Astronomical object

Source: Wikipedia, the free encyclopedia.
This article is about naturally occurring objects. For astronomical objects of the Solar System, see List of Solar System objects. For artificial objects, see Satellite. "Celestial object" and "Celestial body" redirect here. For the subtle body postulated in philosophy, see Body of light. For other uses, see Celestial.
Selection of astronomical bodies and objects

An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within 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

coma and tail
.

History

Further information:
History of Astronomy
See also: Scientific Revolution and Copernican Revolution

Astronomical objects such as

universities
to teach people more about astronomy.

During the

Sir William Herschel discovered the new planet Uranus
, being the first discovered planet not visible by the naked eye.

In the 19th and 20th century, new technologies and scientific innovations allowed scientists to greatly expand their understanding of astronomy and astronomical objects. Larger telescopes and observatories began to be built and scientists began to print images of the Moon and other celestial bodies on photographic plates. New

Hertzsprung-Russell diagram was developed by astronomers Ejnar Hertzsprung and Henry Norris Russell independently of each other, which plotted stars based on their luminosity and color and allowed astronomers to easily examine stars. It was found that stars commonly fell on a band of stars called the main-sequence stars on the diagram. A refined scheme for stellar classification was published in 1943 by William Wilson Morgan and Philip Childs Keenan based on the Hertzsprung-Russel Diagram. Astronomers also began debating whether other galaxies existed beyond the Milky Way, these debates ended when Edwin Hubble identified the Andromeda nebula
as a different galaxy, along with many others far from the Milky Way.

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]

Galaxies have 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 surround newly formed stars.

The various distinctive types of stars are shown by the

compact object; either a white dwarf, neutron star, or black hole
.

Shape

Further information: Spherical Earth § Cause
See also: Equatorial bulge and Hydrostatic equilibrium § Planetary geology
Composite image showing the round dwarf planet Ceres; the slightly smaller, mostly round Vesta; and the much smaller, much lumpier Eros

The

spheroidal shape can be seen on smaller rocky planets like Mars to gas giants like Jupiter
.

Any natural Sun-orbiting body that has not reached hydrostatic equilibrium is classified by the IAU as a small Solar System body (SSSB). These come in many non-spherical shapes which are lumpy masses accreted haphazardly by in-falling dust and rock; not enough mass falls in to generate the heat needed to complete the rounding. Some SSSBs are just collections of relatively small rocks that are weakly held next to each other by gravity but are not actually fused into a single big bedrock. Some larger SSSBs are nearly round but have not reached hydrostatic equilibrium. The small Solar System body 4 Vesta is large enough to have undergone at least partial planetary differentiation.

Stars like the Sun are also spheroidal due to gravity's effects on their

stellar fusion
is a much greater source of heat for stars compared to the initial heat released during their formation.

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.

Solar bodies Extrasolar Observable universe
Simple bodies Compound objects Extended objects
Planets
Dwarf planets
Minor planets
Stars (see sections below)
By luminosity / evolution
Compact stars
By
peculiar stars
By
spectral types
  • O (blue)
  • B (blue-white)
  • A (white)
  • F (yellow-white)
  • G (yellow)
  • K (orange)
  • M (red)
Systems
Stellar groupings
Galaxies
Discs and media
Cosmic scale
Logarithmic representation of the observable
universe with the notable astronomical objects
known today. From down to up the celestial
bodies are arranged according to their proximity
to the Earth.
Infographic listing 210 notable astronomical
objects marked on a central logarithmic map of
the observable universe. A small view and some
distinguishing features for each astronomical
object are included.

See also

References

  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.{{cite web}}: CS1 maint: numeric names: authors list (link)
  2. ISBN 81-7371-043-0
    .
  3. ISBN 0-19-512664-5
    .
  4. ISBN 978-0-521-82048-6
    .
  5. ISBN 0521318874
    . Retrieved 13 February 2017.
  6. doi:10.1017/S1743921309990809
    .
  7. ISBN 0-387-20089-4
    .

External links

Wikimedia Commons has media related to Astronomical objects.
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