This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by others.
The Lilian day number is similar to the Julian day number, except that
Lilian day number 1 started at midnight on the first day of the
Gregorian calendar, that is, 15 October 1582.
The Lilian day number is named after Aloysius Lilius mentioned in
section 2.2.
 
Continue to: