alexpgp | What people won't believe!

I just saw a curious quasi-chain-letter post on a Facebook page belonging to someone who ought to know better. (I define a "quasi-chain-letter" as something that asks you to repost, instead of the more traditional "send money," although the requisite "bad things will happen otherwise" is still there.) The post starts with the following blockbuster:

This year October has 5 Saturdays, 5 Sundays, and 5 Mondays. This happens once every 823 years.

I can't imagine too many people who haven't noticed that the calendar shifts by one day every year (except in leap years, when dates on or after March 1 shift by two days, because of the addition of February 29). Mathematically, this one-day shift corresponds to the remainder of 1 that is left when you divide 365 by 7.

Without getting into calendar math or knowing anything other than the fact that the calendar shifts by that one day every year (and two in leap years), it's pretty clear that if October starts on a Saturday in 2011, it will start on:

Monday in 2012 (leap year, so Sunday is skipped)
Tuesday in 2013
Wednesday in 2014
Thursday in 2015
Saturday in 2016 (leap year, skipping Friday)

If we perform the same exercise going back in time, it's straightforward to determine that October started on:

Friday in 2010
Thursday in 2009
Wednesday in 2008
Monday in 2007
Sunday in 2006
Saturday in 2005

So, 5 years going forward, 6 years going back, and October starts on Saturday. So much for "every 823 years." The rest of the post is pure bunkum as well.

Cheers...