Calendar math

science_man_88 · 2011-06-25, 00:28

I am almost positive there's another thread for this but one of my Facebook friends posted this lately:

Quote:

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 philosophy of Feng Shui. Those who read and do not copy will be without money. So let's all try our luck at this and see what happens . .

I explained some of the math that makes this impossible but would anyone else like to talk about this type of stuff ?

science_man_88 · 2011-06-25, 00:33

Quote:

Originally Posted by science_man_88

I am almost positive there's another thread for this but one of my Facebook friends posted this lately:

I explained some of the math that makes this impossible but would anyone else like to talk about this type of stuff ?

the math I used was:
1)7 days of the week to start a year on
2) either leap year or not
3) so 14 calendars possible.

I've been doing some math and to be 0 mod 7 even with an leap year turned not for the 400 year rule etc. this only takes at most 15 years.

Somebody correct me if I'm wrong.

ATH · 2011-06-25, 01:26

This happens every time the 1st of a month with 31 days (January, March, May, July, August, October, December) is a friday, or does it have to be July to fulfill this "myth"?

If not, it happens again in March 2013 and then August 2014. If it has to be July it happens again in July 2016, 2022, 2033 and so on.

A date is the same day of the week every .....5,6,11,6, 5,6,11,6, 5,6,11,6 .... years. Except when we pass a century not divisible by 400 like 2100. So it happens at most every 11 years if it has to be July, and alot more often if it can be any of the months with 31 days.

Christenson · 2011-06-25, 04:31

Quote:

Originally Posted by science_man_88

I am almost positive there's another thread for this but one of my Facebook friends posted this lately:

Quote:
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 philosophy of Feng Shui. Those who read and do not copy will be without money. So let's all try our luck at this and see what happens . .

I explained some of the math that makes this impossible but would anyone else like to talk about this type of stuff ?

SM88, there's half a dozen things here that should warn you about the garbage being posted by your facebook friend. First, it asks you to pass on the message to a bunch of your friends. Second, this is in return for a vague reward that is supposed to magically materialze. Third, their is a magical punishment if you don't. Fourth, the triggering event is supposed to be rare, but it triggers even your garbage detectors. Fifth a little mystical chinese philosophy is tossed in to help. You'd think they'd have noticed that traditional china reckons the years by the year of the dragon, the ox, etc. And something that happens every 823 years usually needs a little astronomy or astrology to help it...planets align or something.

I'd be surprised if you can't find this on snopes.com, which is sort of central clearinghouse for this kind of thing.

Your math sense in this case is fine....there are only 14 possible arrangements of the weekdays on the calendar (one for each of 7 days starting the year times 2 for leap-years), and they do repeat in cycles. (We'll ignore the fact that 1900 wasn't a leap year).

You might want to write your friend and tell him that Facebook might not take kindly to his little "chain letter" -- he should check his terms of service.

Brian-E · 2011-06-25, 10:17

Apparently there was more nonense of this kind distributed with the chain letter too, as exposed in Rev. Anaglyph's tetherd cow blog. He typifies some of the silly observations involving dates in 2011 as "cherry picking", highlighting this technique as an important method of promoting beliefs which have no genuine scientific basis.

Christenson · 2011-06-25, 12:59

Aha!!! Is this the real "SMALL LAW of strong numbers" ? (As opposed to its correct, spooneristic analog, the strong law of small numbers.....)

Brian-E · 2011-06-25, 13:34

Quote:

Originally Posted by Christenson

Aha!!! Is this the real "SMALL LAW of strong numbers" ? (As opposed to its correct, spooneristic analog, the strong law of small numbers.....)

Maybe. But the spooneristic analog actually states that all numbers beyond a certain length are characterised by a diminutive straw.

cheesehead · 2011-06-25, 21:15

I posted an explanation like ATH's to my junior-high-school-class group mailing list, then added, "What would _really_ be unusual would be a July with five Fridays, five Mondays and five Wednesdays."

ATH · 2011-06-26, 00:00

If you want something more rare, try choosing some dates in a leap year that crosses February 29th.

For example 2012 January 1st, April 1st and July 1st all fall on a sunday: http://www.timeanddate.com/calendar/...2012&country=2
This doesn't happen again for 28 years (5+6+11+6) in 2040: http://www.timeanddate.com/calendar/...2040&country=2
but still thats far from the 823 years claimed in the "myth".

For something more rare we can choose an event on the 28 year cycle but involving a century not divided by 400 like year 2100. So we choose the year 2072 in which 1st of January, April, July all fall on a friday: http://www.timeanddate.com/calendar/...2072&country=2
This should happen again in 2100 but since 2100 is not a leap year like the normal 4 year cycle, it doesn't happen again until 2112: http://www.timeanddate.com/calendar/...2112&country=2

science_man_88 · 2011-06-26, 00:01

Quote:

Originally Posted by ATH

If you want something more rare, try choosing some dates in a leap year that crosses February 29th.

For example 2012 January 1st, April 1st and July 1st all falls on a sunday: http://www.timeanddate.com/calendar/...2012&country=2
This doesn't happen again for 28 years (5+6+11+6) in 2040: http://www.timeanddate.com/calendar/...2040&country=2
but still thats far from the 823 years claimed in the "myth".

is there anything the myth could be based on that does last 823 seems to remind me of something lunar if I remember correct.

Christenson · 2011-06-26, 02:42

The myth is clearly just made-up, scientific-sounding mumbo-jumbo.

Now, we want something rare....so we need something on a different cycle than 365 days...the lunar month is a good candidate. Why don't you calculate how often the full moon falls on the first of the month, and it's a Friday? Or there is a total eclipse of the sun, somewhere on earth at the same time?

But, as we are supposedly coming from China, how about something based on it being the year of the dragon, too?

2011-06-25, 01:26	#3
ATH Einyen Dec 2003 Denmark 2²·863 Posts	This happens every time the 1st of a month with 31 days (January, March, May, July, August, October, December) is a friday, or does it have to be July to fulfill this "myth"? If not, it happens again in March 2013 and then August 2014. If it has to be July it happens again in July 2016, 2022, 2033 and so on. A date is the same day of the week every .....5,6,11,6, 5,6,11,6, 5,6,11,6 .... years. Except when we pass a century not divisible by 400 like 2100. So it happens at most every 11 years if it has to be July, and alot more often if it can be any of the months with 31 days. Last fiddled with by ATH on 2011-06-25 at 01:28

2011-06-26, 00:00	#9
ATH Einyen Dec 2003 Denmark 2²×863 Posts	If you want something more rare, try choosing some dates in a leap year that crosses February 29th. For example 2012 January 1st, April 1st and July 1st all fall on a sunday: http://www.timeanddate.com/calendar/...2012&country=2 This doesn't happen again for 28 years (5+6+11+6) in 2040: http://www.timeanddate.com/calendar/...2040&country=2 but still thats far from the 823 years claimed in the "myth". For something more rare we can choose an event on the 28 year cycle but involving a century not divided by 400 like year 2100. So we choose the year 2072 in which 1st of January, April, July all fall on a friday: http://www.timeanddate.com/calendar/...2072&country=2 This should happen again in 2100 but since 2100 is not a leap year like the normal 4 year cycle, it doesn't happen again until 2112: http://www.timeanddate.com/calendar/...2112&country=2 Last fiddled with by ATH on 2011-06-26 at 00:06

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2011-06-25, 10:17	#5
Brian-E "Brian" Jul 2007 The Netherlands 110011001110₂ Posts	Apparently there was more nonense of this kind distributed with the chain letter too, as exposed in Rev. Anaglyph's tetherd cow blog. He typifies some of the silly observations involving dates in 2011 as "cherry picking", highlighting this technique as an important method of promoting beliefs which have no genuine scientific basis.

2011-06-25, 12:59	#6
Christenson Dec 2010 Monticello 5·359 Posts	Aha!!! Is this the real "SMALL LAW of strong numbers" ? (As opposed to its correct, spooneristic analog, the strong law of small numbers.....)

2011-06-25, 21:15	#8
cheesehead "Richard B. Woods" Aug 2002 Wisconsin USA 17014₈ Posts	I posted an explanation like ATH's to my junior-high-school-class group mailing list, then added, "What would _really_ be unusual would be a July with five Fridays, five Mondays and five Wednesdays."

2011-06-26, 02:42	#11
Christenson Dec 2010 Monticello 5·359 Posts	The myth is clearly just made-up, scientific-sounding mumbo-jumbo. Now, we want something rare....so we need something on a different cycle than 365 days...the lunar month is a good candidate. Why don't you calculate how often the full moon falls on the first of the month, and it's a Friday? Or there is a total eclipse of the sun, somewhere on earth at the same time? But, as we are supposedly coming from China, how about something based on it being the year of the dragon, too?