Dear Mark, I may be completely off the point with the following remark, as I do not have the book you cited. So I am just guessing what "y" you are talking about. However I do possess the "Gnomonique Moderne" by Denis Savoie and I checked the section on vertical dials there. The 1997 edition gives you on page 81 the coordinates for the center of the dial.
The equation for y(0)= a. tan(phi) / cos(D) (a= height of the gnomon, phi= latitude of location, D= declination of wall). Would tan(phi) in the numerator also have to be exchanged for tan(delta) ? (delta= declination of the sun) I may try to verify in the next days. Günther Faltlhansl [EMAIL PROTECTED] ----- Original Message ----- From: "Mark Gingrich" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, November 27, 2000 7:14 PM Subject: Sundial Formula Erratum in Meeus's Book > Dial folk, > > Those who rely on the sundial formulae in the second edition (1998) > of Jean Meeus's book _Astronomical Algorithms_ should be aware of > the following erratum: On page 406, in the chapter titled "Calculation > of a Planar Sundial", by R. Sagot and D. Savoie, in subsection (3) on > vertical sundials, the third equation, the one for "y", should have > a "tan delta" in the numerator, not a "tan phi" as is shown. > > This error does *not* occur in the first edition (1991). > > I've already brought this issue to Jean Meeus's attention. He replied > today with the following e-mail, which lists two other typographical > errors in the second edition. Owners of this later edition should make > the necessary corrections to their copies. > > > > Date: Mon, 27 Nov 2000 10:01:05 -0500 > > From: Jean Meeus > > Subject: Erratum in Astronomical Algorithms, 2nd Ed. > > To: Mark Gingrich <[EMAIL PROTECTED]> > > > > Thank you for mentioning that typographical error. It is my own fault : > > the error didn't appear in the first edition of the book. > > > > Here are two other typographical errors in the book : > > > > (1) Page 63 : If Z is equal to or larger than 2299161 (same constant as > > on the previous line), not 2291161. > > > > (2) Page 144, fifth line from the bottom : the double negative sign should > > be a single one. > > > > Thanks and best regards. > > > > Jean Meeus > > > ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ > Mark Gingrich [EMAIL PROTECTED] San Leandro, California >
