Byte Me by Marv Dealy
Recycle that Calendar
Tomb of Pope Gregory XIII commemorates the introduction of the calendar that bears his name.
I didn’t set out to collect calendars, really. Years ago I started buying an Ansel Adams photography calendar every year, and they were just too nice to throw away so I began collecting them. It wasn’t until some years had passed and the collection had grown to fill a good sized packing box that I discovered that I could reuse calendars.
That’s right, boys and girls, that calendar you just went through for 2009 will be good again in 2015, and no I don’t know whether that is pronounced “twenty fifteen” or “two thousand fifteen.” We’ll get to that another time.
For you collectors out there, dig into your steamer trunks and from the 1900s you can use any of the following years’ calendar for this brand new year of 2010: 1909, 1915, 1926, 1937, 1943, 1954, 1965, 1971, 1982, 1993, and 1999.
If your collection of calendars goes really way back, you’ll want to keep in mind that the switch over to the Gregorian Calendar from the Julian Calendar was in 1582, although that is not true for all countries. Some countries took centuries to adopt the new calendar, so if you’ve got an old calendar from one of those holdout countries, you’re on your own as to whether it’ll work in 2010 or not. Notably, Russia didn’t adopt the Gregorian Calendar until 1918, while Britain waited until 1752. To make it more interesting, some countries still use February 24 as a leap day when its needed, while the rest of us use February 29.
Wikipedia features a “permanent Gregorian Calendar” from October 15, 1582 to whenever, that you’re welcome to try to figure out (you’ll find it at tinyurl.com/y9v6rsk).
Those of you interested in more about the Gregorian Calendar can read more at Wikipedia or by Googling the phrase. The Wikipedia page I found is at tinyurl.com/bffwc and while there I read, “The Gregorian solar calendar is an arithmetical calendar. It counts days as the basic unit of time, grouping them into years of 365 or 366 days and repeats completely every 146,097 days, which fill 400 years, and which also happens to be 20,871 seven-day weeks. Of these 400 years, 303 (the ‘common years’) have 365 days, and 97 (the leap years) have 366 days. This gives an average year length of exactly 365.2425 days, or 365 days, 5 hours, 49 minutes and 12 seconds.”
I did a bit of searching around trying to find out why the calendar repeats and what the pattern might be, and found this Wikipedia page about the scary sounding “Doomsday algorithm” at tinyurl.com/pwujh which explained the repetition thusly: “There are 1 leap year and 3 common years for every weekday, the latter 6, 17 and 23 years after the former (so with intervals of 6, 11, 6, and 5 years; not evenly distributed because after 12 years the day is skipped in the sequence of Doomsdays). The same cycle applies for any given date from March 1 falling on a particular weekday.” Okay then.
When I went to look at the website where I found a virtual perpetual calendar years ago (vpcalendar.net), I discovered the frequencies in the “year correlations” page at the website showed that my 2010 calendar would be good again in 2021 (11 years), again in 2027 (6 years), again in 2038 (11 years), again in 2049 (11 years), 2055 (6 years), 2066 (11 years), 2077 (11 years), 2083 (6 years), and 2094 (11 years).
Back at the Wikipedia Doomsday date page I found the following which just confused me completely: “For any given date up to February 28 falling on a particular weekday, the 3 common years are 5, 11, and 22 years after the leap year, so with intervals of 5, 6, 11, and 6 years. Thus the cycle is the same, but with the 5-year interval after instead of before the leap year.
“Thus, for any date except February 29, the intervals between common years falling on a particular weekday are 6, 11, 11..”
At Yahoo Answers, I found a much simpler explanation (tinyurl.com/yzg8b6u) about calendars repeating, to wit: “If the calendar is not a leap year, the calendar will generally repeat itself 11 years later. If the calendar came immediately after a leap year, it will repeat itself only 6 years later.”
If you can figure that all out, you’re a better person than I, Charlie Brown. I just check the virtual calendar website once each January to see what to haul out of the trunk.
That is just about enough about calendars, except to say that you’re welcome to stop by my office and admire my 1993 calendars – it’s as far back as I could find in my collection and they’ll be on display for this entire year.
Email questions to Marv at: marv.dealy@throck.com.
Marv Dealy founded Throckmorten Enterprises in San Francisco in 1988 and moved the company to Big Oak Flat in 1996. Open Monday through Friday, 9-ish to 5-ish (209- 962-7308). The company provides technical support for a large Silicon Valley company’s webinars, as well as providing professional website design, and computer and network maintenance. The company also publishes the Yosemite Gazette.
