Hi Fer, Ahh! That explains the single knife cut sundial then!! Thanks! So you hold the blade down, edge to the left and flat like the horizontal plane with your thumb up and along the polar axis then draw it toward you while rotating around your thumb as a fixed axis. Yep, that winds up being vertical at the 72 degrees west of south, just like it should be. ( here at 43.126 degrees North Latitude ) ( well, if you are right handed anyway. )
I never could understand the thumb tilt thing til I received this explanation. Original text --------------------------------------------------- > 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 sometimes 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]>; > <sundial@rrz.uni-koeln.de> > 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 > > > > > > > > > > -----------------------------------------------------Original text
