Astronomy is a natural science that deals with the study of celestial objects (such as stars, planets, comets, nebulae, star clusters and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.
Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments, Nubian monuments and Stonehenge, and early civilizations such as the Babylonians, Greeks, Chinese, Indians, and Maya performed methodical observations of the night sky. 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 calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.
During the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of celestial objects, which is then analyzed 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.
Ancient astronomy is not to be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin and a part of their methods (namely, the use of ephemerides), they are distinct.
1.1 Use of terms "astronomy" and "astrophysics"
2.1 Scientific revolution
3 Observational astronomy
3.1 Radio astronomy
3.2 Infrared astronomy
3.3 Optical astronomy
3.4 Ultraviolet astronomy
3.5 X-ray astronomy
3.6 Gamma-ray astronomy
3.7 Fields not based on the electromagnetic spectrum
3.8 Astrometry and celestial mechanics
4 Theoretical astronomy
5 Specific subfields
5.1 Solar astronomy
5.2 Planetary science
5.3 Stellar astronomy
5.4 Galactic astronomy
5.5 Extragalactic astronomy
6 Interdisciplinary studies
7 Amateur astronomy
8 Major problems
9 International Year of Astronomy 2009
10 See also
13 External links
 LexicologyThe word astronomy (from the Greek words astron (ἄστρον), "star" and -nomy from nomos (νόμος), "law" or "culture") literally means "law of the stars" (or "culture of the stars" depending on the translation).
 Use of terms "astronomy" and "astrophysics"Generally, either the term "astronomy" or "astrophysics" may be used to refer to this subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties" and "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena". In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with...
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