On Thu, Jan 20, 2011 at 12:29 PM, Brad Lufkin <bradley.luf...@gmail.com>wrote:
> I think having the JDN change at noon UTC avoids a lot of confusion. > Consider this: when is Thursday midnight? Is it the instant between > Wednesday and Thursday or the instant between Thursday and Friday? With the > current definition, it's crystal clear when the JDN changes: Thursday noon > is unambiguous. > Brad > > > On Thu, Jan 20, 2011 at 12:23 PM, Brent <bren...@verizon.net> wrote: > >> Napoleons' last orders to his troops at Waterloo: >> >> Napoleon: Alright men, listen up, we will attack precisely at 8 o'clock >> today. >> >> Private #1: You mean we will attack tonight in the dark? >> >> Napoleon: No, 8 o'clock tonight is actually tomorrow. >> >> Private #2: But it is already past 8 o'clock today. >> >> Napoleon: That's the old time, we are using Revolutionary time now. >> >> Private #3: Well my sundial says 8 o'clock today is 2 hours before >> midnight. >> >> Napoleon: Well that can't be right because then tomorrow would be today >> and today would be yesterday and we can't fight a battle yesterday. Maybe >> you are looking at your sundial upside down. >> >> Napoleon: Is everyone clear on the attack time now? >> >> The troops look at one another with raised eyebrows. >> >> Napoleon: Alright men, synchronize your sundials, may god be with you. >> >> brent >> >> Frank King wrote: >> >>> Dear Andrew (and Fer), >>> >>> Many thanks for this reference... >>> >>> http://www.aandc.org/research/nautical_time_and_date.html >>> >>> That is a splendid article and shows just what pitfalls >>> one can fall into when attempting to force historical >>> data to fit the present way of thinking! >>> >>> I share your thought... >>> >>> I can't really imagine that even sailors (or >>> astronomers) would have had the day changing >>> name at midday... >>> >>> That said, I have a feeling that when Italian Hours >>> were in common use in Italy both the date and the >>> day name changed at sunset. >>> >>> This is a cue for Italian readers of the list to >>> say that this has been widely discussed before >>> (which is true) and that no widespread agreement >>> has been established :-) >>> >>> One hang-over which still persists in astronomy is >>> the Julian Day Number which changes at noon UTC. >>> >>> As I write, it is Thursday and the JDN is 2455581. >>> In just over four hours time it will still be >>> Thursday but the JDN will be 2455582. >>> >>> The scope for confusion is almost endless. This >>> splendid list has now provided us with pictures >>> of one French Revolution Hours sundial with noon >>> shown as 10 and another with noon shown as 5. >>> Maybe Napoleon didn't write a rigorous spec? >>> >>> Frank >>> >>> >>> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >
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