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Re: hours since 1-1-1 [message #45038 is a reply to message #44859]

Thu, 04 August 2005 06:51

R.Bauer
Messages: 1424
Registered: November 1998

Senior Member

kuyper@wizard.net wrote:

We prefer Julian Seconds which were initial defined by Ray Sterner at
JHUapl.

http://fermi.jhuapl.edu/s1r/idl/s1rlib/time/time.html

cheers

Reimar

> 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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