Astronomical object

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Astronomical object
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{{short description|Physical body of astronomically-significant size, mass, or role; naturally occurring in the universe}}{{About|naturally occurring objects|artificial objects|Satellite}}{{Redirect2|Celestial object|Celestial body|other uses|Celestial (disambiguation){{!}}Celestial}}{| class="infobox" style="width: 300px;"|{| style="background: #aaa; white-space: nowrap;" cellpadding=0 cellspacing=0
x120pxalt=Asteroid Ida with its own moon) (File:Mimas Cassini.jpglink=Mimas (moon)|alt=Mimas, a natural satellite of Saturn)
(File:C2014 Q2.jpglink=C/2014 Q2 (Lovejoy)) (File:Portrait of Jupiter from Cassini.jpglink=Jupiter|alt=Planet Jupiter, a gas giant)
(File:The Sun by the Atmospheric Imaging Assembly of NASA's Solar Dynamics Observatory - 20100819.jpglink=Sunx97pxalt=Star Sirius A with white dwarf companion Sirius B) (File:Crab Nebula.jpglink=Crab Nebula)
(File:BlackHole Lensing.giflink=Black holex129pxalt=Vela pulsar, a rotating neutron star)
(File:A Swarm of Ancient Stars - GPN-2000-000930.jpglink=Messier 80x122pxalt=Pleiades, an open star cluster)
(File:Messier51 sRGB.jpglink=Whirlpool galaxyx122pxalt=Abel 2744, Galaxy cluster)
(File:NASA-HS201427a-HubbleUltraDeepField2014-20140603.jpglink=Hubble Ultra-Deep Fieldx93px|alt=Map of galaxy superclusters and filaments)
|Selection of astronomical bodies and objects
An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the observable universe.WEB, Naming Astronomical Objects,weblink Task Group on Astronomical Designations from IAU Commission 5, April 2008, International Astronomical Union (IAU), 4 July 2010,weblink" title="">weblink 2 August 2010, no, 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.

Galaxy and larger

The universe can be viewed as having a hierarchical structure.BOOK, Jayant V., Narlikar, 1996, Elements of Cosmology, Universities Press, 81-7371-043-0,weblink 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.BOOK, Lee, Smolin, 1998, 35, The life of the cosmos, Oxford University Press US, 0-19-512664-5, 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.BOOK, Buta, Ronald James, Corwin, Harold G., Odewahn, Stephen C., 301, 2007, The de Vaucouleurs atlas of galaxies, Cambridge University Press, 0-521-82048-0, 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.BOOK,weblink Astronomical Objects for Southern Telescopes, 0521318874, 13 February 2017,

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.CONFERENCE, Elmegreen, Bruce G., 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, 3–13, January 2010, 10.1017/S1743921309990809, 2010IAUS..266....3E, 0910.4638, 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.BOOK
, Carl J., Hansen, Kawaler, Steven D., Trimble, Virginia
, 86, Stellar interiors: physical principles, structure, and evolution
, Astronomy and astrophysics library
, 2nd, Springer, 2004
, 0-387-20089-4, 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

{{See also|Lists of astronomical objects}}{{See also|List of Solar System objects by size}}The table below lists the general categories of bodies and objects by their location or structure.{| class="wikitable" cellspacing=0 cellpadding=0 style="white-space: nowrap;"! rowspan=2 valign="middle"| Solar bodies! colspan=3 | Extrasolar
! Simple bodies! Compound objects! Extended objects
valign="top"|Solar System Planets Dwarf planets Minor planets |Exoplanets Brown dwarfs Stars {{small|(see sections below)}} By luminosity / evolutionCompact stars By peculiar stars Variables – ExtrinsicVariables – Intrinsic By spectral types
  • (:Category:O-type stars|O) {{small|(blue)}}
  • (:Category:B-type stars|B) {{small|(blue-white)}}
  • (:Category:A-type stars|A) {{small|(white)}}
  • (:Category:F-type stars|F) {{small|(yellow-white)}}
  • (:Category:G-type stars|G) {{small|(yellow)}}
  • (:Category:K-type stars|K) {{small|(orange)}}
  • (:Category:M-type stars|M) {{small|(red)}}
|Systems Binary stars Stellar groupings Galaxies |Discs and media Nebulae Cosmic scale

See also



External links

{{commons category|Astronomical objects}} {{Authority control}}

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M.R.M. Parrott