Gregorian Calendar to Julian Day Number (JDN)

Not Reviewed
Equation / Last modified by MichaelBartmess on 2015/10/21 04:00
`"Day"_"(Julian)" = `
Gregorian Calendar to Julian Day Number (JDN)
Variable Instructions Datatype
Month Enter the month of the date to be converted Text
Day Enter the day of the date to be converted Integer
Year Enter the year of the date to be converted Integer
Rating
ID
MichaelBartmess.Gregorian Calendar to Julian Day Number (JDN)
UUID
94b6d3b7-7793-11e5-a3bb-bc764e2038f2

This equation gives you the Julian Day when you input a Gregorian (standard modern calendar date).

"The algorithm is valid at least for all positive Julian Day Numbers. The meaning of the variables are explained by the Computer Science Department of the University of Texas at San Antonio.

It is worth noting that this algorithm does not follow the NASA or the US Naval Observatory - the convention in these systems being that the Gregorian calendar did not exist before the date October 15, 1582 (Gregorian). This algorithm effectively back-dates the Gregorian calendar onto the Julian calendar for dates before the introduction of the Gregorian calendar. Thus any calculations made with this formula before October 15, 1582, will not agree with these previous ephemerides."1 

Example

If you input January 1, 2000, this equation will return the Julian Day:  2451545.0

See Also

References