Dear Jack, You go straight to the heart of the matter...
> I was struck by the fact that the Italian and > Babylonian hours coincide (cross each other) > at the equinox line but not at the solstice > lines. It is, of course, these criss-crosses which make having the Babylonian+Italian hour-lines so appealing. You are right that you don't get crossings at the solstices but you DO get crossings at EIGHT other declinations besides the equinox. If sunrise is a half-integer number of hours before or after 6am then, during the day, the shadow of the nodus will trace a path through a sequence of crossing points. At each such point both the Babylonian hour and the Italian hour is an integer. This is in the latitude of Cambridge. In theory, it means there are 18 days a year when the trace goes through crossing points. In practice this doesn't happen at an equinox because the declination doesn't stick at zero all day! The extreme declinations are when the sun rises two hours before or after 6am. At you go towards the equator the number of declinations where you get this effect reduces. If you really want crossing points at the solstices, then you need to move to a latitude where sunrise, at the solstices, is a half-integer number of hours before or after 6am. I rather fancy Babylonian hours myself. I could happily get up every day at 0h Babylonian and accept that sunset may be anything from 7.5 hours to 16.5 hours later where I live. I think this means joining a rather exclusive Religious Order! All the best Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
