Astronomy

:This article is about the science branch. For information about the magazine, see Astronomy (magazine).

Divisions

In ancient Greece and other early civilizations, astronomy consisted largely of astrometry, measuring positions of stars and planets in the sky. Later, the work of Kepler and Newton, whose work led to the development of celestial mechanics, mathematically predicting the motions of celestial bodies interacting under gravity, and solar system objects in particular. Much of the effort in these two areas, once done largely by hand, is highly automated nowadays, to the extent that they are rarely considered as independent disciplines anymore. Motions and positions of objects are now more easily determined, and modern astronomy is more concerned with observing and understanding the actual physical nature of celestial objects.

Related Topics:
Ancient Greece - Astrometry - Kepler - Newton - Celestial mechanics - Solar system

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Since the twentieth century, the field of professional astronomy has split into observational astronomy and theoretical astrophysics. Although most astronomers incorporate elements of both into their research, because of the different skills involved, most professional astronomers tend to specialize in one or the other. Observational astronomy is concerned mostly with acquiring data, which involves building and maintaining instruments and processing the resulting information; this branch is at times referred to as "astrometry" or simply as "astronomy". Theoretical astrophysics is concerned mainly with ascertaining the observational implications of different models, and involves working with computer or analytic models.

Related Topics:
Observational astronomy - Theoretical astrophysics

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The fields of study can also be categorized in other ways. Categorization by the region of space under study (for example, Galactic astronomy, Planetary Sciences); by subject, such as star formation or cosmology; or by the method used for obtaining information.

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By subject or problem addressed

• Astrometry: the study of the position of objects in the sky and their changes of position. Defines the system of coordinates used and the kinematics of objects in our galaxy.
• Astrophysics: the study of physics of the universe, including the physical properties (luminosity, density, temperature, chemical composition) of astronomical objects.
• Cosmology: the study of the origin of the universe and its evolution. The study of cosmology is theoretical astrophysics at its largest scale.
• Galaxy formation and evolution: the study of the formation of the galaxies, and their evolution.
• Galactic astronomy: the study of the structure and components of our galaxy and of other galaxies.
• Extragalactic astronomy: the study of objects (mainly galaxies) outside our galaxy.
• Stellar astronomy: the study of the stars.
• Stellar evolution: the study of the evolution of stars from their formation to their end as a stellar remnant.
• Star formation: the study of the condition and processes that led to the formation of stars in the interior of gas clouds, and the process of formation itself.
• Planetary Sciences: the study of the planets of the Solar System.
• Astrobiology: the study of the advent and evolution of biological systems in the Universe.

Other disciplines that may be considered part of astronomy:

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• Archaeoastronomy
• Astrochemistry
• Astrosociobiology
• Astrophilosophy

See the list of astronomical topics for a more exhaustive list of astronomy-related pages.

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Ways of obtaining information

:Main article: Observational astronomy.

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In astronomy, information is mainly received from the detection and analysis of light and other forms of electromagnetic radiation. Other cosmic rays are also observed, and several experiments are designed to detect gravitational waves in the near future.

Related Topics:
Information - Electromagnetic radiation - Cosmic ray - Gravitational waves

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A traditional division of astronomy is given by the region of the electromagnetic spectrum observed:

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• Optical astronomy is the part of astronomy that uses optical components (mirrors, lenses, CCD detectors and photographic films) to observe light from near infrared to near ultraviolet wavelengths. Visible light astronomy (using wavelengths that can be detected with the eyes, about 400 - 700 nm) falls in the middle of this range. The most common tool is the telescope, with electronic imagers and spectrographs.
• Infrared astronomy deals with the detection and analysis of infrared radiation (wavelengths longer than red light). The most common tool is the telescope but using a detector which is sensitive to the infrared. Space telescopes are also used to eliminate noise (electromagnetic interference) from the atmosphere.
• Radio astronomy detects radiation of millimetre to dekametre wavelength. The receivers are similar to those used in radio broadcast transmission but much more sensitive. See also Radio telescopes.
• High-energy astronomy includes X-ray astronomy, gamma-ray astronomy, and extreme UV (ultraviolet) astronomy, as well as studies of neutrinos and cosmic rays.

Optical and radio astronomy can be performed with ground-based observatories, because the atmosphere is transparent at the wavelengths being detected. Infrared light is heavily absorbed by water vapor, so infrared observatories have to be located in high, dry places or in space.

Related Topics:
Observatories - Atmosphere - Water vapor

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The atmosphere is opaque at the wavelengths of X-ray astronomy, gamma-ray astronomy, UV astronomy and (except for a few wavelength "windows") Far infrared astronomy, so observations

Related Topics:
Opaque - X-ray astronomy - Gamma-ray astronomy - UV astronomy - Far infrared astronomy

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must be carried out mostly from balloons or space observatories. Powerful gamma rays can, however be detected by the large air showers they produce, and the study of cosmic rays can also be regarded as a branch of astronomy.

Related Topics:
Balloon - Space observatories - Gamma ray - Air shower - Cosmic ray

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