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Encyclopedia > Year

A year (from Old English gēr) 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. JÄ“ra GÄ“r JÄ“ran or Jæran (*jÄ“2ram; Gothic jÄ“r, Anglo-Frisian /yÄ“r/, Old High German and Old Saxon jār, Old Norse ār) harvest, (good) year is the reconstructed Proto-Germanic name of the j-rune of the Elder Futhark. ... m. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The Sun is the star at the center of the Solar System. ... The eight planets and three dwarf planets of the Solar System. ...

Contents

Calendar year

A calendar year is the time between two dates with the same name in a calendar. According to the Gregorian calendar, the calendar year begins on January 1 and ends on December 31. ... A page from the Hindu calendar 1871-72. ...


Solar calendars usually aim to predict the four seasons, but because the length of individual seasonal years varies significantly, they instead use an astronomical year as a surrogate. For example, the ancient Egyptians used the heliacal rising of Sirius to predict the flooding of the Nile. A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... Khafres Pyramid (4th dynasty) and Great Sphinx of Giza (c. ... The heliacal rising of a star (or other body such as the moon or a planet) occurs when it first becomes visible above the eastern horizon at dawn, after a period where it was hidden below the horizon or when it was just above the horizon but hidden by the... For information on Sirius satellite radio, see Sirius Satellite Radio. ...


The Gregorian calendar aims to keep the vernal equinox on or close to March 21; hence it follows the vernal equinox year. The average length of its year is 365.2425 days. The Gregorian calendar is the most widely used calendar in the world. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... March 21 is the 80th day of the year in the Gregorian calendar (81st in leap years). ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ...


Among solar calendars in wide use today, the Persian calendar is one of the most precise. Rather than being based on numerical rules, the Persian year begins on the day (for the time zone of Tehran) on which the vernal equinox actually falls, as determined by precise astronomical computations. The Iranian calendar (Persian: ‎) also known as Persian calendar or the Jalāli Calendar is a solar calendar currently used in Iran and Afghanistan. ... This article does not cite its references or sources. ...


No astronomical year has an integer number of days or lunar months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years. Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... A leap year (or intercalary year) is a year containing an extra day (or, in case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. ...


In the Julian calendar, the average length of a year was 365.25 days. This is still used as a convenient time unit in astronomy, see below. The Julian calendar was introduced in 46 BC by Julius Caesar and came into force in 45 BC (709 ab urbe condita). ...


Seasonal year

A 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, the flowering of a species of plant, the first frost, or the first scheduled game of a certain sport. All of these events can have wide variations of more than a month from year to 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. ... This article or section is in need of attention from an expert on the subject. ... Look up Month in Wiktionary, the free dictionary. ...


Academic year

An academic year refers to the annual period during which a student attends school or college. An academic term is a division of an academic year, the time during which a school, college or university holds classes. ...


The school year can be divided up in various ways, two of which are most common in North American educational systems. (1) Many schools divide the academic year into three roughly equal-length quarters (called terms in the UK), more or less coinciding with autumn, winter, and spring. A somewhat shortened summer session, not usually considered part of the regular academic year, is attended by students on a voluntary or elective basis. (2) Other schools break the year into two main semesters, a first (typically August through December) and a second (January through May). Each of these main semesters is split in half and each of the halves is referred to as a quarter. There is also an elective summer session.


In the southern hemisphere the academic year is the same as the calendar year and so the academic year is just referred to as the year.


Astronomical years

Julian year

The Julian year, as used in astronomy and other sciences, is a time unit defined as exactly 365.25 days. This is the normal meaning of the unit "year" (symbol "a" from the Latin annus, annata) used in various scientific contexts. The Julian century of 36,525 days and the Julian millennium of 365,250 days are used in astronomical calculations. Fundamentally, expressing a time interval in Julian years is a way to precisely specify how many days (not how many "real" years), for long time intervals where stating the number of days would be unwieldy and unintuitive. For the distance unit light-year, by convention the Julian year is used in the computation. In astronomy, a Julian year is a unit of time defined as exactly 365. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ...


Sidereal year

The sidereal year is the time for the Earth to complete one revolution of its orbit, as measured in a fixed frame of reference (such as the fixed stars, Latin sidus). Its duration in SI days of 86,400 SI seconds each is on average: The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ... Look up si, Si, SI in Wiktionary, the free dictionary. ...

365.256 363 051 days (365 d 6 h 9 min 9 s) (at the epoch J2000.0 = 2000 January 1 12:00:00 TT).

It has been suggested that this article or section be merged into Julian epoch. ... Terrestrial Time (TT) is the modern time standard for time on the surface of the Earth. ...

Tropical year

A tropical year is the time for the Earth to complete one revolution with respect to the framework provided by the intersection of the ecliptic (the plane of the orbit of the Earth) and the plane of the equator (the plane perpendicular to the rotation axis of the Earth). Because of the precession of the equinoxes, this framework moves slowly westward along the ecliptic with respect to the fixed stars (with a period of about 26,000 tropical years); as a consequence, the Earth completes this year before it completes a full orbit as measured in a fixed reference frame. Therefore a tropical year is shorter than the sidereal year. The exact length of a tropical year depends on the chosen starting point: for example the vernal equinox year is the time between successive vernal equinoxes. The mean tropical year (averaged over all ecliptic points) is: A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... Precession of the equinoxes refers to the precession of the Earths axis of rotation. ...

365.242 189 67 days (365 d 5 h 48 min 45 s) (at the epoch J2000.0).

Anomalistic year

The anomalistic year is the time for the Earth to complete one revolution with respect to its apsides. The orbit of the Earth is elliptical; the extreme points, called apsides, are the perihelion, where the Earth is closest to the Sun (January 2 in 2000), and the aphelion, where the Earth is farthest from the Sun (July 2 in 2000). A diagram of Keplerian orbital elements. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... January 2 is the second day of the year in the Gregorian calendar. ... 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... July 2 is the 183rd day of the year (184th in leap years) in the Gregorian calendar, with 182 days remaining. ...


Because of gravitational disturbances by the other planets, the shape and orientation of the orbit are not fixed, and the apsides slowly move with respect to a fixed frame of reference. Therefore the anomalistic year is slightly longer than the sidereal year. It takes about 112,000 years for the ellipse to revolve once relative to the fixed stars. The anomalistic year is also longer than the tropical year (which calendars attempt to track) and so the date of the perihelion gradually advances every year. It takes about 21,000 years for the ellipse to revolve once relative to the vernal equinox, thus for the date of perihelion to return to the same place (given a calendar that tracks the seasons perfectly). Gravity is a force of attraction that acts between bodies that have mass. ...


The average duration of the anomalistic year is:

365.259 635 864 days (365 d 6 h 13 min 52 s) (at the epoch J2000.0).

Draconic year

The draconitic year, eclipse year or ecliptic year is the time for the Sun (as seen from the Earth) to complete one revolution with respect to the same lunar node (a point where the Moon's orbit intersects the ecliptic). This period is associated with eclipses: these occur only when both the Sun and the Moon are near these nodes; so eclipses occur within about a month of every half eclipse year. Hence there are two eclipse seasons every eclipse year. The average duration of the eclipse year is: The lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic (which is the apparent path of the Sun across the heavens against the background stars). ... Total eclipse redirects here. ...

346.620 075 883 days (346 d 14 h 52 min 54 s) (at the epoch J2000.0).

This term is sometimes erroneously used to designate the draconic or nodal period of lunar precession, that is the time it takes for a complete revolution of the Moon's ascending node around the ecliptic: 18.612 815 932 Julian years (6798.331 019 days; at the epoch J2000.0). The moons elliptical orbit precesses about once in just under 9 years. ... A Julian year is the length of an average year in the Julian calendar, 365. ...


Fumocy

The full moon cycle or fumocy is the time for the Sun (as seen from the Earth) to complete one revolution with respect to the perigee of the Moon's orbit. This period is associated with the apparent size of the full moon, and also with the varying duration of the synodic month. The duration of one full moon cycle is: The full moon cycle is a cycle of about 14 lunations over which full moons vary in apparent size and age (time since new moon). ... Perigee is the point at which an object in orbit around the Earth makes its closest approach to the Earth. ... Composite image of the Moon as taken by the Galileo spacecraft on 7 December 1992. ... Look up Month in Wiktionary, the free dictionary. ...

411.784 430 29 days (411 d 18 h 49 min 34 s) (at the epoch J2000.0).

Heliacal year

A heliacal year is the interval between the heliacal risings of a star. It equals the sidereal year except for a very minor difference due to the proper motion of the star and the precession of the equinoxes. (To visualise the latter: the constellation Crux which rose and set as seen from the Mediterranean in ancient Greek times, is never above the horizon in current times.) The heliacal rising of a star (or other body such as the moon or a planet) occurs when it first becomes visible above the eastern horizon at dawn, after a period where it was hidden below the horizon or when it was just above the horizon but hidden by the... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... Precession of the equinoxes refers to the precession of the Earths axis of rotation. ... CRUX is a lightweight, i686-optimized Linux distribution targeted at experienced Linux users. ... The Mediterranean Sea is an intercontinental sea positioned between Europe to the north, Africa to the south and Asia to the east, covering an approximate area of 2. ... Note: This article contains special characters. ...


Sothic year

The Sothic year is the interval between heliacal risings of the star Sirius. Its duration is very close to the mean Julian year of 365.25 days. The Sothic cycle or Canicular period is a period of 1461 ancient Egyptian years (of 365 days) or 1460 Julian years (averaging 365. ...


Gaussian year

The Gaussian year is the sidereal year for a planet of negligible mass (relative to the Sun) and unperturbed by other planets that is governed by the Gaussian gravitational constant. Such a planet would be slightly closer to the Sun than Earth's mean distance. Its length is: A Gaussian year is defined as 365. ... Carl Friedrich Gauss expressed the gravitational constant in units of the solar system rather than SI units. ...

365.256 898 3 days (365 d 6 h 9 min 56 s).

Besselian year

The Besselian year is a tropical year that starts when the fictitious mean Sun reaches an ecliptic longitude of 280°. This is currently on or close to 1 January. It is named after the 19th century German astronomer and mathematician Friedrich Bessel. An approximate formula to compute the current time in Besselian years from the Julian day is: A Besselian epoch, named after the German mathematician and astronomer Friedrich Bessel (1784 _ 1846), is an epoch that is based on a Besselian year, which is a tropical year measured at the point where the Suns longitude is exactly 280°. Since 1984, Besselian epochs have been superseded by... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Friedrich Wilhelm Bessel (July 22, 1784 – March 17, 1846) was a German mathematician, astronomer, and systematizer of the Bessel functions (which, despite their name, were discovered by Daniel Bernoulli). ... The Julian day or Julian day number (JDN) is the (integer) number of days that have elapsed since Monday, January 1, 4713 BC in the proleptic Julian calendar [1]. That day is counted as Julian day zero. ...

B = 2,000 + (JD - 2,451,544.53) /365.242189

Great year

The Great year, Platonic year, or Equinoctial cycle corresponds to a complete revolution of the equinoxes around the ecliptic. Its length is about 25,700 years, and cannot be determined precisely as the precession speed is variable. A Great year (also known as a Platonic year or Equinoctial cycle) is the time required for one complete cycle of the precession of the equinoxes: about 25700 years. ...


Galactic year

The Galactic year is the time it takes Earth's solar system to revolve once around the galactic center. It comprises roughly 226 million Earth years. // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... The Galactic Center is the rotational center of the Milky Way galaxy. ...


Variation in the length of the year and the day

The exact length of an astronomical year changes over time. The main sources of this change are:

  1. The precession of the equinoxes changes the position of astronomical events with respect to the apsides of Earth's orbit. An event moving toward perihelion recurs with a decreasing period from year to year; an event moving toward aphelion recurs with an increasing period from year to year.
  2. The gravitational influence of the Moon and planets changes the motion of the Earth from a steady orbit around the Sun.

Tidal drag between the Earth and the Moon and Sun increases the length of the day and of the month; since the apparent mean solar day is the unit with which we measure the length of the year in civil life, the length of the year appears to change. Tidal drag in turn depends on factors such as post-glacial rebound and sea level rise. This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... A separate article treats the phenomenon of tidal resonance in oceanography. ... Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process... Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 8 inches per century (2 mm/year). ...


It is also to be expected that changes in the effective mass of the sun, caused by solar wind and radiation of energy generated by nuclear fusion, could affect the Earth's orbital period over a long time. The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ...


Summary of various kinds of year

  • 346.62 days - a draconitic year in some septenary calendars
  • 353, 354 or 355 days — the lengths of common years in some lunisolar calendars
  • 354.37 days/12 lunar months - the average length of a year in lunar calendars
  • 365 days — a common year in many solar calendars
  • 365.24219 days — a mean tropical year near the year 2000
  • 365.2424 days — a vernal equinox year.
  • 365.2425 days — the average length of a year in the Gregorian calendar
  • 365.25 days — the average length of a year in the Julian calendar
  • 365.2564 days — a sidereal year
  • 366 days — a leap year in many solar calendars
  • 383, 384 or 385 days — the lengths of leap years in some lunisolar calendars
  • 383.9 days/13 lunar months - a leap year in some lunisolar calendars

An average Gregorian year is 365.2425 days = 52.1775 weeks, 8,765.82 hours = 525,949.2 minutes = 31,556,952 seconds (mean solar, not SI). A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... It has been suggested that lunar year be merged into this article or section. ... A common year is a calendar year of exactly 365 days and so is not a leap year. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A leap year (or intercalary year) is a year containing an extra day (or, in case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. ... Look up day in Wiktionary, the free dictionary. ... For the TV station in the Peoria-Bloomington, Illinois market, see WEEK-TV. A week is a unit of time longer than a day and shorter than a month. ... The hour (symbol: h) is a unit of time. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ... Look up second in Wiktionary, the free dictionary. ...


A common year is 365 days = 8,760 hours = 525,600 minutes = 31,536,000 seconds.


A leap year is 366 days = 8,784 hours = 527,040 minutes = 31,622,400 seconds.


An easy to remember approximation for the number of seconds in a year is π×107 seconds.


The 400-year cycle of the Gregorian calendar has 146,097 days and hence exactly 20,871 weeks.


See also Numerical facts about the Gregorian calendar. The Gregorian calendar is the most widely used calendar in the world. ...


See also

Look up Year in
Wiktionary, the free dictionary.

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