Talk:Perfect month: Difference between revisions

A perfect month or a rectangular month designates a month whose number of days is divisible by the number of days in a week and whose first day corresponds to the first day of the week.^[1][2] This causes the arrangement of the days of the month to resemble a rectangle. In the Gregorian calendar, this arrangement can only occur for the month of February.

To satisfy such an arrangement in the Gregorian calendar, the number of days in the month must be divisible by seven. Only the month of February of a common year can meet this constraint as the month has 28 days, a multiple of 7.^[3]
For a February to be a perfect month, the month must start on the first day of the week (usually considered to be Sunday or Monday). For Sunday-first calendars, this means that the year must start on a Thursday, and for Monday-first calendars, the year must start on a Friday. It must also occur in a common year, as the phenomenon does not occur when February has 29 days.

In the Gregorian calendar, the phenomenon occurs every six years or eleven years following a 6-11-11, 11-6-11, or an 11-11-6 sequence until the end of the 21st century. The most recent perfect months were February 2015 (Sunday-first) and February 2021 (Monday-first).^[4] Due to calculation rules, the years 1700, 1800, and 1900 are not leap years, causing a shift in the sequence with a spacing of twelve years. For example, in Sunday-first calendars, there are spacings between 1795 and 1807; however 2094, 2100 and 2106 will all feature perfect months with spacings of six years on Monday-first calendars.

The calendar arrangement brings together notions of harmony and organization.^[5][6]