Dear Jos, Yes, great idea indeed and everything Chris Lusby Taylor says is correct except one thing:
> Timing the equinoxes is relatively easy... > Tough luck if that turns out to be during the > night! Don't be put off. You can time the instant of the equinox perfectly well even if it happens at night... What you do is note WHERE the centre of the shadow crosses a meridian line at NOON on the day of an equinox... You need a special mark on your meridian line showing where the shadow would cross if the equinox happens exactly at noon (very unlikely but it happens somewhere!). At the equinoxes, the declination of the sun changes almost exactly one arc-minute per hour. If you mark the meridian line with arc-minutes then, at noon, you can compare the instant of noon with the instant of the equinox. You can easily tell how many hours before or after noon the moment of the equinox was. You won't be far out if you do the measurement on the day before or the day after the equinox. The rate of change of declination is fairly constant over that period. There is a good example of exactly this kind of device in the Basilica di Santa Maria degli Angeli e dei Martiri in Rome. This was marked out by Francesco Bianchini in 1703. The great Italian diallist, Mario Catamo, calls the device Il Cronometro. With this, Bianchini could note the moment of the equinox to within a fraction of an hour. Good luck with your observations! Best wishes Frank King Cambridge, U.K. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
