Hi Robert,
<color><param>7F00,0000,0000</param>> > Charles Gann wrote: > > > > Ponder this one! > > > > On the calendar day of an equinox, from the moment that day first pops > > into existence somewhere on the earth, to the moment it winks out of > > existence, how long does it exist? > A given calendar > day, when measured in UT, starts at -12 hours when it is midnight in the > time zone immediately to the West of the IDL (for instance Kiribati) and > is already 12 hours old when the day starts at midnight in Greenwich. It > lasts until 24 + 12 hours UT when it finally becomes midnight in the time > zone immediately to the East of the IDL (for instance Samoa). So in > ordinary circumstances each (Gregorian) calendar day in fact lasts 48 > hours though during half of the time it is either a day earlier or later > somewhere else on the globe. </color>I think you are one hour off here. In the simple case of 24 time zones at 1 hour intervals, and an IDL between two of them, we have the following situation. Consider the time zone directly west of the IDL. Here a new day is born. Twenty-three hours later it is born in the time zone directly east of the IDL. There it lives for another 24 hours. So its life span is 47 hours, not 48. <color><param>7F00,0000,0000</param>> When Summer Time applies for countries bordering on the IDL, things get > even more complicated. During the summer months on the southern > hemisphere, the New Zealand Dependencies adopt a Summer Time arrangement > that puts them 12 hours 45 minutes ahead of Greenwich. During that period > a calendar day can thus last 48 hours and 45 minutes before it winks out > of existence on the globe. And this still not the longest possible day! > During the last winter, the island republic of Tonga adopted a time zone > 13 hours ahead of Greenwich to which they added another hour of 'Summer > Time', putting them 14 hours ahead of Greenwich. Thus the New Year's Day > of 2000 (erroneously claimed by the media world wide as being the first > day of the 3rd millennium) lasted from 10h UT on 31 December to 12h UT on > 2 January, or 50 hours in total. > </color>As it says on http://tycho.usno.navy.mil/tzones.html: "... nations are sovereign powers that can and do change their timekeeping systems as they see fit." Nevertheless, they link a map of world time zones: http://aa.usno.navy.mil/AA/faq/docs/world_tzones.html, as of July 1998. Time zones run from UT-12 to UT+14 there, which would make the life span of a day 26+24=50 hours. In case the UT+14 people choose to introduce DST, we even get at 51 hours for part of the year. With kind regards, Frans W. Maes Peize, The Netherlands 53.1 N, 6.5 E www.biol.rug.nl/maes/ =====================================
