quality:corruption, stylistic:tone
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,

With respect to the Gregorian calendar:

In a Gregorian mean year, there are 365.2425 days, and thus exactly 52 + 71 ⁄ 400 or 52.1775 weeks (unlike the Julian year of 365.25 days or 52 + 5 ⁄ 28 ≈ 52.1786 weeks, which cannot be represented by a finite decimal expansion). There are exactly 20,871 weeks in 400 Gregorian years, so 3 September 1624 was a Tuesday just as was 3 September 2024.

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 Julian day number by seven (JD modulo 7 + 1) yields that date's ISO 8601 day of the week. For example, the Julian day number of 3 September 2024 is 2460557. Calculating 2460557 mod 7 + 1 yields 2, corresponding to Tuesday. In 1973, John Conway devised the Doomsday rule for mental calculation of the weekday of any date in any year.