change to show equal hours. You need to go back to earlier concepts, dials using a vertical gnomon showing the length of the shadow, not the angle. Here are a couple of examples.
Declination lines: these lines trace the path of the sun's shadow from a point gnomon and show the solar position on the solstices, equinox or any day of interest in the year. The straight equinox lines are interesting. Then the shadow path is as straight line, west to east on a horizontal dial. In spring and summer the shadow path is a curve towards the gnomon. In the fall and winter, the long shadows are away from the gnomon. Seasonal markers. These points on analemmatic sundials tell you when and where the sun rises and sets throughout the year. Armillary spheres: Ptolemy's concept of a celestial sphere is what we observe in the heavens above. An armillary sphere is a great teaching tool showing the path of the sun on the celestial sphere. Sacrobasco's "De Sphera" was the astronomy text for many centuries. Perhaps we should translate it to "Johnny Hollywod's Balls" for the modern generation. The student's hand held armillaries on display in many museums where excellent teaching aids for visualizing the path of the sun, moon and planets across the star field of the observed celestial sphere. Italian and Babylonian hours; Our time is fix at high noon and midnight being 12:00, the start of a 12 hour cycle. Babylonian hours start at sunrise. Italian hours start and end at sunset. Noon moves with the season. These time systems were in common use except in north west Europe until the time of Napoleon. The seasonal change was much more evident using such systems. These are the solar seasonal time cycles that sundials show so well. They show real time. Regards, Roger Bailey www.walkingshadow.info ----- Original Message ----- From: "Chris Lusby Taylor" <[EMAIL PROTECTED]> To: "Hein" <[EMAIL PROTECTED]>; "'Ricardo Cernic'" <[EMAIL PROTECTED]>; "'lesliel'" <[EMAIL PROTECTED]> Cc: "'sundial'" <[EMAIL PROTECTED]> Sent: Saturday, March 22, 2008 3:48 AM Subject: Re: Welcome to summer; sundial display of seasons > "Hein" <[EMAIL PROTECTED]> added the thought that: > >> I like the longer daylight too. So I look up for the 30 of march, when >> daylight saving time (summertime) is beginning. >> Hein van Winkel >> 52 08 56 N 4 45 53E > > ..which reopens another can of worms, which I don't propose to deal with. > > But my daughter, just back from Singapore, was delighted to see snow this > morning. She hadn't seen it for years. So much for my claim that it is now > summer! > > I have been asked by the Meteorological Office to advise on a sundial > design, to go on their educational Web site, suitable for children to > make. > I've been trying to think how to show children about seasons through the > sun's movement. Clearly, a sundial can show you how the sun's altitude and > the length of day vary. Also, the amount of energy received from the sun > instantaneously/daily. Does anyone have any thoughts on how best to do > this, > or indeed other aspects of seasonality that a sundial can demonstrate? I'd > like to make it as relevant as possible to meteorology. > > Regards > Chris Lusby Taylor > 51.4N 1.3W > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
