Dear Mac, Fer de Vries has answered your question but he could be misinterpreted...
> Of course you are right that an Italian hour and a > Suntime hour aren't of the same length each day. > But we are talking about 30/24 second of time per > hour as maximum... This is true if you take 24 hours as the time between successive transits, but the difference can be MUCH greater if you take 24 hours as the time between successive sunsets... The maximum difference depends on your latitude. Where I am at 52 degrees north the difference can be nearly THREE minutes either side of 24 hours measured on a watch. A sundial CAN certainly notice that. At the equator, sunset is at 6pm (by the sun) every day so Italian hours don't change any more than astronomical hours. Inside the arctic circle things go mad! On some magic date (again depending on latitude) you experience a sunset that is the last you are going to have for some weeks or even months. Italian hours are not well defined then but, if you insist on deeming an Italian hour to be one 24th of the time between successive sunsets, then an Italian hour can last several days! In summary: Italian hours are rather boring in the Tropics and go mad near the poles. They are at their most interesting somewhere in between like, ahem, in Italy! I think it is most unlikely that, when the famous Italian explorer Umberto Nobile was making his expeditions to the Arctic, he used Italian hours! Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
