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Re: IDL 5.4 label_date function [message #27791]

Wed, 07 November 2001 14:54

Wayne Landsman
Messages: 117
Registered: January 1997

Senior Member

> This would have made sense 2000 years ago when the date changed at midday,
> but these days it only makes sense to IDL developers.
>

Well, it also once made a small amount of sense to (non-solar) astronomers,
since starting at noon meant that telescope observations taken over one night
would all have the same integral value of Julian date (JD). Of course, this
is irrelevant for telescope observations from space , or for Australia/New
Zealand/Japan where noon UT (Greenwich time) occurs in the middle of the
night. So even astronomers now typically use modified Julian date (MJD)
defined as JD- 2400000.5 and which does begin at midnite.

Wayne Landsman landsman@mpb.gsfc.nasa.gov

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[Message index]

		Re: IDL 5.4 label_date function By: Wayne Landsman on Wed, 07 November 2001 14:54
		Re: IDL 5.4 label_date function By: Chad Bahrmann on Wed, 07 November 2001 14:37
		Re: IDL 5.4 label_date function By: Mark Hadfield on Wed, 07 November 2001 13:01
		Re: IDL 5.4 label_date function By: Mark Hadfield on Wed, 07 November 2001 12:45
		Re: IDL 5.4 label_date function By: Craig Markwardt on Wed, 07 November 2001 10:57
		Re: IDL 5.4 label_date function By: David Fanning on Wed, 07 November 2001 07:51

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