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In
astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathematics, phys ...
, an astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the
observable universe The observable universe is a ball-shaped region of the universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang th ...
. In
astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathematics, phys ...
, 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 system A planetary system is a set of gravity, gravitationally bound non-Star, stellar objects in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems m ...
s,
star cluster Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of hundreds to millions of old stars which are gravitationally bound, while open clusters are more loosely clustered ...
s,
nebula A nebula ( for 'cloud' or 'fog'; pl. nebulae, nebulæ or nebulas) is a distinct body of s (which can consist of , , , ; possibly as ). Originally, the term was used to describe any diffused , including beyond the . The , for instance, was once ...

nebula
e, and
galaxies A galaxy is a gravitationally bound system of star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to ...

galaxies
, while
asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observ ...

asteroid
s,
moons A natural satellite, or moon, is, in the most common usage, an astronomical body that orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet around a star or ...

moons
,
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
s, and
star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

star
s are astronomical bodies. A
comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...

comet
may be identified as both body and object: It is a ''body'' when referring to the frozen
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
of ice and dust, and an ''object'' when describing the entire comet with its diffuse
coma A coma is a deep state of prolonged unconsciousness Unconsciousness is a state which occurs when the ability to maintain an consciousness, awareness of self and environment is lost. It involves a complete, or near-complete, lack of responsive ...
and
tail The tail is the section at the rear end of certain kinds of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotrop ...

tail
.


Galaxy and larger

The
universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development ...

universe
can be viewed as having a hierarchical structure. At the largest scales, the fundamental component of assembly is the
galaxy A galaxy is a gravitation Gravity (), or gravitation, is a natural phenomenon by which all things with mass Mass is both a property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or ...

galaxy
. Galaxies are organized into groups and clusters, often within larger
superclusters A supercluster is a large group of smaller galaxy clusters or galaxy groups; it is among the largest known structures of the universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, ...
, that are strung along great filaments between nearly empty
voids Void may refer to: Science, engineering, and technology * Void (astronomy), the spaces between galaxy filaments that contain no galaxies * Void (composites), a pore that remains unoccupied in a composite material * Void, synonym for vacuum, a s ...
, forming a web that spans the observable universe. Galaxies have a variety of morphologies, with
irregular Something that is irregular does not follow the expected pattern; not even or balanced in shape or arrangement; abnormal. The term is used in many different fields, with various meanings. Accounting * Accounting irregularity Astronomy * Irreg ...
, elliptical and disk-like shapes, depending on their formation and evolutionary histories, including
interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect. Closely related terms are interac ...
with other galaxies, which may lead to a
merger In corporate finance Corporate finance is the area of finance that deals with sources of funding, the capital structure of corporations, the actions that managers take to increase the Value investing, value of the firm to the shareholders, ...
. Disc galaxies encompass lenticular and
spiral galaxies Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''
with features, such as
spiral arms Spiral galaxies form a class of galaxy originally described by Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic as ...
and a distinct
halo Halo generally refers to: * Halo (optical phenomenon) * Halo (religious iconography), a glow or ring of light around a head or person in art or a ring above one's head * Halo (franchise), ''Halo'' (franchise), a video game franchise Halo or HALO ...
. At the core, most galaxies have a
supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. ...

supermassive black hole
, which may result in an
active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy A galaxy is a gravitation Gravity (), or gravitation, is a natural phenomenon by which all things with mass Mass is both a property Property (''la ...
. Galaxies can also have satellites in the form of
dwarf galaxies Dwarf or dwarves may refer to: Common uses *Dwarf (folklore), a being from Germanic mythology and folklore * Dwarf, a person or animal with dwarfism * Dwarf to describe a small person Arts, entertainment, and media Fictional entities *Dwarf (Du ...
and
globular cluster A globular cluster is a sphere, spherical collection of stars. wiktionary:globular, Globular clusters are very tightly bound by gravity, with a high concentration of stars towards their centers. Their name is derived from Latin —a small sphere. ...
s.


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. 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 disk A protoplanetary disk is a rotating circumstellar disc A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accumulation of matter composed of gas, Cosmic dust, dust, planetesimals, asteroids, or collision fragments i ...

protoplanetary disk
s that surround newly formed stars. The various distinctive types of stars are shown by the
Hertzsprung–Russell diagram The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The ...
(H–R diagram)—a plot of absolute stellar luminosity versus surface temperature. Each star follows an
evolutionary track In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses m ...
across this diagram. If this track takes the star through a region containing an
intrinsic variable A variable star is a star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many ot ...
type, then its physical properties can cause it to become a
variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: ...
. An example of this is the
instability strip Image:HR-diag-instability-strip.svg, 350px The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Ph ...
, a region of the H-R diagram that includes
Delta Scuti Delta Scuti (δ Sct, δ Scuti) is a giant star in the southern constellation Scutum (constellation), Scutum. With an apparent visual magnitude of 4.72, it is the List of stars in Scutum, fifth-brightest star in this small and otherwise undi ...
,
RR Lyrae RR Lyrae is a variable star in the Lyra constellation, figuring in its west near to Cygnus (constellation), Cygnus. As the brightest star in its class, it became the wikt:eponym, eponym for the RR Lyrae variable class of stars and it ha ...
and
Cepheid variable A Cepheid variable () is a type of star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the ...
s. The evolving star may eject some portion of its atmosphere to form a nebula, either steadily to form a
planetary nebula A planetary nebula (PN, plural PNe), is a type of emission nebula An emission nebula is a nebula " from the Eagle Nebula. Evidence from the Spitzer Telescope suggests that the pillars may already have been destroyed by a supernova explos ...

planetary nebula
or in a
supernova A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a powerful and luminous stellar explosion. This transient astronomical event occurs during the last stellar evolution, evolutionary stages of a massive star or when a ...

supernova
explosion that leaves a
remnant Remnant or remnants may refer to: Religion * Remnant (Bible), a recurring theme in the Bible * Remnant (Seventh-day Adventist belief), the remnant theme in the Seventh-day Adventist Church * The Remnant (newspaper), ''The Remnant'' (newspaper), a ...
. 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 In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects hav ...
; either a
white dwarf A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter Degenerate matter is a highly dense state of fermionic matter in which the Pauli exclusion principle exerts significant ...

white dwarf
,
neutron star A neutron star is the collapsed core Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this par ...
, or
black hole
black hole
.


Categories by location

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


See also

*
List of light sources This is a list of sources of light. Light sources include light bulbs and stars like the Sun. Reflectors (such as the moon, cat's eyes, and mirrors) do not actually produce the light that comes from them. Incandescence Incandescence is the emiss ...
*
List of Solar System objects The following is a list of Solar System objects by orbit, ordered by increasing distance from the Sun. Most named objects in this list have a diameter of 500 km or more. *The Sun, a spectral class G-type main-sequence star, G2V main-sequenc ...
*
List of Solar System objects by size This is a partial list of Solar System objects by size, arranged in descending order of mean volumetric radius, and divided into several size classes. These lists can also be sorted according to an object's mass and, for the largest objects, volum ...
*
Lists of astronomical objects This is a list of lists, grouped by type of astronomical object In astronomy, an astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the observable universe. In ast ...
*
Outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting ...


References


External links

*
Monthly skymaps for every location on Earth
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