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'''Astronomical objects''' are significant [[entity|physical entities]], associations or structures which current [[science]] has confirmed to exist in [[space]]. This does not necessarily mean that more current science will not disprove their existence. Some astronomical objects, such as [[Themis (moon)|Themis]] and [[Neith (moon)|Neith]] are, in light of more recent findings, considered not to exist at all. Others, like [[Pluto]] and [[Ceres (asteroid)|Ceres]], prove to be of an entirely different nature than first expected. In these cases, the [[scientific community]] must come to a consensus as to the new status of these objects. Obviously, not all scientists will agree; this gives birth to [[fringe science]]. However, fringe science is not always [[bad science]]. Some of our most fundamental [[scientific theories]], such as the [[superstring theory]] and [[plate tectonics]], were once considered fringe. Even in the [[mainstream]] community, new ideas are constantly changing the way we view the universe at large. Astronomical objects thought to exist based on scientific evidence are considered [[List of hypothetical astronomical objects|hypothetical]].

'''Astronomical objects''' or ''celestial objects'' are naturally occurring [[physical]] [[entities]], associations or structures 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.

Astronomical objects can be easily confused with "'''astronomical bodies'''". The term "body" indicates a simple object, such as a [[planet]]. These terms differ from "'''celestial objects'''" and "'''celestial bodies'''" only in that the latter terms do not include the [[Earth]]. The table below lists the general categories of objects by their location or structure.[http://en.wikipedia.org/wiki/Celestial_objects]

[[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 [http://en.wikipedia.org/wiki/Dwarf_galaxy dwarf galaxies]. The galaxies are organized into groups and clusters, often within larger [http://en.wikipedia.org/wiki/Superclusters 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 [http://en.wikipedia.org/wiki/Supermassive_black_hole supermassive black hole], which may result in an active galactic nucleus. Galaxies can also have [[satellites]] in the form of dwarf galaxies and [http://en.wikipedia.org/wiki/Globular_cluster 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 [http://en.wikipedia.org/wiki/Protoplanetary_disk protoplanetary disks] that surrounds newly created stars.

 

The various distinctive types of [[stars]] are shown by the [http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram 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 [http://en.wikipedia.org/wiki/Variable_star variable star]. An example of this is the instability strip, a region of the H-R diagram that includes [http://en.wikipedia.org/wiki/Delta_Scuti_variable Delta Scuti], [http://en.wikipedia.org/wiki/RR_Lyrae_variable RR Lyrae] and [http://en.wikipedia.org/wiki/Cepheid_variable 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 [http://en.wikipedia.org/wiki/Compact_star compact object]; either a [http://en.wikipedia.org/wiki/White_dwarf white dwarf], [http://en.wikipedia.org/wiki/Neutron_star neutron star], or [[black hole]].

[[Category: Astronomy]]

[[Category: Astronomy]]