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. This causes the arrangement of the days of the month to resemble a rectangle. In the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...
, this arrangement can only occur for the month of February.
Constraints
To satisfy such an arrangement in the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...
, the number of days in the month must be divisible by seven. Only the month of February of a
common year
A common year is a calendar year with 365 days, as distinguished from a ''leap year'', which has 366 days. More generally, a common year is one without Intercalation (timekeeping), intercalation. The Gregorian calendar, used by the majority of ...
can meet this constraint as the month has 28 days, a
multiple of 7.
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
Thursday is the day of the week between Wednesday and Friday. According to the ISO 8601 international standard, it is the fourth day of the week. In countries which adopt the "Sunday-first" convention, it is the fifth day of the week.
Name
Th ...
, and for Monday-first calendars, the year must start on a
Friday
Friday is the day of the week between Thursday and Saturday. In countries that adopt the traditional "Sunday-first" convention, it is the sixth day of the week. In countries adopting the ISO 8601-defined "Monday-first" convention, it is the fifth ...
. It must also occur in a
common year
A common year is a calendar year with 365 days, as distinguished from a ''leap year'', which has 366 days. More generally, a common year is one without Intercalation (timekeeping), intercalation. The Gregorian calendar, used by the majority of ...
, as the phenomenon does not occur when February has 29 days.
Occurrence
In the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...
, 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). Due to
calculation rules, the years 1700, 1800, and 1900 are not leap years, causing a shift in the sequence with two instances of three consecutive spacings of six years each (1693, 1699, 1705, 1711 and 1789, 1795, 1801, 1807) and a spacing of twelve years between 1891 and 1903 for Sunday-first calendars; or two consecutive spacings of six years each (1694, 1700, and 1706) and spacings of twelve years between 1790 and 1802, and 1897 and 1909 respectively for Monday-first calendars. The Gregorian calendar repeats every 400 years, so 2094, 2100, and 2106 will all feature perfect months with spacings of six years on Monday-first calendars; while 2093, 2099, 2105, and 2111 will all feature perfect months with spacings of six years on Sunday-first calendars.
The next perfect months will be February 2026 (Sunday-first) and February 2027 (Monday-first).
Attributes
The calendar arrangement brings together notions of harmony and organization.
See also
*
Palindrome#Dates
*
Perfectionism (psychology)
Perfectionism, in psychology, is a broad personality trait characterized by a person's concern with striving for flawlessness and perfection and is accompanied by critical self-evaluations and concerns regarding others' evaluations. It is best ...
*
Perfectionism (philosophy)
In ethics and value theory, perfectionism is the persistence of will in obtaining the optimal quality of spiritual, mental, physical, and material being. Thomas Hurka describes perfectionism as follows:
This moral theory starts from an account ...
References
{{Reflist
Calendars
February
Months