Proleptic calendars

[John Cowan]

Here's another specific reference, from
http://www.magnet.ch/serendipity/hermetic/cal_stud/cal_art.htm#Proleptic

# Every date recorded in history prior to October 15, 1582 (Gregorian), # such as the coronation of Charlemagne as Holy Roman Emperor on
# Christmas day in the year 800, is a date in the Julian Calendar, since
# on those dates the Gregorian Calendar had not yet been invented.

# We can, however, identify particular days prior to October 15, 1582
# (Gregorian), by means of dates in the Gregorian Calendar simply by
# projecting the Gregorian dating system back beyond the time of its
# implementation.  A calendar obtained by extension earlier in time
# than its invention or implementation is called the "proleptic"
# version of the calendar, and thus we obtain the Proleptic Gregorian
# Calendar. The Julian Calendar also can be extended backward as the
# Proleptic Julian Calendar.

# For example, even though the Gregorian Calendar was implemented on
# October 15, 1582 (Gregorian) we can still say that the date of the
# day one year before was October 15, 1581 (Gregorian), even though
# people alive on that day would have said that the date was October 5,
# 1581 (the Julian date at that time). As another example, the date
# of the coronation of Charlemagne, December 25, 800, in the Julian
# Calendar, was December 29, 800, in the Proleptic Gregorian Calendar.

-- 
John Cowan	http://www.ccil.org/~cowan		cowan at ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)