Astronomical object

An astronomical object or celestial object is a naturally occurring physical entity, association, or structures that exists in the observable universe.[1] In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.

Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both body and object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its diffuse coma and tail.

Asteroid Ida with its own moon Mimas, a natural satellite of Saturn
C2014 Q2.jpgPlanet Jupiter, a gas giant
The Sun, a G-type star Star Sirius A with white dwarf companion Sirius B Crab Nebula.jpg
Black hole (artist's animation)Vela pulsar, a rotating neutron star
Ghiiiiiiiiiiilobular star clusterPleiades, an open star cluster
The Whirlpool galaxyAbel 2744, Galaxy cluster
The Hubble Ultra-Deep Field 2014 image with an estimated 10,000 galaxies
2MASS LSS chart-NEW Nasa
Selection of astronomical bodies and objects

Galaxy and larger

The universe can be viewed as having a hierarchical structure.[2] At the largest scales, the fundamental component of assembly is the galaxy. Galaxies are organized into groups and clusters, often within larger superclusters, that are strung along great filaments between nearly empty voids, forming a web that spans the observable universe.[3]

The universe has a variety of morphologies, with irregular, elliptical and disk-like shapes, depending on their formation and evolutionary histories, including interaction with other galaxies, which may lead to a merger.[4] Disc galaxies encompass lenticular and spiral galaxies with features, such as spiral arms and a distinct halo. At the core, most galaxies have a supermassive black hole, which may result in an active galactic nucleus. Galaxies can also have satellites in the form of dwarf galaxies and globular clusters.[5]

Within a galaxy

The constituents of a galaxy are formed out of gaseous matter that assembles through gravitational self-attraction in a hierarchical manner. At this level, the resulting fundamental components are the stars, which are typically assembled in clusters from the various condensing nebulae.[6] The great variety of stellar forms are determined almost entirely by the mass, composition and evolutionary state of these stars. Stars may be found in multi-star systems that orbit about each other in a hierarchical organization. A planetary system and various minor objects such as asteroids, comets and debris, can form in a hierarchical process of accretion from the protoplanetary disks that surrounds newly formed stars.

The various distinctive types of stars are shown by the Hertzsprung–Russell diagram (H–R diagram)—a plot of absolute stellar luminosity versus surface temperature. Each star follows an evolutionary track across this diagram. If this track takes the star through a region containing an intrinsic variable type, then its physical properties can cause it to become a variable star. An example of this is the instability strip, a region of the H-R diagram that includes Delta Scuti, RR Lyrae and Cepheid variables.[7] Depending on the initial mass of the star and the presence or absence of a companion, a star may spend the last part of its life as a compact object; either a white dwarf, neutron star, or black hole.

Categories by location

The table below lists the general categories of bodies and objects by their location or structure.

Solar bodies Extrasolar
Simple bodies Compound objects Extended objects
Dwarf planets
Minor planets
Stars (see sections below)
By luminosity / evolution
  • O (blue)
  • B (blue-white)
  • A (white)
  • F (yellow-white)
  • G (yellow)
  • K (orange)
  • M (red)
Stellar groupings
Discs and media
Cosmic scale

See also


  1. ^ Task Group on Astronomical Designations from IAU Commission 5 (April 2008). "Naming Astronomical Objects". International Astronomical Union (IAU). Archived from the original on 2 August 2010. Retrieved 4 July 2010.
  2. ^ Narlikar, Jayant V. (1996). Elements of Cosmology. Universities Press. ISBN 81-7371-043-0.
  3. ^ Smolin, Lee (1998). The life of the cosmos. Oxford University Press US. p. 35. ISBN 0-19-512664-5.
  4. ^ Buta, Ronald James; Corwin, Harold G.; Odewahn, Stephen C. (2007). The de Vaucouleurs atlas of galaxies. Cambridge University Press. p. 301. ISBN 0-521-82048-0.
  5. ^ Astronomical Objects for Southern Telescopes. ISBN 0521318874. Retrieved 13 February 2017.
  6. ^ Elmegreen, Bruce G. (January 2010). "The nature and nurture of star clusters". Star clusters: basic galactic building blocks throughout time and space, Proceedings of the International Astronomical Union, IAU Symposium. 266. pp. 3–13. arXiv:0910.4638. Bibcode:2010IAUS..266....3E. doi:10.1017/S1743921309990809.
  7. ^ Hansen, Carl J.; Kawaler, Steven D.; Trimble, Virginia (2004). Stellar interiors: physical principles, structure, and evolution. Astronomy and astrophysics library (2nd ed.). Springer. p. 86. ISBN 0-387-20089-4.

External links

20 Camelopardalis

20 Camelopardalis (20 Cam) is a star in the constellation Camelopardalis. Its apparent magnitude is 7.45.

44 Cancri

44 Cancri (44 Cnc) is an orange-to-red star located in the constellation Cancer. It has an apparent magnitude of 8.04 and its radius is about 12.11 R☉.

80 Cancri

80 Cancri (80 Cnc) is a star in the constellation Cancer. Its apparent magnitude is 6.87.

Deep-sky object

Deep-sky object (abbreviated as DSO) is a term designating any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic objects such as star clusters, nebulae and galaxies. This distinction is practical and technical, implying a variety of instruments and techniques appropriate to observation, and does not distinguish the nature of the object itself.

HD 174569

HD 174569 is a spectroscopic binary star system in the equatorial constellation of Aquila.

HD 185435

HD 185435 is a star in the constellation Cygnus. Its apparent magnitude is 6.42.

HD 63399

HD 63399 is an orange giant star located approximately 445 light years away, in the constellation Puppis. Its apparent magnitude is 6.46.

HD 96660

HD 96660 is an orange giant star located approximately 560 light years away, in the constellation Centaurus. Its apparent magnitude is 6.44.

HD 97413

HD 97413 is a white main-sequence star located 293 light years away, in the constellation Centaurus. Its apparent magnitude is 6.27.

HD 98176

HD 98176 is a white main-sequence star approximately 343 light years away, in the constellation Centaurus. Its apparent magnitude is 6.46.

Hypothetical astronomical object

A hypothetical astronomical object is an astronomical object (such as a star, planet or moon) that is believed or speculated to exist or to have existed but whose existence has not been scientifically proven. Such objects have been hypothesized throughout recorded history. For example, in the 5th century BCE, the philosopher Philolaus "defined a hypothetical astronomical object which he called the Central Fire", around which he proposed other celestial bodies (including the Sun) moved.

LHS 2090

LHS 2090 is a red dwarf star of spectral type M6.5V, located in constellation Cancer at 20.8 light-years from Earth.

List of the most distant astronomical objects

This article documents the most distant astronomical objects so far discovered, and the time periods in which they were so classified.

Distances to remote objects, other than those in nearby galaxies, are nearly always inferred by measuring the cosmological redshift of their light. By their nature, very distant objects tend to be very faint, and these distance determinations are difficult and subject to errors. An important distinction is whether the distance is determined via spectroscopy or using a photometric redshift technique. The former is generally both more precise and also more reliable, in the sense that photometric redshifts are more prone to being wrong due to confusion with lower redshift sources that have unusual spectra. For that reason, a spectroscopic redshift is conventionally regarded as being necessary for an object's distance to be considered definitely known, whereas photometrically determined redshifts identify "candidate" very distant sources. Here, this distinction is indicated by a "p" subscript for photometric redshifts.

NGC 1746

NGC 1746 is an object in the constellation Taurus that was described in 1863 by Heinrich Louis d'Arrest and as a result was recorded in the New General Catalogue (NGC). Previously, the object was classified as an open cluster; however, it was shown through more recent observations that it is a random formation of stars in Earth's sky, an asterism. NGC 1746 has an apparent brightness of 6.1 and an apparent size of about 40'.

NGC 1807

NGC 1807 is a random formation of stars (an asterism) at the border of the constellations Taurus and Orion near the open cluster NGC 1817. NGC 1807 has an apparent size of 17' and an apparent magnitude of 7.0.

NGC 305

NGC 305 is an asterism in the constellation Pisces, discovered on October 17, 1825 by the British astronomer John Herschel.

It is uncertain if the stars are related to one another, but the brightest member, TYC 608-677-2, is a G3V main-sequence star 1330 ± 400 light years away, with a proper motion of 13.8 ± 2.0 mas/yr, or 26.7 ± 4.0 km/s relative to the Sun.

Planetary objects proposed in religion, astrology, ufology and pseudoscience

There are a number of planets or moons whose existence is not supported by scientific evidence, but are proposed by various astrologers, pseudoscientists, conspiracy theorists, or certain religious groups.

RU Andromedae

RU Andromedae is a variable star in the constellation of Andromeda. It is classified as a semiregular variable pulsating giant star, and varies from an apparent visual magnitude of 14.5 at minimum brightness to a magnitude of 9.9 at maximum brightness, with a period of approximately 238.3 days.


A super-Neptune is an astronomical object that is more massive than the planet Neptune. These planets are generally described as being around 5–7 times as large as Earth with estimated masses of 20–80 M⊕, beyond this they are generally referred to as gas giants.

There have been relatively few discoveries of this kind of planets. Known examples include Kepler-101b, HAT-P-11b, and K2-33b.

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