# CFLib.org – Common Function Library Project

## GetJulianDay([TheDate])

##### Last updated September 04, 2001

Version: 1 | Requires: CF5 | Library: DateLib

Description:
This function calculates the Julian Day for any date in the Gregorian calendar. Astronomers have used the Julian period to assign a unique number to every day since 1 January 4713 B.C.E. Julian Days begin at noon on the date specified.

Return Values:
Returns a numeric value.

Example:

``````<CFOUTPUT>Today's Julian Day is: #GetJulianDay()#</CFOUTPUT>
``````

Parameters:

Name Description Required
TheDate Date you want to return the Julian day for. No

Full UDF Source:

``````/**
* Calculates the Julian Day for any date in the Gregorian calendar.
*
* @param TheDate      Date you want to return the Julian day for.
* @return Returns a numeric value.
* @author Beau A.C. Harbin (bharbin@figleaf.com)
* @version 1, September 4, 2001
*/
function GetJulianDay(){
var date = Now();
var year = 0;
var month = 0;
var day = 0;
var hour = 0;
var minute = 0;
var second = 0;
var a = 0;
var y = 0;
var m = 0;
var JulianDay =0;
if(ArrayLen(Arguments))
date = Arguments[1];
// The Julian Day begins at noon so in order to calculate the date properly, one must subtract 12 hours
year = DatePart("yyyy", date);
month = DatePart("m", date);
day = DatePart("d", date);
hour = DatePart("h", date);
minute = DatePart("n", date);
second = DatePart("s", date);

a = (14-month) \ 12;
y = (year+4800) - a;
m = (month + (12*a)) - 3;

JD = (day + ((153*m+2) \ 5) + (y*365) + (y \ 4) - (y \ 100) + (y \ 400)) - 32045;
JDTime = NumberFormat(CreateTime(hour, minute, second), ".99999999");

JulianDay = JD + JDTime;

return JulianDay;
}
``````

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