OMG Issue No: 16681
Title: Gregorian Calendar Introduction
Andrew Watson – OMG – email@example.com
(This comment came from the Architecture Board's review of the final submission.)
On p100 it is stated that "the Gregorian Calendar was introduced in
1582" and corrected calendar drift by "skipping over the dates between
October 5-15, 1582". This is true, but it's worth noting that only Spain, Portugal, the Polish-Lithuanian Commonwealth, and parts of Italy implemented the new calendar on Friday 15 October 1582 (following Julian Thursday 4 October 1582). Other countries stayed with the Julian calendar, so those "lost dates" (e.g. 10th October 1582) are valid in those countries. France adopted the Gregorian calendar on Monday 20 December 1582 (following Sunday 9 December 1582). Other countries followed over the centuries, with the UK and East-Coast American colonies not switching until 1752 (Wednesday 2 September 1752 was followed by Thursday 14 September 1752). Russia didn't change until 1918. The last countries to change seems to have been Greece, where Thursday 1 March 1923 followed Wednesday 15 February 1923, and Turkey, which switched in 1926.
(Yes, I got all those dates from Wikipedia :-).
Hence I think this section would benefit from a comment saying that although the Gregorian Calendar begins in 1582, various countries switched on various later dates, so that to be completely unambiguous, dates after October 1582 should really state which calendar they use. (For instance, today, Sunday 11th September 2011 in the Gregorian Calendar is Monday 29th August 2011 in the Julian calendar).
Similarly, at the top of page 121 it says that the Gregorian calendar was "introduced in 1582". It might be more accurate to say it was "first defined" in 1582 (or some similar wording), and "introduced" in different countries at different later dates.
Remove the extraneous text under ‘nominal time unit’ that discusses the history of the Gregorian Calendar.
Add Notes to the definition of ‘Gregorian Calendar’ explaining when this calendar was adopted in various countries, and cautioning that some historical dates may not use this calendar.
In clause 9.1.1, DELETE this sentence from the end of the Note under ‘nominal time unit’: “The Gregorian calendar, introduced in 1582, refined the Julian calendar, which had an accumulated drift of 10 days at that time (over a time interval of 1628 years), which was corrected by skipping over the dates between October 5-15, 1582 [Inter Gravissimas].” Change the reference from ‘leap years’ to ‘leap days’. The Note should read:
Each nominal time unit can be traced to counting cycles of some natural phenomenon. Historically the phenomena have been astronomical: the orbital cycles of the Earth and the Moon and the diurnal cycle of the Earth. Unfortunately for time keeping, these cycles are incommensurable, requiring intercalary time periods to maintain synchronization. Leap days have been used since 46 BC with the introduction of the Julian calendar to keep the calendar aligned with seasons of the year.
In clause 9.5.5, ADD two notes to the end of the glossary entry for ‘Gregorian Calendar’:
The Gregorian Calendar was defined in 1582 in [Inter Gravissimas], and was adopted at various times by various countries. It is now the international standard calendar.
The interpretation of any date depends upon the calendar used. Caution should be used with historical dates because the standard calendar varied by locality as well as time. The Gregorian Calendar was adopted in 1582 in Italy and a few other countries, and at various times as late as 1926 in in other countries.