| Re: Julian Day Question [message #48873 is a reply to message #48872] |
Fri, 26 May 2006 07:20   |
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Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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David Fanning wrote:
> David Fanning writes:
>
>
>> Clearly, I am missing something important here. :-(
>
>
> Oh, wait! I am missing Mark's nice explanation of this
> problem on my very own web page. Sigh..
>
> http://www.dfanning.com/misc_tips/julianday.html
>
> But even after reading it, I'm very, very confused. :-(
Me too - it seems inconsistent.
The example on that page is:
IDL> print, julday(1,1,1,0,0,0), julday(1,1,1)
1721423.5 1721424
The *input* date, 0001-01-01, /should/ be based on how we define dates /now/, starting at
midnight. But the reference point for the input date seems to change (to 12noon) when the
hours/minutes/seconds are not supplied.
paulv
p.s. Mark's point (about using such a distant reference point for dates) is also a good
one. Why Julian and not, say, Gregorian dates? (At least for those of us that use the
Gregorian calendar). Another (somewhat) common reference I've encountered in satellite
data streams is the number of seconds since Jan 1, 1980, 00:00:00 - which makes more sense
to me that julian dates.
--
Paul van Delst Ride lots.
CIMSS @ NOAA/NCEP/EMC Eddy Merckx
Ph: (301)763-8000 x7748
Fax:(301)763-8545
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