Michael Portwood

The Amazing Disappearing Days

The UNIX cal command takes into account events like leap year. For instance, if you want a calendar for August 2010 or February 2012, the UNIX cal command will produce the correct results.

Let’s try an experiment. Execute the following UNIX/LINUX command.

cal 9 1752

The output looks like…

Days 3-13 are gone! What happened to those 11 days?

Explanation

The modern calendar is a compilation of many usages dating from the days of Julius Caesar, when the Greek astronomer and mathematician Sosigenes devised a calendar for Rome that is essentially the one that is familiar to us as our present-day calendar. It was during the late 16th century that work of the 6th century Anglo-Saxon monk, Bede, was submitted to Pope Gregory XIII who accepted the calculations and made the decision to issue a more accurate calendar that ultimately was accepted. Most Roman Catholic countries adopted the Gregorian calendar. Many Protestant countries did not accept the new calendar until the 18th century, including Great Britain, which meant America as well.

Great Britain and all its possessions finally accepted the Gregorian calendar effective March 25, 1752. But, a remarkable 2-step change was required. It is important to understand that the British used to change the year number on March 25th and not January 1st as we do today. On March 24, 1751 the next day would be March 25, 1752 advancing the year as usual.

A somewhat confusing phenomenon occurred.

First, it was decreed that 1752 should end with December 31st and not be carried on to the next March 25th.

For the sake of clarity, the period of January 1 - March 24, 1751 was the end of an epoch. The year of 1752 began on March 25th and ended with December 31, 1752, thus the earlier days of 1752 never existed, as the deleted days of September 3-13 also never existed. The year 1752 was a very short year; 72 days, in fact.

Of course, dates may be recomputed from the old to the new calendars. For instance, George Washington's birthday was February 11, 1731 as far as his mother was concerned. Today, we must reckon his birthday as February 22, 1732 in consideration of the new calendar. To put it in perspective, if we count backward from today the actual number of days since Washington was born, we would come up with February 22, 1732 using the present-day calendar.

To convert from the old Julian to the new Gregorian calendar, one must add 10 to 13 days to the old date, and sometimes change the year when the date considered falls within the period January 1-March 24. This is crucially important to those interested in genealogy and historical research. Documented dates before March 25, 1752 do not necessarily always correlate with a stated period of time. References to any New Year's Day before 1752, in Great Britain, meant March 25th.

Second, it was also decreed that the arrival of September 3, 1752 should be called September 14, 1752. This should be Wednesday September 2, 1752 was followed by Thursday September 14. September 2 existed; September 3-13 (11 days) did not; September 14 existed.

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