Astronomical object

"Celestial object" and "Celestial body" redirect here. For other uses, see Celestial (disambiguation).

This article is about naturally occurring objects. For artificial objects, see Satellite.

Selection of astronomical objects

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. The term astronomical object is sometimes used interchangeably with astronomical body. Typically, an astronomical (celestial) body refers to a single, cohesive structure that is bound together by gravity (and sometimes by electromagnetism). Examples include the asteroids, moons, planets and the stars. Astronomical objects are gravitationally bound structures that are associated with a position in space, but may consist of multiple independent astronomical bodies or objects. These objects range from single planets to star clusters, nebulae or entire galaxies. A comet may be described as a body, in reference to the frozen nucleus of ice and dust, or as an object, when describing the nucleus with its diffuse coma and tail.

The universe can be viewed as having a hierarchical structure. At the largest scales, the fundamental component of assembly is the galaxy, which are assembled out of dwarf galaxies. The 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. Galaxies and dwarf galaxies have a variety of morphologies, with the shapes determined by their formation and evolutionary histories, including interaction with other galaxies. Depending on the category, a galaxy may have one or more distinct features, such as spiral arms, a halo and a nucleus. 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.

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. 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. 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

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

Solar bodies	Extrasolar
	Simple bodies	Compound objects	Extended objects
Solar System Giant planet Gas giant Ice giant Heliosphere Oort cloud Meteoroid Micrometeoroid Meteor Bolide Moons Minor planets (see below) Asteroids Dwarf planets Moons Planets (see below) Ring system Trans-Neptunian objects Small Solar System body Comets Planetesimal Sun Planets Mercury Venus Earth – Moon Mars – moons Jupiter – moons Saturn – moons Uranus – moons Neptune – moons Dwarf planets Pluto – moons Eris – Dysnomia Ceres Makemake Haumea – moons Others Minor planets Vulcanoids Apoheles Near-Earth objects PHO Arjunas Atens Apollos Amors Mars-crossers Asteroid belt (families) Alindas Cybeles Eos Floras Hildas Hungarias Hygieas Koronis Marias Nysas Pallas Phocaeas Themis Vesta Trojans Earth Mars Jupiter Uranus Neptune Centaurs Damocloids Kuiper belt objects Classical KBOs Resonant TNOs Plutinos (2:3) Twotinos (1:2) Scattered disc objects Detached objects Sednoid	Exoplanets Chthonian (theoret.) Earth analog Eccentric Jupiter Hot Jupiter Hot Neptune Interstellar Ocean (theoret.) Pulsar planet Rogue planet Super-Earth Trojan (theoret.) Brown dwarfs Types M  · L  · T  · Y Sub-brown dwarfs Stars (see sections below) Stellar classification Stellar population III, II, I Peculiar star Stellar evolution Variable star Compact star By luminosity / evolution Protostar Young stellar object Pre-main-sequence Main sequence Subdwarfs Subgiants Giants Red / Blue Bright giants Supergiants Red / Blue Hypergiants Compact stars (see below) Compact stars Black hole Stellar Intermediate-mass Supermassive GRBs Neutron star Magnetar Pulsar Preon star (hypothet.) Quark star (hypothet.) White dwarf Black dwarf (theoret.) By peculiar stars A-type Peculiar  · Metallic Barium Blue straggler Carbon P Cygni S-type Shell Wolf–Rayet Variables – Extrinsic Rotating Alpha2 CVn Ellipsoidal Eclipsing binaries Algol Beta Lyrae W Ursae Majoris Variables – Intrinsic Pulsating Cepheids W Virginis Delta Scuti RR Lyrae Mira Semiregular Irregular Beta Cephei Alpha Cygni RV Tauri Eruptive variables Flare stars T Tauri FU Orionis RCr Borealis Luminous blue Cataclysmic Symbiotics Dwarf nova Nova Supernova Type: Ia  · Ib/c  · II Hypernova GRBs By spectral types O (blue) B (blue-white) A (white) F (yellow-white) G (yellow) K (orange) M (red)	Systems Planetary Star Stars in general Binary (see below) Triples Higher order Binary stars By observation Optical Visual Astrometric Spectroscopic Eclipsing Close binaries Detached Semidetached Contact X-ray Burster Stellar groupings Star cluster Stellar association Open Globular Hypercompact Constellation Asterism Galaxies Galaxies in general Group and cluster Supercluster By component Bulge Spiral arm Thin disk Thick disk Halo Corona By morphology Spiral Barred spiral Lenticular Elliptical Ring Irregular By size Brightest cluster Giant elliptical Dwarf By type Starburst Dark Active Radio Seyfert Quasar Blazar	Discs and media Interplanetary Dust cloud Medium Magnetic field Stellar disc Accretion Circumstellar Protoplanetary Debris Interstellar Cloud Medium Intergalactic Dust Medium Nebulae Emission Planetary Supernova remnant Plerion H II region Reflection Dark nebulae Molecular cloud Bok globule Proplyd H I region Cosmic scale CMB Cosmic string (hypothet.) Dark matter (hypothet.) MACHO WIMP Domain wall (hypothet.) Dust Filament Void

See also

• International Astronomical Naming Commission
• List of light sources
• List of Solar System objects
• Lists of astronomical objects

External links

Media related to at Wikimedia Commons

• SkyChart, Sky & Telescope
• Monthly skymaps for every location on Earth