There is a formula invented by the German clergyman Christian Zeller (1824–1899) for figuring out the day of the week of a given date. This would be a good exercise for students in algebra who are learning to use variables and to evaluate formulas. You will need to explain the greatest integer function to them (indicated by brackets [] in the formula below). At this level, just explain it as integer division (disregard the remainder).
Reverend Zeller's Day Date Formula converts the date mm/dd/yyyy to the day of the week. His formula only works for dates after September 15, 1752, the
year most English speaking countries adopted the Gregorian calendar.
First Zeller had to fix the months:
JAN = 11 of the previous year
FEB = 12 of the previous year
MAR = 1
APR = 2
MAY = 3
JUN = 4
JUL = 5
AUG = 6
SEP = 7
OCT = 8
NOV = 9
DEC = 10
You may think of this as starting the year with March. If the date that you are using is in January or February, you must use the PREVIOUS year in the formula.
Let M = new month from above
Let C = first two digits of the year
Let Y = last two digits of the year
Let D = day of the month
Compute the following sum:
Remember that [ ] means Greatest Integer Function.
If SUM < 0 Then add 7 to SUM.
Next, find the remainder of SUM / 7.
0 = SUNDAY
1 = MONDAY
2 = TUESDAY
3 = WEDNESDAY
4 = THURSDAY
5 = FRIDAY
6 = SATURDAY
EXAMPLES:
(1) Determine the day of the week on which Abraham Lincoln was shot (April 14, 1865).
M = 2 C = 18 Y = 65 D = 14
Dividing SUM by 7, the remainder = 5, which is FRIDAY
(2) Determine the day of the week on which the Columbine High School massacre occurred
(April 20, 1999).
M = 2 C = 19 Y = 99 D = 20
Dividing SUM by 7, the remainder = 2, which is TUESDAY
(3) Determine the day of the week on which February 28, 2014 fell.
M = 12 C = 20 Y = 13 (PREVIOUS YEAR) D = 28
Dividing SUM by 7, the remainder = 5, which is FRIDAY
(4) Determine the day of the week on which Mount Saint Helens erupted (May 18, 1980).
M = 3 C = 19 Y = 80 D = 18
Dividing SUM by 7, the remainder = 0, which is SUNDAY
"Monday's Child" is one of many fortune-telling songs, popular as nursery rhymes for children. It is supposed to tell a child's character or future based on the day he or she was born and to help young children remember the days of the week.
Monday's child is fair of face,
Tuesday's child is full of grace,
Wednesday's child is full of woe,
Thursday's child has far to go.
Friday's child is loving and giving,
Saturday's child works hard for a living,
But the child born on the Sabbath Day,
Is fair and wise and good in every way.