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[[Image:Astronomybluevortex.jpg|right]]

[[Image:Astronomybluevortex.jpg|right]]

'''Astronomy'''  is the [[science|scientific study]] of [[Astronomical object|celestial objects]] (such as [[star]]s, [[planet]]s, [[comet]]s, and [[galaxy|galaxies]]) and [[Phenomenon|phenomena]] that originate outside the [[Earth's atmosphere]] (such as the [[Cosmic microwave background radiation|cosmic background radiation]]). It is concerned with the evolution, [[physics]], [[chemistry]], [[meteorology]], and [[motion (physics)|motion]] of celestial objects, as well as the [[physical cosmology|formation and development of the universe]].  

'''Astronomy'''  is the [[science|scientific study]] of [[Astronomical object|celestial objects]] (such as [[star]]s, [[planet]]s, [[comet]]s, and [[galaxy|galaxies]]) and [[Phenomenon|phenomena]] that originate outside the [[Earth's atmosphere]] (such as the [[Cosmic microwave background radiation|cosmic background radiation]]). It is concerned with the [[evolution]], [[physics]], [[chemistry]], [[meteorology]], and [[motion (physics)|motion]] of celestial objects, as well as the [[physical cosmology|formation and development of the universe]].  

Astronomy is one of the oldest sciences. Astronomers of early civilizations performed methodical observations of the night sky, and astronomical artifacts have been found from much earlier periods. However, the invention of the [[telescope]] was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as [[astrometry]], [[celestial navigation]], observational astronomy, the making of [[calendar]]s, and even [[astrology]], but professional astronomy is nowadays often considered to be synonymous with '''astrophysics'''. Since the 20th century, the field of professional astronomy split into [[observational astronomy|observational]] and [[theoretical astronomy|theoretical]] branches. Observational astronomy is focused on acquiring and analyzing data, mainly using basic principles of physics. Theoretical astronomy is oriented towards the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results, and observations being used to confirm theoretical results.

Astronomy is one of the oldest sciences. Astronomers of early civilizations performed methodical observations of the night sky, and astronomical artifacts have been found from much earlier periods. However, the invention of the [[telescope]] was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as [[astrometry]], [[celestial navigation]], observational astronomy, the making of [[calendar]]s, and even [[astrology]], but professional astronomy is nowadays often considered to be synonymous with '''astrophysics'''. Since the 20th century, the field of professional astronomy split into [[observational astronomy|observational]] and [[theoretical astronomy|theoretical]] branches. Observational astronomy is focused on acquiring and analyzing data, mainly using basic principles of physics. Theoretical astronomy is oriented towards the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results, and observations being used to confirm theoretical results.

[[Amateur astronomers]] have contributed to many important astronomical discoveries, and astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient [[phenomena]].

[[Amateur astronomers]] have contributed to many important astronomical discoveries, and astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient [[phenomena]].

Old or even ancient astronomy is not to be confused with [[astrology]], the belief system that claims that human affairs are correlated with the positions of celestial objects. Although the [[Astrology and astronomy|two fields]] share a common origin and a part of their methods (namely, the use of [[ephemeris|ephemerides]]), they are distinct. (Albrecht Unsöld, The New Cosmos: An Introduction to Astronomy and Astrophysics, SBN 3-540-67877-8  

Old or even ancient astronomy is not to be confused with [[astrology]], the belief system that claims that human affairs are correlated with the positions of celestial objects. Although the [[Astrology and astronomy|two fields]] share a common origin and a part of their methods (namely, the use of [[ephemeris|ephemerides]]), they are distinct. (Albrecht Unsöld, The New Cosmos: An Introduction to Astronomy and Astrophysics, ISBN 3-540-67877-8  

==Lexicology==

==Lexicology==

==Theoretical astronomy==

==Theoretical astronomy==

Theoretical astronomers use a wide variety of tools which include [[mathematical model|analytical models]] (for example, [[polytrope]]s to approximate the behaviors of a [[star]]) and [[computation]]al [[Numerical analysis|numerical simulations]]. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.<ref>H. Roth, ''A Slowly Contracting or Expanding Fluid Sphere and its Stability'', ''Phys. Rev.'' ('''39''', p;525–529, 1932) A.S. Eddington, ''Internal Constitution of the Stars''

Theoretical astronomers use a wide variety of tools which include [[mathematical model|analytical models]] (for example, [[polytrope]]s to approximate the behaviors of a [[star]]) and [[computation]]al [[Numerical analysis|numerical simulations]]. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.(H. Roth, ''A Slowly Contracting or Expanding Fluid Sphere and its Stability'', ''Phys. Rev.'' '''39''', p;525–529, 1932) A.S. Eddington, ''Internal Constitution of the Stars'')

Theorists in astronomy endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.

Theorists in astronomy endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.

An [[ultraviolet]] image of the Sun's active [[photosphere]] as viewed by the [[TRACE]] space telescope. ''[[NASA]] photo''.]]

An [[ultraviolet]] image of the Sun's active [[photosphere]] as viewed by the [[TRACE]] space telescope. ''[[NASA]] photo''.]]

The Sun has steadily increased in luminosity over the course of its life, increasing by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.<ref name="Environmental issues : essential primary sources.">{{cite web | last = Lerner & K. Lee Lerner | first = Brenda Wilmoth | date = 2006 | url=http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page | title = Environmental issues : essential primary sources." | publisher = Thomson Gale | accessdate = 2006-09-11 }}</ref> The [[Maunder minimum]], for example, is believed to have caused the [[Little Ice Age]] phenomenon during the [[Middle Ages]].<ref name="future-sun">{{cite web | author=Pogge, Richard W. | year=1997 | url=http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html | title=The Once & Future Sun|format=lecture notes | work=[http://www-astronomy.mps.ohio-state.edu/Vistas/ New Vistas in Astronomy] | accessdate=2005-12-07}}</ref>

The Sun has steadily increased in luminosity over the course of its life, increasing by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.<ref name="Environmental issues : essential primary sources."[http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page] The [[Maunder minimum]], for example, is believed to have caused the [[Little Ice Age]] phenomenon during the [[Middle Ages]].[http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html] [http://www-astronomy.mps.ohio-state.edu/Vistas/ New Vistas in Astronomy]

The visible outer surface of the Sun is called the [[photosphere]]. Above this layer is a thin region known as the [[chromosphere]]. This is surrounded by a transition region of rapidly increasing temperatures, then by the super-heated [[corona]].

The visible outer surface of the Sun is called the [[photosphere]]. Above this layer is a thin region known as the [[chromosphere]]. This is surrounded by a transition region of rapidly increasing temperatures, then by the super-heated [[corona]].

At the center of the Sun is the core region, a volume of sufficient temperature and pressure for [[nuclear fusion]] to occur. Above the core is the [[radiation zone]], where the plasma conveys the energy flux by means of radiation. The outer layers form a [[convection zone]] where the gas material transports energy primarily through physical displacement of the gas. It is believed that this convection zone creates the magnetic activity that generates sun spots.<ref name="solar FAQ" />

At the center of the Sun is the core region, a volume of sufficient temperature and pressure for [[nuclear fusion]] to occur. Above the core is the [[radiation zone]], where the plasma conveys the energy flux by means of radiation. The outer layers form a [[convection zone]] where the gas material transports energy primarily through physical displacement of the gas. It is believed that this convection zone creates the magnetic activity that generates sun spots.

A solar wind of plasma particles constantly streams outward from the Sun until it reaches the [[heliopause]]. This solar wind interacts with the [[magnetosphere]] of the Earth to create the [[Van Allen radiation belt]]s, as well as the [[aurora (astronomy)|aurora]] where the lines of the [[Earth's magnetic field]] descend into the [[Earth's atmosphere|atmosphere]].<ref>{{cite web | author = D. P. Stern, M. Peredo | date = 2004-09-28 | url=http://www-istp.gsfc.nasa.gov/Education/Intro.html | title = The Exploration of the Earth's Magnetosphere | publisher = NASA | accessdate = 2006-08-22 }}</ref>

A solar wind of plasma particles constantly streams outward from the Sun until it reaches the [[heliopause]]. This solar wind interacts with the [[magnetosphere]] of the Earth to create the [[Van Allen radiation belt]]s, as well as the [[aurora (astronomy)|aurora]] where the lines of the [[Earth's magnetic field]] descend into the [[Earth's atmosphere|atmosphere]].[http://www-istp.gsfc.nasa.gov/Education/Intro.html]

===Planetary science===

===Planetary science===

This astronomical field examines the assemblage of [[planet]]s, [[natural satellite|moons]], [[dwarf planet]]s, [[comet]]s, [[asteroid]]s, and other bodies orbiting the Sun, as well as extrasolar planets. The [[solar system]] has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of this planetary system, although many new discoveries are still being made.<ref name="geology">{{cite book | author=J. F. Bell III, B. A. Campbell, M. S. Robinson | title=Remote Sensing for the Earth Sciences: Manual of Remote Sensing | publisher=John Wiley & Sons | edition = 3rd | year=2004 | url=http://marswatch.tn.cornell.edu/rsm.html | accessdate = 2006-08-23 }}</ref>

This astronomical field examines the assemblage of [[planet]]s, [[natural satellite|moons]], [[dwarf planet]]s, [[comet]]s, [[asteroid]]s, and other bodies orbiting the Sun, as well as extrasolar planets. The [[solar system]] has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of this planetary system, although many new discoveries are still being made.(Remote Sensing for the Earth Sciences: Manual of Remote Sensing [http://marswatch.tn.cornell.edu/rsm.html}

The black spot at the top is a [[dust devil]] climbing a crater wall on [[Mars (planet)|Mars]]. This moving, swirling column of [[Atmosphere of Mars|Martian atmosphere]] (comparable to a terrestrial [[tornado]]) created the long, dark streak. ''[[NASA]] image''.]]

The black spot at the top is a [[dust devil]] climbing a crater wall on [[Mars (planet)|Mars]]. This moving, swirling column of [[Atmosphere of Mars|Martian atmosphere]] (comparable to a terrestrial [[tornado]]) created the long, dark streak. ''[[NASA]] image''.]]