Warren et al, A simple way to show what a Babylonian hour is, is to rotate your horizontal plane ( for Bab. time 0 hours ) around a pole style and after each 15 degrees you have the plane for the next Babylonian hour. In reverse this may be used to see the Italian hours and the horizontal plane counts for It. 24.
The intersection of each plane with no matter what surface gives the appropriate B. or I. line on that surface. It is very nice to make a simple model to see how such a plane acts in space. BTW, the same principle may be done with a plane 66.5 degrees angled to a polestyle and you may see how the ecliptic circle moves in space relative to your horizon. Divide the ecliptic in 12 parts and you may see how each sign rises and sets. Such simple experiments are somtimes eye openers. 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: "Warren Thom" <[EMAIL PROTECTED]> To: "Steve Lelievre" <[EMAIL PROTECTED]>; <[email protected]> Sent: Saturday, January 12, 2002 2:17 PM Subject: Re: Acadian domestic sundials > Hi Steve, > > The answer is yes, to the question "can shadow plane dial be constructed to > show hours to sunset (Italian hours)?" You can think of the plane for one > hour before sunset as the horizontal surface 15° to your west (oops - or is > that east??) on the earth and at your latitude. A terrella would show this > plane nicely. Two hours is the horizontal surface 30° away. > > Maybe Mac Oglesby has caused me to think more in "planes" but the last issue > (December 2001) of the Compendium had some good articles on lines, planes > and surfaces. Steve Luecking had some very nice graphics showing "planes". > Gianni Ferrani describes the kalieidoscope cube that allows light only in > certain planes to pass through. Mac showed some student (hour plane) dials. > Fer had an article on polar bifilar. It helped me understand Fer when > Claude Hartman reported on the math work of Rafael Soler Gaya. I am still > digesting page 5 on how to calculate the lines and planes. > > Warren Thom ( 88W 42N) > > > Edley mentioned hearsay of a window dial, thus: > > > > "[The source] said they carved out deep narrow notches which, when the sun > > fully filled the notch, it was that particular time". > > > > That's sounds very much like a shadow-plane dial, but reversed to use > > illumination rather than shadow as the indicator. But according to the > > report, these dials were used to indicate time left before supper. This > > situation got me thinking - could a shadow plane dial be constructed in > such > > a way as to show time since sunrise / time to sunset? The descriptions > I've > > read, as I remember them, all relate to modern hour markings. > > > > Steve > > > > >
