63 relations: Aberration of light, Apsis, Astrometry, Astronomical object, Astronomy, Axial precession, Bede, Celestial coordinate system, Celestial mechanics, Civil time, Constellation, Coordinated Universal Time, Earth, Ecliptic, Ecliptic coordinate system, Ephemeris, Epoch (reference date), Equator, Equatorial coordinate system, Equinox (celestial coordinates), Friedrich Bessel, Gregorian calendar, Hebrew calendar, Heliacal rising, Henry Draper Catalogue, Hipparcos, Infinity, International Astronomical Union, International Atomic Time, International Celestial Reference Frame, International Celestial Reference System, Islamic calendar, ΔT, Julian calendar, Julian day, Julian year (astronomy), Longitude of the ascending node, Lunar calendar, Lunisolar calendar, March equinox, Mean anomaly, Mean longitude, Meridian (astronomy), Midnight, Minor planet, Noon, Orbital elements, Orbital mechanics, Osculating orbit, Perihelion and aphelion, ..., Perturbation (astronomy), Plane of reference, Polynomial, Precession, Proper motion, Semi-major and semi-minor axes, Sirius, SOFA (astronomy), Sun, Terrestrial Time, Universal Time, Year, 5145 Pholus. Expand index (13 more) »

## Aberration of light

The aberration of light (also referred to as astronomical aberration, stellar aberration, or velocity aberration) is an astronomical phenomenon which produces an apparent motion of celestial objects about their true positions, dependent on the velocity of the observer.

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## Apsis

An apsis (ἁψίς; plural apsides, Greek: ἁψῖδες) is an extreme point in the orbit of an object.

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## Astrometry

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.

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## Astronomical object

An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the observable universe.

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## Astronomy

Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.

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## Axial precession

In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis.

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## Bede

Bede (italic; 672/3 – 26 May 735), also known as Saint Bede, Venerable Bede, and Bede the Venerable (Bēda Venerābilis), was an English Benedictine monk at the monastery of St.

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## Celestial coordinate system

In astronomy, a celestial coordinate system is a system for specifying positions of celestial objects: satellites, planets, stars, galaxies, and so on.

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## Celestial mechanics

Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects.

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## Civil time

In modern usage, civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks.

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## Constellation

A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices.

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## Coordinated Universal Time

No description.

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## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

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## Ecliptic

The ecliptic is the circular path on the celestial sphere that the Sun follows over the course of a year; it is the basis of the ecliptic coordinate system.

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## Ecliptic coordinate system

The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions and orbits of Solar System objects.

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## Ephemeris

In astronomy and celestial navigation, an ephemeris (plural: ephemerides) gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times.

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## Epoch (reference date)

In the fields of chronology and periodization, an epoch is an instant in time chosen as the origin of a particular era.

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## Equator

An equator of a rotating spheroid (such as a planet) is its zeroth circle of latitude (parallel).

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## Equatorial coordinate system

The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects.

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## Equinox (celestial coordinates)

In astronomy, equinox is a moment when the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system.

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## Friedrich Bessel

Friedrich Wilhelm Bessel (22 July 1784 – 17 March 1846) was a German astronomer, mathematician, physicist and geodesist.

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## Gregorian calendar

The Gregorian calendar is the most widely used civil calendar in the world.

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## Hebrew calendar

The Hebrew or Jewish calendar (Ha-Luah ha-Ivri) is a lunisolar calendar used today predominantly for Jewish religious observances.

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## Heliacal rising

The heliacal rising or star rise of a star, star cluster, or galaxy occurs annually when it becomes visible above the eastern horizon for a moment before sunrise, after a period of less than a year when it had not been visible.

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## Henry Draper Catalogue

The Henry Draper Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper Extension Charts (HDEC), published from 1937 to 1949 in the form of charts, which gave classifications for 86,933 more stars.

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## Hipparcos

Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993.

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## Infinity

Infinity (symbol) is a concept describing something without any bound or larger than any natural number.

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## International Astronomical Union

The International Astronomical Union (IAU; Union astronomique internationale, UAI) is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy.

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## International Atomic Time

International Atomic Time (TAI, from the French name temps atomique international) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid.

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## International Celestial Reference Frame

In astrometry, an International Celestial Reference Frame (ICRF) is a realization of the International Celestial Reference System (ICRS) using reference celestial sources observed at radio wavelengths.

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## International Celestial Reference System

The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU).

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## Islamic calendar

The Islamic, Muslim, or Hijri calendar (التقويم الهجري at-taqwīm al-hijrī) is a lunar calendar consisting of 12 months in a year of 354 or 355 days.

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## ΔT

In precise timekeeping, ΔT (Delta T, delta-T, deltaT, or DT) is the time difference obtained by subtracting Universal Time (UT) from Terrestrial Time (TT):.

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## Julian calendar

The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar.

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## Julian day

Julian day is the continuous count of days since the beginning of the Julian Period and is used primarily by astronomers.

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## Julian year (astronomy)

In astronomy, a Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of SI seconds each.

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## Longitude of the ascending node

The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space.

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## Lunar calendar

A lunar calendar is a calendar based upon the monthly cycles of the Moon's phases (synodic months), in contrast to solar calendars, whose annual cycles are based only directly upon the solar year.

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## Lunisolar calendar

A lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year.

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## March equinox

The March equinox or Northward equinox is the equinox on the Earth when the subsolar point appears to leave the southern hemisphere and cross the celestial equator, heading northward as seen from Earth.

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## Mean anomaly

In celestial mechanics, the mean anomaly is an angle used in calculating the position of a body in an elliptical orbit in the classical two-body problem.

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## Mean longitude

Mean longitude is the ecliptic longitude at which an orbiting body could be found if its orbit were circular and free of perturbations.

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## Meridian (astronomy)

In astronomy, the meridian is the great circle passing through the celestial poles, the zenith, and the nadir of an observer's location.

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## Midnight

Midnight is the transition time from one day to the next – the moment when the date changes.

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## Minor planet

A minor planet is an astronomical object in direct orbit around the Sun (or more broadly, any star with a planetary system) that is neither a planet nor exclusively classified as a comet.

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## Noon

Noon (also midday or noon time) is 12 o'clock in the daytime, as opposed to midnight.

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## Orbital elements

Orbital elements are the parameters required to uniquely identify a specific orbit.

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## Orbital mechanics

Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft.

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## Osculating orbit

In astronomy, and in particular in astrodynamics, the osculating orbit of an object in space at a given moment in time is the gravitational Kepler orbit (i.e. ellipse or other conic) that it would have about its central body if perturbations were not present.

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## Perihelion and aphelion

The perihelion of any orbit of a celestial body about the Sun is the point where the body comes nearest to the Sun.

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## Perturbation (astronomy)

In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body.

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## Plane of reference

In celestial mechanics, the plane of reference (or reference plane) is the plane used to define orbital elements (positions).

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## Polynomial

In mathematics, a polynomial is an expression consisting of variables (also called indeterminates) and coefficients, that involves only the operations of addition, subtraction, multiplication, and non-negative integer exponents of variables.

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## Precession

Precession is a change in the orientation of the rotational axis of a rotating body.

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## Proper motion

Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.

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## Semi-major and semi-minor axes

In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the widest points of the perimeter.

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## Sirius

Sirius (a romanization of Greek Σείριος, Seirios,."glowing" or "scorching") is a star system and the brightest star in the Earth's night sky.

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## SOFA (astronomy)

The SOFA (Standards of Fundamental Astronomy) software libraries are a collection of subroutines that implement official International Astronomical Union algorithms for astronomical computations.

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## Sun

The Sun is the star at the center of the Solar System.

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## Terrestrial Time

Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth.

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## Universal Time

Universal Time (UT) is a time standard based on Earth's rotation.

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## Year

A year is the orbital period of the Earth moving in its orbit around the Sun.

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## 5145 Pholus

5145 Pholus (from Φόλος) provisional designation, is an eccentric centaur in the outer Solar System, approximately 180 kilometers in diameter, that crosses the orbit of both Saturn and Neptune.

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## Redirects here:

1875.0, 1900.0, 1950.0, 2000.0, Astronomical epoch, B1875, B1875.0, B1900, B1900.0, B1950, B1950.0, B2000.0, Besselian epoch, Besselian year, Epoch astronomy, Epochal moment, J1900, J1900.0, J1950, J1950.0, J2000, J2000.0, Julian epoch, Standard epoch 2000.

## References

[1] https://en.wikipedia.org/wiki/Epoch_(astronomy)