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Re: day or night [message #82639 is a reply to message #82638]

Wed, 26 December 2012 22:21

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Gompie writes:

> I know the lat lon and time of a place on earth. How do I know if it is day or night.

Well, that's a good question. For which I don't have
a off-the-top-of-my-head answer, although I'm sure the
astronomers will and I'm reasonably sure the answer
is going to involve converting the time to a Julian time.

What does come immediately to mind, of course, is
my cgTerminatorMap program, which has to do something
reasonable similar.

http://www.idlcoyote.com/idldoc/cg/cgterminatormap.html

On about line 240 or so you see a number of calls to the "time"
functions of the Johns Hopkins University Applied Physics Lab.
I feel 100 percent certain that the answer to this question
is going to be found in the IDL routines that can be found
there:

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

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Re: day or night By: David Fanning on Thu, 27 December 2012 08:06
		Re: day or night By: Gompie on Thu, 27 December 2012 04:03
		Re: day or night By: David Fanning on Wed, 26 December 2012 22:52
		Re: day or night By: David Fanning on Wed, 26 December 2012 22:21

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