My so-called "Soda Can Dial," an inverted Sheperd's Dial, is corrected for the EOT, as well as for the longitude. It can be generated using the Macintosh version of my Sundials program, of which a WINTEL version is coming soon.
-----Original Message----- From: Debra Lopez & William Gottesman [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 30, 1999 11:29 PM To: peter ransom Cc: sundial@rrz.uni-koeln.de Subject: request re analemmatic dials Analemmatic dials do not correct for the equation of time, despite their name. Those which carry an image of the analemma along their center footprint might correct for the EOT at noon, but for the rest of the day. Good question about the shepards dial. It would be very easy to design a shepards dial that is already corrected for the equation of time, but to my knowledge, none are. The EOT does change each year, including leap years, and if you look at the dialist's companion program, you will note that there is a "mean" EOT for each 4 year cycle. I don't understand all of the factors which slowly change the EOT over time, but it may have something to do with the change of eccentricity of the earth's orbit. I have no idea whether precession of the equinoxes plays a role. Bill Gottesman Burlington, VT Message text written by "peter ransom" >Dear Reader, I would like to know whether the equation of time is used when an analemmatic dial is read. I have pictures of human analemmatic dials where the position of the gnomon is indicated by an analemma, and some where the position of the gnomon is indicated by dates on a central straight line. Both cannot be correct! My gut reaction is that the analemma takes care of the equation of time automatically, but would like confirmation of that, and whether the analemmatic dial with dates on the straight line need equation of time correction. Does one use the equation of time on a shepherd's dial? What happens to the e. of t. in a leap year? Should we have a new e. of t. each year? Thanks for your help. Carpe horam Peter Ransom<
