Calendar faux meme – “every 823 years”

The year 2100 is NOT a leap year.

Several people I know IRL, intelligent people, have said they got a text or saw a Facebook message. It reads, e.g. “The month of December 2018 will have 5 Saturdays, 5 Sundays, and 5 Mondays. It only happens once every 823 years.”

When I first saw this meme a half decade or more ago, I knew instantly that it had to be untrue. The reason was that, as a kid, I devoured the World Almanac every year.

About a third of the way through was the calendar section, and it indicated that there were only 14 ways a calendar year could be constructed. January 1 starts on one of the seven days; it’s a leap year or it’s not. Seven times two is fourteen.

Perpetual calendar

In a non-leap year, if January 1 is on a Sunday, we had experienced that same pattern in 2006, 2017 and will again in 2023. Calendars repeat. 2018 looks just like 2007; 2029 and 2035 will be carbon copies.

(I’m talking calendar days, not moving holidays such as Easter or Yom Kippur.)

In general, a calendar will repeat every six or eleven years, depending on whether it hits one or two leap years in between. So 2002 is the model for 2013, 2019, 2030, 2041, 2047, et al.

Even leap years repeat, obviously less frequently. The calendars for 1992, 2020 and 2048 are the same.

One way to prove that the specific meme is a myth is to go to Time and Date for “When is Saturday the 1st?” Eliminating the months with less than 31 days:
May 2010; January 2011; October 2011; December 2012; March 2014; August 2015; October 2016; July 2017; December 2018; August 2020.

Basically I look at the perpetual calendar for 1801 to 2100 and see the repeating patterns.

Note, BTW, the year 2100 is NOT a leap year. “Any year evenly divisible by four is a leap year, except centesimal years (years ending in two zeros) which are considered common years and thus have the typical 365 days, unless they are evenly divisible by 400. Therefore, 1600 and 2000 are leap years, while 1700, 1800, 1900 and 2100 are not.”

For ABC Wednesday