Converting Julian dates

[Ron Kracht]

John Esak wrote:

>>>Sounds to me like this "Julian date" is simply a count of
>>>days, starting at 1-Jan-1900.  Add that number to
>>>"12/31/1899" and you get "02/03/2004".
>>>
>>>      
>>>
>>Thanks, that did it.
>>
>>Richard Kreiss
>>    
>>
>
>Sheesh, did what???
>
>The julian date I know about... is the number of days from the start of the
>year, any year.  As in
>
>   date +%j
>
>   for today gives 317
>
>Ken's question made most sense... what type of Julian value data are you
>talking about.  And what is this about 1-Jan-1900???
>
>John
>
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Technically a Julian date is the number of days since noon on January 1, 
4713 BC <http://scienceworld.wolfram.com/astronomy/BC.html>.  It's 
called a Julian date because that method of dating was first proposed by 
Julius Scaliger in 1583.  In the computer world it seems to mean the 
number of days since any commonly agreed upon epoch date - which is why 
Ken asked what kind of Julian date.  Since it is originally an 
astronomical calculation the time of day matters although for normal 
date calculations the time of day is generally assumed to be noon - 
resulting in whole number values when calculating the Julian date.