THE ORIGIN OF DAY NAMES

The days of the week were named by ancient Romans with the Latin words for the Sun, the Moon, and the five known planets. These names have survived in European languages, but English names also reflect Anglo-Saxon and Norse influences.

ENGLISH	LATIN	FRENCH	ITALIAN	SPANISH	ANGLO-SAXON AND NORSE
SUNDAY	dies Solis (Sol’s day)	dimanche domenica domingofrom the Latin for “Lord’s day”			Sunnandaeg (Sun’s day)
MONDAY	dies Lunae (Luna’s day)	lundi	lunedì	lunes	Monandaeg (Moon’s day)
TUESDAY	dies Martis (Mars’s day)	mardi	martedì	martes	Tiwesdaeg (Tiw’s day)
WEDNESDAY	dies Mercurii (Mercury’s day)	mercredi	mercoledì	miércoles	Wodnesdaeg (Woden’s day)
THURSDAY	dies Jovis (Jupiter’s day)	jeudi	giovedì	jueves	Thursdaeg (Thor’s day)
FRIDAY	dies Veneris (Venus’s day)	vendredi	venerdì	viernes	Frigedaeg (Frigga’s day)
SATURDAY	dies Saturni (Saturn’s day)	samedi	sabato	sábado	Saeterndaeg (Saturn’s day)
		from the Latin for “Sabbath”

How to Find the Day of the Week for Any Given Date

To compute the day of the week for any given date as far back as the mid–18th century, proceed as follows:

Add the last two digits of the year to one-quarter of the last two digits (discard any remainder), the day of the month, and the month key from the key box below. Divide the sum by 7; the remainder is the day of the week (1 is Sunday, 2 is Monday, and so on). If there is no remainder, the day is Saturday. If you're searching for a weekday prior to 1900, add 2 to the sum before dividing; prior to 1800, add 4. The formula doesn't work for days prior to 1753. From 2000 through 2099, subtract 1 from the sum before dividing. 

Example:

THE DAYTON FLOOD WAS ON MARCH 25, 1913.

Last two digits of year: 13

One-quarter of these two digits: 3

Given day of month: 25

Key number for March: 4

Sum: 45

45 ÷ 7 = 6, with a remainder of 3. The flood took place on Tuesday, the third day of the week.

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