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Re: Julian Day Numbers [message #22561 is a reply to message #22430]

Tue, 14 November 2000 00:00

thompson
Messages: 584
Registered: August 1991

Senior Member

Ben Tupper <pemaquidriver@tidewater.net> writes:

> Hello,

> You may have heard the proverb, 'A person with two watches
> doesn't know what time it is.' It seems to be true for me.

> I have been tinkering with making tidal predictions which,
> of course, are dependent upon time. A number of benchmark
> dates
> are used to establish the phase difference for each harmonic
> component calculated. One of the benchmark dates is Noon,
> Jan 1, 1900.

> IDL> Print, JulDay(1,1,1900,12,0,0)
> 2415021.0

Using completely independent software, I can verify that this is correct.

> However, this is just in from a reliable source...

> * From the "Explanatory Supplement to the Astronomical
> Ephemeris" 1992, p.699
> * 1900 JAN 0.5 = JD 2415020.0.

This is also correct. The date-time you used in the first calculation would be
written as "1900 JAN 1.5". There is no discrepency here, only confusion about
the notation used in the Explanatory Supplement. I would have written the date
in the above quote as "1899 DEC 31.5"

William Thompson

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[Message index]

		Julian Day Numbers By: Ben Tupper on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Vapuser on Wed, 15 November 2000 00:00
		Re: Julian Day Numbers By: James Kuyper on Wed, 15 November 2000 00:00
		Re: Julian Day Numbers By: LC's No-Spam Newsread on Wed, 15 November 2000 00:00
		Re: Julian Day Numbers By: thompson on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Craig Markwardt on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Vapuser on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Craig Markwardt on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: davidf on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Ben Tupper on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: John-David T. Smith on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: Craig Markwardt on Tue, 14 November 2000 00:00
		Re: Julian Day Numbers By: davidf on Tue, 14 November 2000 00:00

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