Converting Julian dates

[Kenneth Brody]

Ron Kracht wrote:
[...]
> 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

I think you mean <http://scienceworld.wolfram.com/astronomy/JulianDate.html>.

> called a Julian date because that method of dating was first proposed by
> Julius Scaliger in 1583.

I didn't realize that "Julian date" was not named after Julius Caesar, as
is the "Julian calendar".

> 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.

I've also seen "Julian date" mean "the day of the year" (ie: the epoch
is alway January 1st of the year in question -- as with the *nix date
command's "+%j" format), sometimes preceded by the year itself.  For
example, the OP's date of 3-Feb-2004 would be "2004034", for the 34th
day of 2004.

So, while "Julian date" may have a specific scientific meaning, the
general use of the term can mean any of several different things.

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| Kenneth J. Brody        | www.hvcomputer.com |                             |
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