Concerning the question of when the analemma, which I interpret to be equivalent to the equation of time, was discovered and how: We think of the equation of time as expressing the relationship between the position of the sun and "real time", but there is also a direct astronomical interpretation. The sun and the stars move relative to each other at an almost uniform rate. The equation of time describes the nonuniformities of this relative motion, irrespective of whether the stars or the sun or neither moves uniformly in real time. This could have been discovered by any good astronomer in ancient times, say in Babylonia. A clock good enough to compare daytime observations of the sun with nighttime observations of the stars would be a great help, though not absolutely essential. A clock good enough to compare observations of the sun made months apart would not be necessary until you want to know who's "right", the stars or the sun. I suspect the quality of clock needed to answer this question is similar to the quality needed to find the longitude.
Art Carlson -- To study, to finish, to publish. -- Benjamin Franklin Dr. Arthur Carlson Max Planck Institute for Plasma Physics Garching, Germany [EMAIL PROTECTED] http://www.rzg.mpg.de/~awc/home.html As usual, if I am caught or killed, the Institute will disavow any knowledge of my actions.
