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Calendar year
 
 
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According to the Gregorian calendar
Gregorian calendar

The Gregorian calendar is the internationally accepted civil calendar. It was first proposed by the Calabrian doctor Aloysius Lilius, and decreed by Pope Gregory XIII, after whom it was named, on 24 February 1582 by the papal bull Inter gravissimas....
, the calendar year begins on January 1 and ends on December 31.

Generally speaking, a calendar year begins on the New Year's day
New Year

The New Year is an event that happens when a culture celebrates the end of one year and the beginning of the next year. Cultures that measure yearly calendars all have New Year celebrations....
 of the given calendar system and ends on the day before the following New Year's day. In the Gregorian calendar, this is normally 365 days, but 366 days in a leap year
Leap year

A leap year is a year containing one or more extra days in order to keep the calendar year synchronized with the astronomical year or seasonal year....
, giving an average length of 365.2425 days.

By convention, a calendar year consists of a natural number
Natural number

In mathematics, a natural number can mean either an element of the Set = *n = = ? = ? ...
 of day
Day

A day is a units of measurement of time equivalent to approximately 24 hours. It is not an International System of Units unit but it is accepted for use with SI....
s.






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According to the Gregorian calendar
Gregorian calendar

The Gregorian calendar is the internationally accepted civil calendar. It was first proposed by the Calabrian doctor Aloysius Lilius, and decreed by Pope Gregory XIII, after whom it was named, on 24 February 1582 by the papal bull Inter gravissimas....
, the calendar year begins on January 1 and ends on December 31.

Generally speaking, a calendar year begins on the New Year's day
New Year

The New Year is an event that happens when a culture celebrates the end of one year and the beginning of the next year. Cultures that measure yearly calendars all have New Year celebrations....
 of the given calendar system and ends on the day before the following New Year's day. In the Gregorian calendar, this is normally 365 days, but 366 days in a leap year
Leap year

A leap year is a year containing one or more extra days in order to keep the calendar year synchronized with the astronomical year or seasonal year....
, giving an average length of 365.2425 days.

By convention, a calendar year consists of a natural number
Natural number

In mathematics, a natural number can mean either an element of the Set = *n = = ? = ? ...
 of day
Day

A day is a units of measurement of time equivalent to approximately 24 hours. It is not an International System of Units unit but it is accepted for use with SI....
s. To reconcile the calendar year with an astronomical cycle (which could not possibly be reckoned in a whole number of days), certain years contain extra days
Intercalation

Intercalation is the insertion of a leap day, week or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months....
. Through further insertion of non-day units of time, the calendar year can be further synchronized; however, these extra units of time are not considered part of the calendar.

Length

In the Gregorian calendar, the length of a calendar year is normally 365 days, but 366
366

Events...
 days in a leap year
Leap year

A leap year is a year containing one or more extra days in order to keep the calendar year synchronized with the astronomical year or seasonal year....
 giving an average length of 365.2425 days. This is very close to the average length of the Islamic calendar
Islamic calendar

The Islamic calendar or Muslim calendar or Hijri calendar is a lunar calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals....
 (based on the average time between successive vernal equinoxes, currently 365.2424 days and increasing marginally). Other formula-based calendars can have lengths which are further out of step with the solar cycle, for example, the Julian calendar
Julian calendar

The Julian calendar, a reform of the Roman calendar, was introduced by Julius Caesar in 46 BC, and came into force in 45 BC . It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year, known at least since Hipparchus....
 had an average length of 365.25 days, and the Hebrew calendar
Hebrew calendar

The Hebrew calendar or Jewish calendar is a lunisolar calendar used by Jews, now predominantly for religious purposes. It is used to reckon the Jewish New Year and dates for Jewish holidays, and also to determine appropriate Torah reading of Torah portions, Yahrzeits , and daily Psalm reading, among many ceremonial uses....
 has an average length of 365.2468 days.
The astronomer's mean tropical year which is averaged over equinoxes and solstices is currently 365.24219 days, slightly shorter than the average length of the year in most calendars, but astronomer's value changes over time, so William Herschel
William Herschel

Sir Frederick William Herschel, Fellow of the Royal Society Royal Guelphic Order was a German-born British astronomer and composer who became famous for discovering Uranus....
's suggested correction to the Gregorian calendar may become unnecessary by the year 4000.

Subdivisions


Quarters
The calendar year can be divided into 4 quarters, often abbreviated Q1, Q2, Q3 and Q4.
  • First quarter: from the beginning of January to the end of March
  • Second quarter: from the beginning of April to the end of June
  • Third quarter: from the beginning of July to the end of September
  • Fourth quarter: from the beginning of October to the end of December


See also

  • Calendar
    Calendar

    A calendar is a system of organize days for a social, religious, commercial or administrative purpose. This organization is done by giving names to periods of time ? typically days, weeks, months and years....
  • Calendar reform
    Calendar reform

    A calendar reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar....
  • Fiscal year
  • ISO 8601
    ISO 8601

    ISO 8601 is an international standard for calendar date and time representations issued by the International Organization for Standardization . Specifically, the standard is titled "Data elements and interchange formats ? Information interchange ? Representation of dates and times"....
  • ISO week date
    ISO week date

    The International_Organization_for_Standardization week date system is a leap week calendar system that is part of the ISO 8601 date and time standard....
  • Leap year
    Leap year

    A leap year is a year containing one or more extra days in order to keep the calendar year synchronized with the astronomical year or seasonal year....
  • Seasonal year
    Seasonal year

    The seasonal year is the time between successive recurrences of a seasonal event such as the flooding of a river, the migration of a species of bird, or the flowering of a species of plant....
  • Year
    Year

    A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, a "Martian year" is the time in which Mars completes its own orbit....