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# Parsec

A parsec (symbol: pc) is a unit of length used to measure the astronomically large distances to objects outside the Solar System. [1]

96 relations: Absolute magnitude, Andromeda Galaxy, Angular diameter, Angular distance, Approximation, Astrometry, Astronomer, Astronomer Royal, Astronomical object, Astronomical system of units, Astronomical unit, Astronomische Nachrichten, Boötes, Boötes void, Brady Haran, Carl Charlier, Celestial sphere, CfA2 Great Wall, Constellation, Cosmic background radiation, Cosmic distance ladder, Cosmology, Diameter, Earth, European Space Agency, Frank Watson Dyson, Friedrich Bessel, Full-sky Astrometric Mapping Explorer, Gaia (spacecraft), Galactic Center, Galaxy, Galaxy cluster, Galaxy filament, Galaxy group, Giga-, Globular cluster, Goddard Space Flight Center, Herbert Hall Turner, Hercules-Corona Borealis Great Wall, Hipparcos, Hubble's law, Imperial units, International Astronomical Union, International System of Units, Kilo-, Kilometre, Light-year, List of largest cosmic structures, Mega-, Messier 87, ... Expand index (46 more) »

## Absolute magnitude

Absolute magnitude is the measure of intrinsic brightness of a celestial object.

## Andromeda Galaxy

The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth.

## Angular diameter

The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view.

## Angular distance

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

## Approximation

An approximation is anything that is similar but not exactly equal to something else.

## Astrometry

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

## Astronomer

An astronomer is a scientist in the field of astronomy who studies stars, planets, moons, comets, and galaxies, as well as many other celestial objects.

## Astronomer Royal

Astronomer Royal is a senior post in the Royal Households of the United Kingdom.

## Astronomical object

An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that current science has demonstrated to exist in the observable universe.

## Astronomical system of units

The astronomical system of units, formally called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy.

## Astronomical unit

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

## Astronomische Nachrichten

Astronomische Nachrichten (Astronomical Notes), one of the first international journals in the field of astronomy, was founded in 1821 by the German astronomer Heinrich Christian Schumacher.

## Boötes

Boötes is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere.

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## Boötes void

The Boötes void or the Great Void is a huge and approximately spherically shaped region of space, containing very few galaxies.

Brady John Haran (born 18 June 1976) is an Australian independent film-maker and video journalist who is known for his educational videos and documentary films produced for BBC News and for his YouTube channels, such as Numberphile and Periodic Videos.

## Carl Charlier

Carl Vilhelm Ludwig Charlier (April 1, 1862 &ndash; November 5, 1934) was a Swedish astronomer.

## Celestial sphere

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

## CfA2 Great Wall

The Great Wall (also called Coma Wall), sometimes specifically referred to as the CfA2 Great Wall, is an immense galaxy filament.

## Constellation

In modern astronomy, a constellation is a specific area of the celestial sphere as defined by the International Astronomical Union (IAU).

Cosmic background radiation is electromagnetic radiation from the sky with no discernible source.

The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects.

## Cosmology

Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of"), is the study of the origin, evolution, and eventual fate of the universe.

## Diameter

In geometry, the diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle.

## Earth

Earth (also the world, in Greek: Gaia, or in Latin: Terra), is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to accommodate life.

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## European Space Agency

The European Space Agency (ESA; Agence spatiale européenne, ASE; Europäische Weltraumorganisation) is an intergovernmental organisation dedicated to the exploration of space, with 22 member states.

## Frank Watson Dyson

Sir Frank Watson Dyson, KBE, FRS (8 January 1868 – 25 May 1939) was an English astronomer and Astronomer Royal who is remembered today largely for introducing time signals ("pips") from Greenwich, England, and for the role he played in proving Einstein's theory of general relativity.

## Friedrich Bessel

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

## Full-sky Astrometric Mapping Explorer

Full-sky Astrometric Mapping Explorer (or FAME) was a proposed astrometric satellite designed to determine with unprecedented accuracy the positions, distances, and motions of 40 million stars within our galactic neighborhood (distances by stellar parallax possible).

## Gaia (spacecraft)

Gaia is a space observatory of the European Space Agency (ESA) designed for astrometry.

## Galactic Center

The Galactic Center is the rotational center of the Milky Way.

## Galaxy

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas and dust, and dark matter.

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## Galaxy cluster

A galaxy cluster or cluster of galaxies is a structure that consists of anywhere from hundreds to thousands of galaxies bound together by gravity.

## Galaxy filament

The distribution reveals fine, filamentary structures.

## Galaxy group

A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxies larger than groups that are first-order clustering are called galaxy clusters.

## Giga-

Giga is a unit prefix in the metric system denoting a factor of a (short-form) billion (109 or 000).

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## Globular cluster

A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite.

## Goddard Space Flight Center

The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center.

## Herbert Hall Turner

Herbert Hall Turner FRS (13 August 1861, Leeds – 20 August 1930, Stockholm) was a British astronomer and seismologist.

## Hercules-Corona Borealis Great Wall

Hercules-Corona Borealis Great Wall or the Great GRB Wall.

## Hipparcos

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

## Hubble's law

Hubble's law is the name for the observation in physical cosmology that.

## Imperial units

The system of imperial units or the imperial system (also known as British Imperial) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced.

## International Astronomical Union

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

## International System of Units

The International System of Units (Système International d'Unités, SI) is the modern form of the metric system, and is the most widely used system of measurement.

## Kilo-

Kilo (from the Greek χίλιοι, literally a thousand) is a unit prefix in the metric system denoting multiplication by one thousand.

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## Kilometre

The kilometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: km; or) or kilometer (American spelling) is a unit of length in the metric system, equal to one thousand metres (kilo- being the SI prefix for). It is now the measurement unit used officially for expressing distances between geographical places on land in most of the world; notable exceptions are the United States and the United Kingdom where the statute mile is the official unit used.

## Light-year

A light-year (abbreviation: ly), sometimes written light year, is a unit of length used informally to express astronomical distances.

## List of largest cosmic structures

This is a list of the largest known large-scale cosmic structures.

## Mega-

Mega is a unit prefix in the metric system denoting a factor of one million (106 or 000).

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## Messier 87

Messier 87 (also known as Virgo A or NGC 4486, and generally abbreviated to M87) is a supergiant elliptical galaxy in the constellation Virgo.

## Messier object

The Messier objects are a set of over 100 astronomical objects first listed by French astronomer Charles Messier in 1771.

## Metre

The metre, American spelling meter, (from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units (SI).

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## Metric system

The metric system is an internationally agreed decimal system of measurement.

## Mile

The mile is an English unit of length equal to and standardised as exactly 1.609344 kilometres by international agreement in 1959.

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## Milky Way

The Milky Way is the galaxy that contains our Solar System.

## Minute and second of arc

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

## Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society (MNRAS) is a peer-reviewed scientific journal covering research in astronomy and astrophysics.

## Multiplicative inverse

In mathematics, a multiplicative inverse or reciprocal for a number x, denoted by 1/x or x&minus;1, is a number which when multiplied by x yields the multiplicative identity, 1.

## NASA

The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research.

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## Observable universe

The observable universe consists of the galaxies and other matter that can, in principle, be observed from Earth at the present time because light and other signals from these objects has had time to reach the Earth since the beginning of the cosmological expansion.

## Oort cloud

The Oort cloud or Öpik–Oort cloud, named after Dutch astronomer Jan Oort and Estonian astronomer Ernst Öpik, is a theoretical spherical cloud of predominantly icy planetesimals believed to surround the Sun at a distance of up to around.

## Open cluster

An open cluster, also known as galactic cluster, is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age.

## Orders of magnitude (length)

The following are examples of orders of magnitude for different lengths.

## Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

## Particle horizon

The particle horizon (also called the cosmological horizon, the light horizon, or the cosmic light horizon) is the maximum distance from which particles could have traveled to the observer in the age of the universe.

In astronomy, the Pleiades, or Seven Sisters (Messier 45 or M45), is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus.

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## Quasar

Quasars or quasi-stellar radio sources are the most energetic and distant members of a class of objects called active galactic nuclei (AGN).

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## Redshift

In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

## Right triangle

A right triangle (American English) or right-angled triangle (British English) is a triangle in which one angle is a right angle (that is, a 90-degree angle).

## RXJ1242-11

RXJ1242-11 is an elliptical galaxy located approximately 200 megaparsecs (about 650 million light-years) from Earth.

## Sagittarius (constellation)

Sagittarius is one of the constellations of the zodiac.

## Semi-major axis

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.

## Significant figures

The significant figures of a number are digits that carry meaning contributing to its measurement resolution.

## Skinny triangle

A skinny triangle in trigonometry is a triangle whose height is much greater than its base.

## Small-angle approximation

The small-angle approximation is a useful simplification of the basic trigonometric functions which is approximately true in the limit where the angle approaches zero.

## Solar System

The Solar SystemCapitalization of the name varies.

## Space probe

A space probe is a robotic spacecraft that leaves Earth orbit and explores space.

## Speed of light

The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.

## Spiral galaxy

A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae(pp. 124–151) and, as such, forms part of the Hubble sequence.

## Star

A star is a luminous sphere of plasma held together by its own gravity.

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## Subtended angle

In geometry, an angle subtended by an arc, line, or other curve is one whose two rays pass through the endpoints of the arc.

## Sun

The Sun (in Greek: Helios, in Latin: Sol) is the star at the center of the Solar System and is by far the most important source of energy for life on Earth.

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## Supercluster

Superclusters are large groups of smaller galaxy clusters or galaxy groups and are among the largest known structures of the cosmos.

## Supermassive black hole

A supermassive black hole (SMBH) is the largest type of black hole, on the order of hundreds of thousands to billions of solar masses, and is found in the center of almost all massive galaxies.

## Tangent

In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point.

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## Telescope

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

## Trigonometric functions

In mathematics, the trigonometric functions (also called the circular functions) are functions of an angle.

## Trigonometry

Trigonometry (from Greek trigōnon, "triangle" and metron, "measure") is a branch of mathematics that studies relationships involving lengths and angles of triangles.

## United States customary units

United States customary units are a system of measurements commonly used in the United States.

## Units of measurement

A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same physical quantity.

## University of Nottingham

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

## Virgo Cluster

The Virgo Cluster (VC) is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the constellation Virgo.

## Voyager 1

Voyager 1 is a space probe launched by NASA on September 5, 1977.

## 1,000,000,000

1,000,000,000 (one billion, short scale; one thousand million or milliard, yard, long scale) is the natural number following 999,999,999 and preceding 1,000,000,001.

## 61 Cygni

61 Cygni Not to be confused with 16 Cygni, a more distant system containing two G-type stars harboring the gas giant planet 16 Cygni Bb.

## References

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