Calendars

[kriskwery]

I am in the process of replacing 2011's calendars around the house with those for 2012. Is there an easy way of telling when the same configuration of days/dates in a year will recur? I have quite a stash of previous years' calendars (sad, innit?!) but, at 64 years old, I wonder what the cycle is and whether I'll be alive to re-use any of them.

[Buenchico]

Sorry, it's not easy!
Consider when 1st January is this year, and in future years:

In 2012 it's a Sunday.
It's a leap year this year, so 1st January will be two days of the week ahead next year (instead of the usual one). i.e. in 2013 it's on a Tuesday.
For the next 3 years it will move one day forward:
2014 Wednesday
2015 Thursday
2016 Friday
Since 2016 is a leap year, it will then jump 2 days again:
2017 Sunday

So a calendar for 2012 would, at first glance, appear to be valid for 2017 (as the year starts on a Sunday again). However the calendar only stays the same until the end of February, because 2012 is a leap year but 2017 isn't. This year's calendar can't be re-used until 2040!
http://en.wikipedia.o...ar_starting_on_Sunday

The easiest way to work out when your calendars will be valid again is to Google for the relevant Wikipedia pages, remembering to take into account whether your calendar is for a leap year or a common (= 'non-leap') year.

For example 2011 was a common year starting on a Saturday. Enter 'common year starting on Saturday' into Google and you'll be led to this:
http://en.wikipedia.o..._starting_on_Saturday
Looking at the 'Gregorian' list (because that's the type of calendar we use these days), you'll see that you can re-use your calendar in 2022.

Chris

[Jonathan-Joe]

The calendar repeats, in every respect, over a cycle of 28 years, until we reach a year ending "00". That is because that year, although divisible by 4, is not a leap year. (It' unlikely that yyou will reach this point!)

The actual cycle is best expressed as the day of the week on which January 1st falls. We move one day forward each year, until we pass a leap year, when we move two.
Starting at 2012 - M(L), W, Th, F, Sa(L), M, Tu, W Th(L), Sa, Su, M, Tu and so on.
So is it worth keeping 27 calendars in store?

[New Judge]

Just one point of pedantry, Jonathon, a year ending in "00" IS a leap year if it is divisible by 400. Hence the year 2000 was a Leap Year, but 1900 was not.

[Jonathan-Joe]

Judge, yes, you're right, though none of us will see that again!
Where I am wrong is in saying you need 28 calendars. Of course, you don't, as some are used more than once in the 28 year cycle. You need 14 calendars - 7 with !st Jan on M, Tu, W, h, F, Sa and Su for ordinary years ans another 7 for the leap years.

[theprof]

This is a job for that mighty annual reference source, Whitaker's Almanack. Mine cost me £50.00 yesterday but you can check the book at most reference libraries.

the section you want is called "Calendar for any year 1780-2040" and begins on pages 1296 in the 2012 edition.

The 2011 calendar next occurs in 2022, then 2033 and finally 2039. I wouldn't bother keeping the 2012 calendars as it next occurs in 2040! If you have any other specific years that you want to know about, let me know.

I'm afraid that the 28 year cycle repeat referred to by Jonathan-Joe is not supported by Whitaker as can be seen from the 2011 calendar provided above, although 2012 works. The 1990 calendar has been repeated in 2001 and 2007 and will repeat again in 2018, 2029 and 2035.

i'm afrai

[theprof]

Oops, scrub those last couple of words!

[kriskwery]

Better still, now I've used a search engine with a good choice of words (calendar for any year!), I've found a solution, I think (though not tested it yet!):
http://www.hcidata.info/cgi-bin/calendar.cgi

[mibn2cweus]

To have a calendar for every month you'd need to amass a collection of 91 different monthly calendars whereas you only need a collection of 14 different annual calendars for any year in the foreseeable future . . . go figure!

Either way, I wouldn't count on the date specified for Easter - http://www.assa.org.au/edm.html

[Old_Geezer]

I'd just open MS Outlook and scan through until I saw what I was looking for. Try to match each year with a calendar you already have.