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Re: hours since 1-1-1 [message #44859]

Tue, 26 July 2005 21:40

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

Mark Hadfield wrote:
...
> Anyway, IDL has the JULDAY function, which calculates time in Julian
> days, ie time since 12:00 hours on 1 Jan 4713BC. (OK, I withdraw my
> comment about 1 Jan 0001 being the silliest ever date-time origin.)

The epoch for the Julian Day system may seem silly, but it was
originally designed for use with ancient historical data. Its of
special interest to astronomers, who are interested in knowing exactly
how long ago an ancient astronomer observed a particular event. 4713 BC
is the year on which three different cycles associated with widely used
ancient calendar systems were all in sync. Of course, nobody was using
any of those calendar systems at that time, it's just a theoretical
connection based upon running those calendar systems backward until the
cycles are in sync. That synchronization makes it easier to calculate
the Julian day for each of those calendar systems, and therefore to
compare dates recorded in each of those systems with each other.

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[Message index]

		Re: hours since 1-1-1 By: James Kuyper on Tue, 26 July 2005 21:40
		Re: hours since 1-1-1 By: Mark Hadfield on Tue, 26 July 2005 20:00
		Re: hours since 1-1-1 By: Michael Wallace on Wed, 27 July 2005 14:32
		Re: hours since 1-1-1 By: R.Bauer on Thu, 04 August 2005 06:51

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