Over the years the kids have been getting me train calendars and I've kept them around for the great photos for each month. I have about a dozen now.
Then I got thinking: is there a formula to know in what year coming up that an old calendar would be accurate again and then I could use an older one again. It would be sort of a case, for example, where the 1998 would work in 2012 again. I am not trying to sound cheap here but was just wondering if there was a way that the next year the same calendar would be good again.
Just curious

Steamtown,
I don't remember the exact formula, but, if you think about it, January 1 can only fall on one of seven possible days.

Add the fact that leap years will double that number of possibilities for different calendars.

So look at the old calendar for the day that Jan 1 falls on, and check for a leap or non-leap February. That will tell you when it can be used again.

Jim

I believe the calander cycle is every 28 years for repeats. You can GOOGLE 'calander repeat' for many hits.

Well, according to my trusty, little, handy-dandy pocket Palm, January 1st fell on Tuesday, this year. The next time is in 2013 (5 years). The next time after that is 2019 (6 years). And the next time is 2030 (11 years).
So, there goes all theories and formulas right out the window.

the algorithm is called Zeller's Congruence...

http://en.wikipedia.org/wiki/Zeller's_congruence

Sorry... I may have responded too quickly.

ZC calculates the day of the week in any given year.

That is not exactly what you are asking, but it could be used to that end.

- Darren

Try GOOGLING perpetual calendar. I reuse my beautiful and pricey Ansel Admas calendars this way.

First thought is that it's every 28 years (7 days x 4 to cover leap years,) but there's a leap year correction for centuries -- the century must be divisible by 400. So the calendars will go out of phase in the year 2100. The up side for us is that none of us will be around to have screwed up calendars...unless my portrait from the Dorien Gray photo studio actually worked.

So long as you are not worried about where certain holidays fall...

There are only 14 different calendars that you need to own.

There are 7 non leap year calendars corresponding to the Jan first landing on a Sun to Sat.

There are 7 leap year calendars again corresponding to the Jan first landing on a Sun to Sat.

Predicting when a each calendar will come up is a bit more tricky. Its not a simple rotation of Calendar 1 to calendar 14 due to leap years.

For example 2006 began on a Sunday and ended on a Sunday.
2007 began on a Monday and ended on a Monday.
But 2008 began on a Tuesday and will end on Wednesday due to leap year
2009 will begin on a Thursday and end on Thursday and so on...

You will probably be able to collect 1 of each of the 7 non leap year calendars in about 10 or so years depending on how the leaps fall.

But it could take a lot longer (a minimum of 28 years!) to collect all 7 leap year calendars!

quote:

Originally posted by BillP:

But it could take a lot longer (a minimum of 28 years!) to collect all 7 leap year calendars!

Yes, but on the first of May one could change to a different calendar during a leap year.

Rand

 
  This is probably what you're looking for..........  

For years, in the white pages of the Pacific Bell telephone books there was a single page showing the 14 different calendars.

Each of the years from 1900 to 2025 had a number (1-14) corresponding to a calendar which was correct for that particular year.

Wish I'd have saved that page!!           I'm still searching (on the Internet) for it, though.  

That's how I knew I was born on a Wednesday!!         The next exact date will be                ... 2011 !!  

And the one after that         ... 2022 !!  

Gee, I wonder what model railroading will be like, then?  

 

I know a 1980 calendar will work for 2008, if that helps!

quote:

Originally posted by Smoke Stack Lightnin:

I know a 1980 calendar will work for 2008, if that helps!

... and for 2036, if you'd read the post above yours!  
 

quote:

Yes, but on the first of May one could change to a different calendar during a leap year.

Rand

Suggest that you change on the first of March.

Thanks for ideas and suggestions.
Not too scientific ... sort of a trial and error approach ......but:
If I can line Jan 1 to be on same day on years that do not divide by 4. I should be OK for whole year
and,
If I can line up March 1 on same day for years that can be divided by 4 I am OK

Actually Mar 1 on same day would work for rest of any years.

http://www.vpcalendar.net/Year_Correlations.html

OK, so here is a web page which shows you which calendar to use for every year!

Similar to the old chart in the phone book.

Here is another page on the same site that explains the numbering of calendars from 0 to 13 by first day of year and leaps...

http://www.vpcalendar.net/Weekdays.html