Αρκετές φορές μέσα από τα μαθήματα που κάνω για τον SQL Server όταν αναφέρω ότι το datetime έχει σαν βάση την 1/1/1753 οι μαθητές μου με ρωτάνε το λόγο.

Ο λόγος είναι ο εξής όπως τον εξηγεί όμορφα ο Tibor Karaszi

There are historical reasons for this limitation. In what we sometimes refer to as the "Western world," there have been two calendars in modern times: the Julian and Gregorian calendars. These calendars were a number of days apart (depending on which century you looked at), so when a culture that used the Julian calendar moved to the Gregorian calendar, it removed from 10 to 13 days. Great Britain made this shift in 1752. (So, in that year, September 2, 1752 was followed by September 14, 1752.)

An educated guess as to why Sybase SQL Server—the predecessor of Microsoft SQL Server—selected 1753 as the earliest date is that if you were to store a date earlier than 1753, you would also have to know which country was using which calendar and also handle this 10- to 13-day jump. So Sybase decided to not allow dates earlier than 1753. Note, too, that other countries made the shift later than 1752. Turkey, for instance, did it in 1927.

Being Swedish, I find it amusing that Sweden had the weirdest implementation. Sweden originally planned to skip every February 29, leap day, over a period of 40 years (from 1700 to 1740) so that Sweden would be in sync with the Gregorian calendar after 1740 (but meanwhile not in sync with anyone else). However, in 1704 and 1708 the leap day wasn't skipped for some reason, so in 1712 (which was a leap year), Sweden inserted yet one more extra day (imagine being born in Feb 30!) and then made the shift over a day, in 1753, in a similar manner to everyone else.

By Tibor Karaszi, SQL Server MVP