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The solar cycle is a 28-year cycle of the
Julian calendar The Julian calendar, proposed by Julius Caesar Gaius Julius Caesar (; 12 July 100 BC – 15 March 44 BC) was a Roman Roman or Romans usually refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century B ...
, and 400-year cycle of the
Gregorian calendar The Gregorian calendar is the calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single, speci ...
with respect to the
week A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside—although not strictly part of—the Gregorian calendar. In many languages, the days of the we ...

week
. It occurs because
leap years ''Leap Years'' is a 2001 2001 was designated as International Year of Volunteers. Events January * January 1 January 1 or 1 January is the first day of the year in the Gregorian Calendar. There are 364 days remaining until the end o ...
occur every 4 years and there are 7 possible days to start a
leap year A leap year (also known as an intercalary year or wikt:bissextile, bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astron ...

leap year
, making a 28-year sequence. This cycle also occurs in the
Gregorian calendar The Gregorian calendar is the calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single, speci ...
, but it is interrupted by years such as 1800, 1900, 2100, 2200, 2300 and 2500, which are divisible by four but which are common years. This interruption has the effect of skipping 16 years of the solar cycle between February 28 and March 1. Because the Gregorian cycle of 400 years has exactly 146,097 days, i.e. exactly 20,871 weeks, one can say that the Gregorian so-called solar cycle lasts 400 years. Calendar years are usually marked by
Dominical letterDominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter (or pair of letters for leap years) depending on which day of the week the year starts ...
s indicating the first
Sunday Sunday is the day of the week between Saturday and Monday. In most Western countries, Sunday is a day of rest and a part of the Workweek and weekend, weekend, whereas in much of the rest of the world, it is considered the first day of the week. ...

Sunday
in a new year, thus the term solar cycle can also refer to a repeating sequence of Dominical letters. Unless a year is not a leap year due to Gregorian exceptions, a sequence of calendars is reused every 28 years.


See also

*
Birkat Hachama ''Birkat Hachama'' (ברכת החמה, "Blessing of the Sun") refers to a rare Judaism, Jewish berakhah, blessing that is recited to the Creator, thanking Him for creating the sun. The blessing is recited when the sun completes its cycle every 28 ...
*
Dominical letterDominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter (or pair of letters for leap years) depending on which day of the week the year starts ...
*
Doomsday rule The Doomsday rule is an algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loop ...

Doomsday rule
*
Friday the 13th Friday the 13th is considered an unlucky day in Western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmani ...


References


Further reading

* C. R. Cheney (rev. Michael Jones), 2012: ''Handbook of dates'' (2nd edition), CUP


External links


The ISO 8601 calendar using week numbers
explained using
Dominical letterDominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter (or pair of letters for leap years) depending on which day of the week the year starts ...
s. Calendars category:Gregorian calendar Julian calendar Units of time {{time-stub