Day Finding

Date: 07/17/97 at 12:58:15
From: Roshan Anthonypillai
Subject: Day finding

What is the formula to find the day of the week, given the date, 
month, and year?

Thanks.

Roshan

Date: 08/16/97 at 15:20:53
From: Doctor Terrel
Subject: Re: Day finding

Hi Roshan,

I found something that might help you - from Australia!  Isn't that 
neat?  Here it is...


Calculating the Day of the Week For Any Year

Here is a standard method suitable for mentally computing the day of 
the week from the date:

   1. Take the last two digits of the year.
   2. Divide by 4, discarding any fraction (remainder).
   3. Add the day of the month.
   4. Add the month's key value: JFM AMJ JAS OND 144 025 036 146

[You should take that last line to mean:  jan = 1, feb = 4, mar = 4, 
etc.]

   5. Subtract 1 for January or February of a leap year.
   6. For a Gregorian date, add 0 for 1900's, 6 for 2000's, 4 for 
      1700's, 2 for 1800's;

for other years, add or subtract multiples of 400.

   7. For a Julian date, add 1 for 1700's, and 1 for every additional 
      century you go back.
   8. Add the last two digits of the year.
   9. Divide by 7 and take the remainder.

 Now 1 is Sunday, the first day of the week, 2 is Monday, and so on.


Calculating the Day of the Week for the Current Year

A good mnemonic rule to help on the computation of the day of the week 
is as follows.

In any given year the following days come on the same day of the week:
(Note to U.S. citizens - in Australia we use day/month instead of 
month/day, so 4/7 is July 4.)

 4/4
 6/6
 8/8
 10/10
 12/12

To remember the next four, remember that I work from 9-5 at a 7-11 so

 9/5
 5/9
 7/11
 11/7
 and the last day of Feb.

In 1996, these dates all fall on a Thursday. To find the day that the 
4th of July falls on, for example, use the fact that 11/7 is a 
Thursday, and hence the 4/7 is also.

Taken from:

http://www.lib.ox.ac.uk/internet/news/faq/archive/sci-math-faq.dayweek.html   

-Doctor Terrel,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/