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Julian Day NE Julian Day [message #93896]

Fri, 18 November 2016 04:30

andrewcool777
Messages: 27
Registered: November 2012

Junior Member

Hi All,

So in converting the time stamp from an astro image to Julian Day with JULDAY, I start off with seconds of 6.31, and after doing the back conversion with CALDAT, I end up with seconds of 6.3100353!

Is this to be expected? Is it "wrong?" Is it one of those weird digital precision
things that David F. used to bang on about? (Hi David)

IDL> print,!version
{ x86_64 Win32 Windows Microsoft Windows 8.5.1 Nov 14 2015 64 64}
IDL>
IDL> Jd = julday(10,1,2016,10,10,6.31)
IDL> print,jd,format='(F20.10)'
2457662.9236841439
IDL> caldat,jd,mon,d,y,h,m,s
% Compiled module: CALDAT.
IDL> print,y,mon,d,h,m,s
2016 10 1 10 10 6.3100353

And just to show that I'm calling the inbuilt IDL routines, and not altered copies:-
IDL> help,/source
Compiled Procedures:
$MAIN$
CALDAT C:\Program Files\Exelis\IDL85\lib\caldat.pro

Compiled Functions:
JULDAY C:\Program Files\Exelis\IDL85\lib\julday.pro

I'm puzzled. And a bit concerned.

TIA,

Andrew Cool

www.skippysky.com.au (for all your astro weather forecast needs...)

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[Message index]

		Julian Day NE Julian Day By: andrewcool777 on Fri, 18 November 2016 04:30
		Re: Julian Day NE Julian Day By: wlandsman on Fri, 18 November 2016 06:43

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