Hello Frans, I haven't seen a real example of such a dial but it is interesting to do some study with a model of it.
The date line indeed is longer then the minor axis of the ellipse. But it can be seen now that between the tropics the shadow will retrograde at some dates. For example a dial at latitude 20 degrees North. At the longest day the sun rises somewhere in the east, moves for some time to South as we at higher latitudes are used to, then the sun changes its direction and moves back in the Northern direction , passes North at noon, moves to Southern direction and later in the afternoon the sun changes its direction another time. Time reading may be difficult, because for some time the shadow line intersects the ellipse at 2 points and we don't know what point to use. Make a model on an inclining plane and try this. It is wonderful te see how the retrogradation acts. Best, Fer. Fer J. de Vries [EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: Frans W. MAES <[EMAIL PROTECTED]> To: Sundial List <[email protected]> Sent: Thursday, August 24, 2000 11:32 AM Subject: Analemmatic dial in the tropics? > Hi All, > > Following up on the discussion of shadow length in analemmatic > dials at low latitudes: > > Does anyone know of an analemmatic dial actually constructed in > the tropics, that is, between the tropics? In that case, the date line > should be longer than the minor (north-south) axis of the dial. > > Regards, Frans > > ===================================== > Frans W. Maes > Peize, The Netherlands > 53.1 N, 6.5 E > www.biol.rug.nl/maes/ > ===================================== >
