Doomsday of a year

E637559

calendar concept computational calendar method day-of-week rule

Doomsday of a year is a specific weekday that recurs on certain anchor dates throughout that year, enabling quick mental calculation of any date’s weekday.

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All labels observed (2)

Label	Occurrences
Doomsday (reference weekday for a year)	1
Doomsday of a year canonical	1

Statements (49)

Predicate	Object
instanceOf	calendar concept ⓘ computational calendar method ⓘ day-of-week rule ⓘ
appliesTo	Gregorian calendar NERFINISHED ⓘ Julian calendar NERFINISHED ⓘ
basedOn	modular arithmetic ⓘ weekday cycles ⓘ
calculatedFrom	century anchor day ⓘ leap year status ⓘ year's last two digits ⓘ
developedBy	John Horton Conway NERFINISHED ⓘ
hasAdvantage	does not require written tables ⓘ enables fast mental weekday computation ⓘ requires only simple arithmetic ⓘ
hasAnchorDate	April 4 ⓘ August 8 ⓘ December 12 ⓘ February 28 in common years ⓘ February 29 in leap years ⓘ July 11 ⓘ June 6 ⓘ May 9 ⓘ November 7 ⓘ October 10 ⓘ September 5 ⓘ the last day of February ⓘ
hasDefinition	a specific weekday on which a set of anchor dates fall in a given year ⓘ
hasLimitation	assumes use of a specific calendar system ⓘ differs between Gregorian and Julian calendars ⓘ
hasOutcome	a weekday index from 0 to 6 ⓘ
hasProperty	can be any of the seven weekdays ⓘ depends on the year number ⓘ is constant within a given year ⓘ is the same weekday for all doomsday dates in that year ⓘ repeats every 400 years in the Gregorian calendar ⓘ
hasStep	adjust for the year's last two digits ⓘ find the century anchor day ⓘ reduce result modulo 7 ⓘ
isComponentOf	calendar arithmetic ⓘ
isTaughtIn	mental calculation courses ⓘ recreational mathematics ⓘ
partOf	Doomsday algorithm NERFINISHED ⓘ
relatedTo	Doomsday rule NERFINISHED ⓘ Zeller's congruence NERFINISHED ⓘ anchor day of a century ⓘ mental calculation techniques ⓘ perpetual calendar ⓘ
usedFor	determining the weekday of any date in the same year ⓘ mental calculation of weekdays ⓘ

Referenced by (2)

Full triples — surface form annotated when it differs from this entity's canonical label.

Conway’s Doomsday algorithm → usesConcept → Doomsday of a year ⓘ

Conway’s Doomsday algorithm → namedAfter → Doomsday of a year ⓘ

this entity surface form: Doomsday (reference weekday for a year)