61 relations: Astronomical nutation, Astronomical object, Astronomical unit, Astronomy, Axial precession, Basis (linear algebra), Cambridge University Press, Cartesian coordinate system, Celestial coordinate system, Celestial equator, Celestial sphere, Culmination, Declination, Distance, Earth, Earth's rotation, Earth-centered inertial, Ecliptic, Ephemeris, Epoch (astronomy), Equator, Equatorial mount, Equinox, Equinox (celestial coordinates), Fixed stars, Fundamental plane (spherical coordinates), Geocentric model, Geographical pole, Handedness, Horizontal coordinate system, Hour angle, Hour circle, International Celestial Reference Frame, Latitude, Longitude, Meridian (astronomy), Meridian circle, Orbit, Orbital mechanics, Orientation (geometry), Origin (mathematics), Plane (geometry), Planet, Polar distance (astronomy), Position of the Sun, Projective geometry, Right ascension, Right-hand rule, Satellite, Setting circles, ..., Sidereal time, Solar System, Solar time, Spherical astronomy, Spherical coordinate system, Star, Star chart, Sun, Telescope, Transparency and translucency, Unit vector. Expand index (11 more) »

## Astronomical nutation

Astronomical nutation is a phenomenon which causes the orientation of the axis of rotation of a spinning astronomical object to vary over time.

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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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## Astronomical unit

The astronomical unit (symbol: au, ua, or AU) is a unit of length, roughly the distance from Earth to the Sun.

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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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## Basis (linear algebra)

In mathematics, a set of elements (vectors) in a vector space V is called a basis, or a set of, if the vectors are linearly independent and every vector in the vector space is a linear combination of this set.

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## Cambridge University Press

Cambridge University Press (CUP) is the publishing business of the University of Cambridge.

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## Cartesian coordinate system

A Cartesian coordinate system is a coordinate system that specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular directed lines, measured in the same unit of length.

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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 equator

The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth.

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## Celestial sphere

In astronomy and navigation, the celestial sphere is an abstract sphere with an arbitrarily large radius concentric to Earth.

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## Culmination

In astronomy, the culmination of a planet, star, or constellation is its transit over an observer's meridian.

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## Declination

In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle.

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## Distance

Distance is a numerical measurement of how far apart objects are.

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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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## Earth's rotation

Earth's rotation is the rotation of Planet Earth around its own axis.

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## Earth-centered inertial

Earth-centered inertial (ECI) coordinate frames have their origins at the center of mass of the Earth.

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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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## 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 (astronomy)

In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.

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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 mount

An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis parallel to the Earth's axis of rotation.

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## Equinox

An equinox is commonly regarded as the moment the plane (extended indefinitely in all directions) of Earth's equator passes through the center of the Sun, which occurs twice each year, around 20 March and 22-23 September.

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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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## Fixed stars

The fixed stars (stellae fixae) comprise the background of astronomical objects that appear to not move relative to each other in the night sky compared to the foreground of Solar System objects that do.

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## Fundamental plane (spherical coordinates)

The fundamental plane in a spherical coordinate system is a plane of reference that divides the sphere into two hemispheres.

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## Geocentric model

In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system) is a superseded description of the universe with Earth at the center.

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## Geographical pole

A geographical pole is either of the two points on a rotating body (planet, dwarf planet, natural satellite, sphere...etc) where its axis of rotation intersects its surface.

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## Handedness

In human biology, handedness is a better, faster, or more precise performance or individual preference for use of a hand, known as the dominant hand; the less capable or less preferred hand is called the non-dominant hand.

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## Horizontal coordinate system

The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane.

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## Hour angle

In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere.

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## Hour circle

In astronomy, the hour circles, which together with declination and distance (from the centre of mass of the planet) locate any celestial object, is the great circle through the object and the two celestial poles.

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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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## Latitude

In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface.

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## Longitude

Longitude, is a geographic coordinate that specifies the east-west position of a point on the Earth's surface.

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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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## Meridian circle

The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir.

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## Orbit

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet.

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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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## Orientation (geometry)

In geometry the orientation, angular position, or attitude of an object such as a line, plane or rigid body is part of the description of how it is placed in the space it occupies.

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## Origin (mathematics)

In mathematics, the origin of a Euclidean space is a special point, usually denoted by the letter O, used as a fixed point of reference for the geometry of the surrounding space.

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## Plane (geometry)

In mathematics, a plane is a flat, two-dimensional surface that extends infinitely far.

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## Planet

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

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## Polar distance (astronomy)

In the celestial equatorial coordinate system Σ(α, δ) in astronomy, polar distance (PD) is an angular distance of a celestial object on its meridian measured from the celestial pole, similar to the way declination (dec, δ) is measured from the celestial equator.

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## Position of the Sun

The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface.

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## Projective geometry

Projective geometry is a topic in mathematics.

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## Right ascension

Right ascension (abbreviated RA; symbol) is the angular distance measured only eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point above the earth in question.

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## Right-hand rule

In mathematics and physics, the right-hand rule is a common mnemonic for understanding orientation conventions for the vector cross product in three dimensions.

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## Satellite

In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit.

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## Setting circles

Setting circles are used on telescopes equipped with an equatorial mount to find astronomical objects in the sky by their equatorial coordinates often used in star charts or ephemerides.

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## Sidereal time

Sidereal time is a timekeeping system that astronomers use to locate celestial objects.

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## Solar System

The Solar SystemCapitalization of the name varies.

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## Solar time

Solar time is a calculation of the passage of time based on the position of the Sun in the sky.

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## Spherical astronomy

Spherical astronomy or positional astronomy is the branch of astronomy that is used to determine the location of objects on the celestial sphere, as seen at a particular date, time, and location on Earth.

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## Spherical coordinate system

In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the radial distance of that point from a fixed origin, its polar angle measured from a fixed zenith direction, and the azimuth angle of its orthogonal projection on a reference plane that passes through the origin and is orthogonal to the zenith, measured from a fixed reference direction on that plane.

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## Star

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.

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## Star chart

A star chart or star map, also called a sky chart or sky map, is a map of the night sky.

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## Sun

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

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## Telescope

A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).

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## Transparency and translucency

In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without being scattered.

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## Unit vector

In mathematics, a unit vector in a normed vector space is a vector (often a spatial vector) of length 1.

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## Redirects here:

Equatorial Coordinates, Equatorial coordinates, RA/Dec.

## References

[1] https://en.wikipedia.org/wiki/Equatorial_coordinate_system