conclusion of the Sabbath, following the Hebrew Bible in which God created the world in six days and rested on the seventh. Christians set their Sabbath to Sunday, so as not to coincide with Judaism. Muslims set their Sabbath to Friday so as not to coincide with either Judaism or Christianity. Name The English word week comes from the Old English , ultimately from a Common Germanic , from a root "turn, move, change". The Germanic word probably had a wider meaning prior to the adoption of the Roman calendar, perhaps "succession series", as suggested by Gothic translating "order" in Luke 1:8. The seven-day week is named in many languages by a word derived from "seven". The archaism sennight ("seven-night") preserves the old Germanic practice of reckoning time by nights, as in the more common fortnight ("fourteen-night"). Hebdomad and hebdomadal week both derive from the Greek (, "a seven"). Septimana is cognate with the Romance terms derived from Latin ("seven mornings"). Slavic has a formation *tъ(žь)dьnь (Serbian , Croatian , Ukrainian , Czech , Polish ), from *tъ "this" + *dьnь "day". Chinese has , as it were "planetary time unit". Definition and duration A week is defined as an interval of exactly seven days, so that, except when passing through daylight saving time transitions or leap seconds, 1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds. With respect to the Gregorian calendar: 1 Gregorian calendar year = 52 weeks + 1 day (2 days in a leap year) 1 week = ≈ 22.9984% of an average Gregorian month In a Gregorian mean year, there are 365.2425 days, and thus exactly or 52.1775 weeks (unlike the Julian year of 365.25 days or ≈ 52.1786 weeks, which cannot be represented by a finite decimal expansion). There are exactly 20,871 weeks in 400 Gregorian years, so was a just as was . Relative to the path of the Moon, a week is 23.659% of an average lunation or 94.637% of an average quarter lunation. Historically, the system of dominical letters (letters A to G identifying the weekday of the first day of a given year) has been used to facilitate calculation of the day of week. The day of the week can be easily calculated given a date's Julian day number (JD, i.e. the integer value at noon UT): Adding one to the remainder after dividing the