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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. 

51 relations: Angle, Angular distance, Astronomical object, Axial precession, Brady Haran, Celestial coordinate system, Celestial equator, Celestial navigation, Celestial pole, Celestial sphere, Colure, Declination, Degree (angle), Degree symbol, Dorado, Draco (constellation), Earth, Earth's rotation, Ecliptic, Ecliptic coordinate system, Epoch (astronomy), Equator, Equatorial coordinate system, Equatorial mount, Equinox, Equinox (celestial coordinates), First Point of Aries, Geographic coordinate system, Hipparchus, Horizon, Hour angle, Hour circle, John Flamsteed, Latitude, Longitude, Meridian (astronomy), Minute and second of arc, Orbital pole, Perpendicular, Pisces (constellation), Polaris, Right angle, Setting circles, Sexagesimal, Sidereal time, Star, Star catalogue, Sun, Telescope, Terrestrial Time, ... Expand index (1 more) »

## Angle

In plane geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.

## Angular distance

In mathematics (in particular geometry and trigonometry) and all natural sciences (e.g. astronomy and geophysics), the angular distance (angular separation, apparent distance, or apparent separation) between two point objects, as viewed from a location different from either of these objects, is the angle of length between the two directions originating from the observer and pointing toward these two objects.

## Astronomical object

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

## Axial precession

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

Brady John Haran (born 18 June 1976) is an Australian-born British independent filmmaker and video journalist who is known for his educational videos and documentary films produced for BBC News and his YouTube channels, the most notable being Periodic Videos and Numberphile.

## 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.

## Celestial equator

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

Celestial navigation, also known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position.

## Celestial pole

The north and south celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere.

## Celestial sphere

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

## Colure

Colure, in astronomy, is either of the two principal meridians of the celestial sphere.

## 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.

## Degree (angle)

A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees.

## Degree symbol

The degree symbol (°) is a typographical symbol that is used, among other things, to represent degrees of arc (e.g. in geographic coordinate systems), hours (in the medical field), degrees of temperature, alcohol proof, or diminished quality in musical harmony.

Dorado (English pronunciation) is a constellation in the southern sky.

## Draco (constellation)

Draco is a constellation in the far northern sky.

## Earth

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

## Earth's rotation

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

## 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.

## 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.

## 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.

## Equator

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

## Equatorial coordinate system

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

## 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.

## 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.

## 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.

## First Point of Aries

The First Point of Aries, also known as the Cusp of Aries, is the location of the vernal equinox, used as a reference point in celestial coordinate systems.

## Geographic coordinate system

A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols.

## Hipparchus

Hipparchus of Nicaea (Ἵππαρχος, Hipparkhos) was a Greek astronomer, geographer, and mathematician.

## Horizon

The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not.

## 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.

## 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.

## John Flamsteed

John Flamsteed FRS (19 August 1646 &ndash; 31 December 1719) was an English astronomer and the first Astronomer Royal.

## Latitude

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

## Longitude

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

## 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.

## Minute and second of arc

A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree.

## Orbital pole

An orbital pole is either point at the ends of an imaginary line segment that runs through the center of an orbit (of a revolving body like a planet) and is perpendicular to the orbital plane.

## Perpendicular

In elementary geometry, the property of being perpendicular (perpendicularity) is the relationship between two lines which meet at a right angle (90 degrees).

## Pisces (constellation)

Pisces is a constellation of the zodiac.

## Polaris

Polaris, designated Alpha Ursae Minoris (Ursae Minoris, abbreviated Alpha UMi, UMi), commonly the North Star or Pole Star, is the brightest star in the constellation of Ursa Minor.

## Right angle

In geometry and trigonometry, a right angle is an angle of exactly 90° (degrees), corresponding to a quarter turn.

## 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.

## Sexagesimal

Sexagesimal (base 60) is a numeral system with sixty as its base.

## Sidereal time

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

## Star

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

## Star catalogue

A star catalogue (Commonwealth English) or star catalog (American English), is an astronomical catalogue that lists stars.

## Sun

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

## Telescope

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

## 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.

## University of Nottingham

The University of Nottingham is a public research university in Nottingham, United Kingdom.

## References

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