- In the astronomical sense, various definitions of the term “year” are based on the duration of the earth's orbit around the sun or the apparent movement of the sun in the sky. A distinction is made between the sidereal year , the tropical year and the anomalistic year , all of which last around 365¼ days with slight mutual deviations. Occasionally “year” is also related to the period of orbit of other celestial bodies around their central star, one then speaks of “Mars year”.
- The civil year or calendar year is based on the tropical year. It takes either 365 days ( common year ) or 366 days ( leap year ). In everyday life, the term “year” means the respective time from January 1st to December 31st.
- Annual classifications that differ from the calendar calculation are culturally (e.g. school year , memorial year ) or individual (e.g. year of life ).
- Phenological years encompass the cycle of the four seasons . They are mostly based on certain natural events in the course of the year.
From the point of view of physical metrology , a “year” (without specifying the assessment basis) does not represent a unit of measurement ; in the international system of units , a unit symbol a (for the Latin annus “year”) is tolerated in certain contexts. There is no binding standard for the length of a year, but the above values appear as more specific normative bases.
In the calendar calculation, calendar year or civil year is generally the name for the average year length of the calendar system , regardless of how common and leap years are calculated. The year (in the concept of the first 1 to 31 12) is a calendar year of a solar calendar in distinction to the Lunar year ( lunar year ) and the Lunisolarjahr that distinctly different lengths have. The expression “civil calculation of time” refers to the distinction between “physical”, “technical” or “astronomical”.
The DIN 1355-1 standard makes a statement about the times of the beginning and the end of the civil year, but not about the time span between them, e.g. For example: "The calendar year begins on January 1st" [00:00] "and ends on the following December 31st" [24:00]
This results in the length of a civil year:
- 1 calendar year = 365 or 366 calendar days
- 1 common year = 31,536,000 seconds; 1 (calendar) leap year = 31,622,400 seconds
Occasionally the calendar year length is also changed by inserting coordinated leap seconds . The leap seconds are inserted on June 30th or December 31st, and if necessary also on March 31st or September 30th, whereby these calendar days can be one second longer.
The leap days adjust the average calendar year to the tropical year . The leap seconds, on the other hand, serve to adapt the average calendar day to the mean sunny day, so they coordinate the coordinated universal time UTC (coordinated universal time) with the universal time UT (universal time) and the atomic time TAI.
The year is divided into 12 months . These fluctuate in length in the civil calendar.
- 1 calendar year = 12 calendar months
A civil year lasts 52 weeks (7 days) and one or two days. A calendar week lasts from Monday to Sunday and is counted regardless of the year, so that 52 or 53 calendar weeks can fall in a year. The first calendar week of the year is the week “in which at least four of the first 7 days of January fall”, i. In other words, January 4th is always in the first calendar week.
- 1 calendar year = 52 weeks + 1 or 2 calendar days
|2020 in other calendars
|From urbe condita
|- 60 year cycle
- CCXXVIII CCXXIX
|- Vikram Sambat
|- Shaka Samvat
|- Nengō (era):
|- Dangun era
|- Juche era
|Thai solar calendar
According to ISO 8601, the calendar years are numbered consecutively with the year starting from zero . A single calendar year is thus clearly described and becomes the basic quantity of the calendar and part of the calendar date . Depending on the date format , it is listed with two or four digits .
- The current year is 2020 .
- Annual Calendar - The index of all years, decades, centuries, and millennia.
Beginning of the year
Economic and statistical definitions
- Fiscal year
- The period for a balance , too: fiscal year , fiscal year , financial year . A fiscal year does not necessarily have to start with a calendar year.
The duration of a financial year corresponds to that of the civil year .
- Bank year
- In the interest calculation, in addition to the calendar , usages for exactly 360 calendar days are common.
There are also numerous other financial years :
- The brewing year lasts from October 1st to September 30th of the following year.
- The hunting year begins on April 1st and ends on March 31st of the following calendar year. The hunting year is used to compile route statistics and the length of hunting leases is usually specified in the hunting lease contracts for the hunting years.
In different calendars
Other calendar systems use different definitions of the length and the beginning of a year as well as different reference dates , i.e. different year numbers. For example, mid-2006 is the year 1427 according to the Islamic calendar, 5766 in the Jewish calendar , and 丙戌 “fire dog” in the traditional Chinese calendar .
- Gregorian calendar year
For historical reasons, the calendar currently used worldwide and - especially in Europe - legally valid calendar is the Gregorian calendar . The Gregorian calendar year is a solar calendar and is based on the tropical year (solar year). In everyday life, the "Gregorian year" means the time from New Year to New Year's Eve .
The long-term mean length of the calendar year according to the Gregorian calendar (without taking into account coordinated universal time ):
- 365.2425 days = 365 days, 5 hours, 49 minutes, 12 seconds = 31,556,952 seconds.
The length is calculated from the fact that, according to the switching rules of the Gregorian calendar, 97 leap days are inserted within 400 years. As with all solar calendars, these rules try to approximate the civil year of the earth's true period of rotation around the sun - the tropical year - as simply as possible and yet with sufficient accuracy ( see → #In astronomy ).
- Church year
- The Roman Catholic and Protestant church years begin on the 1st Sunday in Advent .
The Orthodox church year is structured similarly, but begins on September 1st.
See also: Jubilee year , Sabbath year - a particularly holy year every 50 years
- Lunisolar year
- A solar year with lunar months . The length varies between 353 and 385 days, depending on the leap months and month lengths.
- Jewish year
- The Jewish year is a lunisolar year. To align with the solar year, its normal year has 12 lunar months (proper 354 days) and its leap year has 13 lunar months (proper 384 days). The civil Jewish year begins in autumn with the month of Tishri. In this, according to Jewish tradition , Adam and Eve were created. In biblical times it began in spring with the month of Nisan, the month of redemption, in which the Israelites set out from Egypt. The religious Jewish year begins with the month of Nisan, with Tishri being the seventh month of the year.
For further special calendar years see the list of calendar systems .
As a kinky year is defined as the longest calendar year history that occurred (46 BC..) With the introduction of the Julian calendar, it was 445 days long; see also year zero . The shortest year was 1582 when the introduction of the Gregorian calendar skipped 10 days.
The longest year in the civil calendar so far was 1972, when the leap year was one day longer than usual and also two coordinated leap seconds . Since then, more than a leap second in a single year has never been necessary and will not be foreseen in the foreseeable future.
In the geosciences
Calling the time between two natural events a year corresponds to the most original and intuitive concept of the course of the year as a cycle of the seasons . This can be the period between two spring floods of a river, certain bird migrations , agricultural events or the first frost . Definitions in this sense are:
- Meteorological year
- The year of meteorology begins with the meteorological winter of the northern hemisphere on December 1st of the previous calendar year. The meteorological seasons always include full calendar months to make statistics easier.
- Hydrological year, discharge year
- November 1 to October 31 (DIN 4049) or October 1 to September 30 (Austria, Switzerland)
- Phenological year
- The phenology examines the actual occurrence of certain botanical events in a region. For Europe it begins with the arrival of early spring when hazel and snowdrops begin to bloom. It has ten seasons (in Central Europe).
The zero point of the calendar is irrelevant for geological dating, here years are generally stated in 'millions of years before today': million years ago (mya) , besides bya is also possible for billion years ago , 'billions of years before today'. Periods of time are then given in Ma (mega years), in English-speaking countries also with yr instead of a .
Without further additions, "year" means the solar year :
"Orbit" is a question of reference points, which are constantly shifting due to the complex force and movement relationships in the solar system, so there are some very special definitions. The exact lengths are subject to short- and medium-term periodic fluctuations, therefore mean values are given below. These, too, are subject to long-term ("secular") changes, so a reference date must be given for greater accuracy. In the following this is the standard epoch J2000.0 .
- Tropical year
- Since 1955, the new definition applies, according to which the tropical year is the period in which the mean length of the sun increases by 360 °. This is slightly shorter than according to the older definition than the time from one vernal equinox to the next until the earth's axis has the same angle to the sun again, i.e. a complete (apparent) orbit of the sun around the earth. Every solar calendar "should" follow the tropical year, as it describes the seasonal year.
Duration 2000.0: 365.24219052 days = 365 d 5 h 48 min 45.261 s
- Sidereal year
- The time for one orbit of the earth around the sun in relation to a fixed direction in space, that is a complete orbit relative to a fixed star . The sidereal year differs from the tropical year because the earth's axis slowly changes direction ( precession ) .
Duration 2000.0: 365.2563604167 days = 365 d 6 h 9 min 9.54 s
- Anomalous year
- The time between two successive perihelion passages of the earth, i.e. from one point closest to the sun to the next. It is about 5 minutes longer than the sidereal year, because the perihelion of the earth shifts every year ( perihelion rotation ) .
Duration 2000.0: 365.259635864 days = 365 d 6 h 13 min 52.539 s
In principle, the time span between two repetitions of an event that is related to the orbit of any astronomical object around its central object, i.e. each complete revolution, is called the year . One orbit of the earth around the sun is in this sense an earth year .
- A sidereal Mercury year, for example, lasts just under 88 days, a Martian year approx. 687 days and that of Pluto 90,465 days, i.e. 248 years. Here the term 'year' is used synonymously with orbit period . In the case of moons , however, the orbit period is called a month .
- the heliacal year is the time span between two successive heliacal rising of a fixed star. The length and the beginning of such a year depends on the latitude and position of the star.
- The eclipse year (also called the draconian year ) is the time interval between two passes of the sun through the same lunar node . It is related to solar and lunar eclipses . The length is about 346.62 days = 346 d 15 h
- Platonic year is a name for the cycle of precession : It is the time of one complete revolution of the earth's axis on the cone mantle, which is described by precession and lasts about 25,700 to 25,800 years
- The galactic year is the complete orbit of the sun - and our planetary system - around the galactic center . It lasts about 220–240 million years.
Independently of this, the term “year” is also used as a measure of time in astronomy. In this case, it means a period of 365.25 days by 86400 seconds , the average length of a year in the Julian calendar . The reason for this is that, on the one hand, this unit corresponds very precisely to the duration of a solar year and, on the other hand, it can easily be calculated. The units Julian century (36525 days) and Julian millennium are also used for long-term calculations . However, that doesn't mean that astronomers would use the Julian calendar. For dates, they use the common civil (i.e. Gregorian) calendar or the Julian date .
In another cultural context
- school year
- The amount of time it takes a student to get from one class to the next.
In the legal sense, a school year always begins on a certain reference date (around August 1st in some parts of Germany). For the student, a school year usually ends with the start of the long vacation .
- Academic year or academic year
- It is used to divide the study time and usually consists of either two semesters or three trimesters .
The academic year begins on the first day of the winter semester .
- Sabbatical - a year of part-time work or time off from work
- Practical year - part of medical training
In contrast to the other definitions, some details refer to individual chronological key data over the years , i.e. certain personal events. These are not based on the cyclical time calculation of the calendar, but on the linear time calculation of a human life .
- It is used to indicate their age and begins with the birthday . The year of birth is the calendar year in which the birthday falls, the year of death or death is the calendar year of departure.
- Year of instruction or training
- The school year (also called school year for short ) refers to the class in which a student goes. A similar use is also found for the academic year as the time that has elapsed since enrollment . The apprenticeship year denotes the time since entering commercial training .
After nine years of school attendance, compulsory schooling is fulfilled. Twelve (in Germany sometimes thirteen) years of school attendance are the prerequisite for higher education entrance qualification . The minimum length of study varies according to the subject and university system . Most apprenticeships require three years of apprenticeship , which is concluded with the journeyman's examination .
- Year of marriage
- The years a marriage has lasted. It starts with the wedding .
Years that serve to commemorate a person or to remember an event. This includes the reference dates of the annual calculation of some calendar systems ( dynastic calendars ) after the accession of a ruler, in the broader sense the year one of most calendar systems.
- Commemorative year
- Years dedicated to the birth or anniversary of the death of an important person.
The year one ( the birth of Christ ) of our calendar, but also the Mozart year 2006 for the 250th birthday of Wolfgang Amadeus Mozart or the Paulus year 2008/2009 for the 2000 year celebration of the birth of Paulus of Tarsus .
- Year of remembrance
- These relate to historical events with a defining cultural impact.
For example the Olympics as the basis of the oldest Greek calendar, or the Einstein year 2005 on the 100th anniversary of the first appearance of the theory of relativity , or 1000 years of Austria in 1996 after the first known documentary mention of the name.
- Anniversary year
- However, it is also customary to specify special years for a certain anniversary - a “round” anniversary , a selected number of years that have passed since then.
Examples are also: The jubilee year of medieval Christianity, the golden wedding (as the 50th year of marriage ), or the jubilee of a monarch on the throne .
The use of the word anniversary year in connection with reports on the commemorative year at the beginning of the First World War is perceived as a lack of taste or thoughtlessness in view of the consequences of this war.
- Theme year
- In recent times it has also become popular to devote years to a certain socio-cultural aspect in order to give this special attention.
In addition to some of the years already mentioned, this also includes designations such as the International Years proclaimed by the UN (e.g. the year of the child 1979 or the year of freshwater 2003), but also customs such as the bird of the year (e.g. the Year of Archeopteryx 1990, Switzerland) or the special celebration of the secular years that close a century (such as the Millennium 2000). For the Roman Catholic Church , the popes of recent times proclaimed various theme years, such as John Paul II 2005 a year of the Eucharist , Benedict XVI. 2012/2013 a year of faith . - Events that extend over several years are often divided into themed years, such as the council anniversary in Konstanz with its theme years from 2014 to 2018: "5 years - 5 heads - 5 topics".
|Physical quantity (s)
|Time , span of time
|In SI units
The Julian year is a unit of time derived from the year term and corresponds to a time of exactly 365.25 days. It corresponds to the mean value of the year lengths in the Julian calendar and, in contrast to the Julian calendar year, is an exact, constant unit of measurement. It is used in the field of astronomy when there is generally talk of a "year".
Years are combined into a decade ( decade ), century ( hectode ), millennium ( millennium ). Decade millennium ( decamillennium ), century millennium ( hectamillennium ). In the natural sciences, especially in geology and cosmology , periods of time measured in years are also specified using the prefixes for units of measurement :
- ka (also in English-speaking kyr ) is the abbreviation for a millennium ( kilo annum ).
- Ma (in the English language also Myr ) is the abbreviation for a million years ( mega annum ).
- Ga (in the English language and Gyr ) is the abbreviation for a billion years ( giga annum ).
Year and day
Year and day is a medieval legal term. This is the maximum period according to the old law of things. It was created by adding a number of days to the annual period after the local practice.
- Astronomical Almanac Online Glossary 
- Entry Year 2) Unit symbol , DTV Brockhaus , dtv 1988, 9 Iru-Kle S. 52f.
- DIN 1355-1 , 1.1. Calendar year 1.
- DIN 1355, 1.1.5; ISO 8601 2.2.14; ISO 80000-3 : 2006, Annex C.
- In addition, other normative rules also affect the length of the year: For example, a calendar year would have a different duration locally if the official time zone were changed within the year - historically there have even been cases with years without December 31 on a certain island, with a changeover over the date line , see e.g. B. UTC + 14 .
- DIN 1355 1.3. Calendar week 1.
- DIN 1355 1.3.3.
- IAU: Units