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 a year on Mars. In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ... A sun is the star at the center of a solar system. ... A planet (from the Greek πλανήτης, planētēs which means wanderer or more forcefully vagrant, tramp) is an object in orbit around a star that is not a star in its own right. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ...

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 hottest day of the year. 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. ... A season is one of the major divisions of the year, generally based on broad climatic patterns. ... In Egyptian mythology, Month is an alternate spelling for Menthu. ...

Calendar year

A calendar year is the time between two dates with the same name in a calendar. In the Gregorian calendar in common use, the calendar year begins on January 1, and ends on December 31. ... A calendar is a system for naming periods of time, typically days. ...

Solar calendars usually aim to predict the 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). ... Map of Ancient Egypt Ancient Egypt was an organized civilization of the Nile Valley from around 3300 BC until the conquest of Alexander the Great in 332 BC, although recent excavations reveal a cattle-herding society of peoples living in the region as early as 6000 BC. By 4000 BC... 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... This article is about the star. ...

The Gregorian calendar aims to keep the vernal equinox on or close to March 21; hence it follows the vernal equinox year. The Gregorian calendar is the calendar widely used in the Western world. ... Illumination of Earth by Sun on the day of equinox In astronomy, the vernal equinox (spring equinox, March equinox, or northward equinox) is the moment when the sun appears to cross the celestial equator, heading northward. ... 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). ...

No astronomical year has an integer number of days or months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years. Intercalation is the insertion of an extra day 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 month in order to keep the calendar year in sync with an astronomical or seasonal year. ...

A Julian year is exactly 365.25 days. This is the normal meaning of the unit "year" (symbol "a") used in various scientific contexts. The Julian century of 36525 days and the Julian millennium of 365250 days are used in astronomical calculations. A Julian year is the length of an average year in the Julian calendar, 365. ...

Astronomical years

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. ... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ...

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).

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: The J2000. ... This article is about terrestrial time; for other meanings of TT, see TT (disambiguation). ... 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. ... The equator is an imaginary line drawn around a planet, halfway between the poles. ... Precession (also called gyroscopic precession) is the phenomenon by which the axis of a spinning object (e. ...

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

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). 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 is also longer than the tropical year (the basis of Gregorian calendar) and so the date of the perihelion gradually advances every year. It takes 21,000 tropical years for the ellipse to revolve once relative to the fixed stars, or for either apside to advance once through all dates of the Julian or Gregorian year. The average duration of the anomalistic year is: This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... 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 2nd day of the year in the Gregorian Calendar. ... 2000 is 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. ... Gravitation is the tendency of masses to move toward each other. ...

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

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: A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... The lunar nodes are 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 solar eclipse in Zambia, 2001 An eclipse (Greek verb: ecleipo = cease to exist) is an astronomical event that occurs when one celestial object moves into the shadow of another. ...

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

The term is sometimes also used to designate the time it takes for a complete revolution of the Moon's ascending node around the ecliptic: 18.612 815 932 years (6798.331 019 days).

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 anomalistic month. The duration of one full moon cycle is: The full moon cycle (the abbreviation fumocy was introduced by Karl Palmen in the CALNDR-L mailing list in October 2002) is a cycle of about 14 lunations over which full moons vary in apparent size. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... The Galileo spacecraft took this composite image on 7 December 1992 on its way to explore the Jupiter system in 1995-97. ... In Egyptian mythology, Month is an alternate spelling for Menthu. ...

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

A heliacal year is the interval between the heliacal risings of a star. It equals the sidereal year only if the star is on the ecliptic. It differs from the sidereal year for stars north or south of the ecliptic because of the significant angle (23.5°) between Earth's celestial equator and the ecliptic. 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 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. ...

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).

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 number of days that have elapsed since 12 noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC (in the proleptic Julian calendar; or November 24, 4714 BC in the proleptic Gregorian calendar). ...

B = 2000 + (JD - 2451544.53)/365.242189

The Great year, Platonic year, or Equinoctial cycle corresponds to a complete revolution of the equinoxes around the ecliptic. Its length is approximately 25,770.639 22 years (9,412,725 d 23 h 22 min). 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 25,800 years. ... Great Year (or Platonic Year) is a time required for one complete cycle of the precession of the equinoxes, about 25,800 years. ... 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 25,800 years. ...

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 shape of the Earth's orbit.

Tidal drag between the Earth and the Moon and Sun increases the length of the day and of the month. This in turn depends on factors such as continental 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. ... 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 known as isostatic depression. ... Measurement of recent sea level rise from 23 long tide gauge records in geologically stable environments Changes in sea level since the end of the last glacial episode Sea level rise is an increase in sea level. ...

It is also suspected that changes in the effective mass of the sun, caused by nuclear fusion, could have a significant impact on the earth year over time.

Summary of various kinds of year

• 353, 354 or 355 days — the lengths of regular 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; ~31.53 million seconds
• 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; the light year is based on it; it is 31,557,600 seconds
• 365.2564 days — a sidereal year
• 366 days — a leap year in many solar calendars; 31.62 million seconds
• 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 lunisolar calendar is a calendar whose date indicates both the moon phase and the season. ... A lunar calendar is a calendar whose date indicates the moon phase. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... A leap year (or intercalary year) is a year containing an extra day or month in order to keep the calendar year in sync with an astronomical or seasonal year. ... A day is any of several different units of time. ... A week is a unit of time longer than a day and shorter than a month. ... The hour was originally defined in Egypt as 1/24 of a day, based on their duo-decimal numbering system (which counted finger joints on each hand). ... A minute is: a unit of time equal to 1/60th of an hour and to 60 seconds. ... This article is about the unit of time. ...

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.

The 400-year cycle of the Gregorian calendar has 146097 days and hence exactly 20871 weeks.

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

See also

• 1 E7 s
• Jera