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The Latest Facebook Chain Letter Meme

Recently, two friends posted this to their Facebook status updates:

I was just told and I'm not superstitious, but this year July has 5 Fridays, 5 Saturdays and 5 Sundays. This happens once every 823 years. This is called money bags. So, copy this to your status and money will arrive within 4 days. Based on Chinese Feng Shui. The one who does not copy will be without money. I cannot let that person be.............. ME! Good Luck
This is incorrect.  I'm going to ignore the superstitious aspects (and the Feng Shui, which is used here in a way I'm unfamiliar with) for a moment, and focus on what I can prove.

Whoever originally wrote this apparently has no idea how the Gregorian calendar works: The calendars recycle every 400 years.  That means that the calendar for 2000 would have been the same as the calendar for the year 1600 (Although the RC Church adopted the Gregorian calendar in 1582, the British Empire, and thus the American colonies, did not adopt it until 1752).  In turn, this means that the calendar for 2011 is exactly the same as the calendar for 1611 and will be the same for the calendar for 2411.  Therefore, at the very minimum, 823 years is wrong and should be 400 years.

But even that would have been wrong.

A July that has 5 Fridays, Saturdays and Sundays must have started on a Friday (that would make the 29th a Friday, the 30th a Saturday, and the 31st a Sunday, which would be the 5th Friday, Saturday, and Sunday of that month).  Since 1900, this has happened 15 times: 1904, 1910, 1921, 1927, 1932, 1938, 1949, 1955, 1960, 1966, 1977, 1983, 1988, 1994, and 2005.  This means that *on average* in the last 111 years, it has happened every 7.133 years.

Comments

( 2 comments — Leave a comment )
tomd1969
Jan. 11th, 2011 06:09 pm (UTC)
A clarification
While the calendar does repeat every 28 years, too (1986 has the same exact calendar as 2011), that is only true "locally." For example, 1872 was *not* the same as 1900; while they both started on Monday, 1872 was a leap year and 1900 was not. It is more correct to say that the Gregorian calendar recycles every 400 years (for example, 1611 started on a Saturday, as did 2011).
tomd1969
Jan. 11th, 2011 07:19 pm (UTC)
Re: A clarification
Of course, I made an error here. Darn it all to heck. *1983* has the same exact calendar as 2011. I'm still getting the hang of all this new-fangled maff.
( 2 comments — Leave a comment )