Names of the days of the week is followed by a number indicating the day: "Monday" is literally "star day one", "Tuesday" is "star day two", etc. The exception is Sunday, where rì (日), meaning "sun" or "day", is used instead of a number. In Swahili, the day begins at sunrise, unlike in the Arabic and Hebrew calendars where the day starts at sunset (therefore an offset of twelve hours), and unlike in the Western world where the day starts at midnight (therefore an offset of six hours). Saturday is therefore the first day of the week, as it is the day that includes the first night
Determination of the day of the week the intended design objective. The tabular forerunner to Tøndering's algorithm is embodied in the following K&R C function. With minor changes, it was adapted for other high level programming languages such as APL2. Posted by Tomohiko Sakamoto on the comp.lang.c Usenet newsgroup in 1992, it is accurate for any Gregorian date. IBM's Rata Die method requires that one knows the "key day" of the proleptic Gregorian calendar i.e. the day of the week of January 1, AD 1 (its first date). This has to be done to establish the remainder number based on which the day of the week is