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AstronomyFrom Wikipedia, the free encyclopedia.
Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally, "law of the stars") is the science of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth's atmosphere (such as auroras and cosmic background radiation). It is concerned with the formation and development of the universe, the evolution, physics, and chemistry of celestial objects, and the calculation of the motion of such objects (see astrometry). Astronomical observations are relevant not only for astronomy as such, but also as tests of fundamental theories in physics, such as general relativity. Theoretical astrophysics is complementary to observational astronomy in that it seeks to explain astronomical phenomena. Astronomy is one of the oldest sciences. Astronomers of ancient Greece practiced a scientific methodology, and advanced observation techniques may have been known much earlier (see archaeoastronomy). Historically, 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. Modern astronomy is not to be confused with astrology, the belief system that claims human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are fundamentally different: astronomers employ the scientific method, while astrologers do not.
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Divisions
In Babylon, and ancient Greece, astronomy consisted largely of astrometry, measuring positions of stars and planets in the sky. Later, with the work of astronomers Kepler and Newton, whose work led to the development of celestial mechanics, the mathematical prediction of the motions of celestial bodies interacting gravitationally became the focus of astronomy. This was applied to solar system objects in particular. 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. Since the twentieth century, the field of professional astronomy has split into observational astronomy and theoretical astrophysics. Observational astronomy is concerned mostly with acquiring data, which involves building and maintaining instruments and processing the results; 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. 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. [edit]
By subject or problem addressed
Other disciplines that may be considered part of astronomy: See the list of astronomical topics for a more exhaustive list of astronomy related pages. [edit]
By methods of data collection
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. Neutrino detectors have been used to observe solar neutrinos, and neutrino emissions from supernovae have also been detected. A traditional division of astronomy is given by the region of the electromagnetic spectrum observed:
Optical and radio astronomy can be performed with ground-based observatories, because the Earth's atmosphere is transparent at the wavelengths being detected. Infrared radiation is heavily absorbed by atmospheric water vapor, so infrared observatories have to be located in high, dry places or in space. 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 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. Planetary astronomy has benefited from direct observation in the form of spacecraft and sample return missions. These include fly-by missions with remote sensors, landing vehicles that can perform experiments on the surface materials, impactors that allow remote sensing of buried materials, and sample return missions that allow direct laboratory examination. [edit]
History
In early times, astronomy only comprised the observation and predictions of the motions of the naked-eye objects. Aristotle said that the Earth was the center of the Universe and everything rotated around it in orbits that were perfect circles. Aristotle had to be right because people thought that Earth had to be in the center with everything rotating around it because the wind would not scatter leaves, and birds would only fly in one direction. For a long time, people thought that Aristotle was right, but it is probable that Aristotle accidentally did more to hinder our knowledge than help it. The first ancestor of an astronomy computer, was the Antikythera mechanism, an ancient Greek device for calculating the movements of planets, dating from about 80 BC. It was discovered in an ancient shipwreck off the Greek island of Antikythera, between Kythera and Crete. The device became famous for its use of a differential gear, previously believed to have been invented in the 16th century and the miniaturization and complexity of its parts, comparable to a clock made in the 18th century. The original mechanism is displayed in the Bronze collection of the National Archaeological Museum of Athens, accompanied by a replica. Another replica is on display at the American Computer Museum in Bozeman, Montana. The Hindu vedic text, Rigveda refers to the 27 constellations associated with the motions of the sun and also the 12 zodiacal divisions of the sky. The ancient Greeks made important contributions to astronomy, among them the definition of the magnitude system. The Bible contains a number of statements on the position of the earth in the universe and the nature of the stars and planets, most of which are poetic rather than literal; see Biblical cosmology. In 500 AD, Aryabhata presented a mathematical system that described the earth as spinning on its axis and considered the motions of the planets with respect to the sun. East Asia's first astronomical observatory was developed in Silla, one of Three Kingdoms of Korea, under the reign of Queen Seondeok of Silla. It was termed Cheomsongdae, and is one of the oldest surviving scientific installations on Earth. It means star-gazing tower in Korean. Although classical astronomy was one of the seven key subjects taught at medieval universities in Europe, observational astronomy was mostly stagnant in medieval Europe until XIII century, when lived astronomers and astrologers as Johannes de Sacrobosco, in England, and Guido Bonatti from Forlì, in Italy. Tycho Brahe's work is very famous, in the 16th Century. However, observational astronomy flourished in the Iranian world and other parts of Islamic realm. The late 9th century Persian astronomer al-Farghani wrote extensively on the motion of celestial bodies. His work was translated into Latin in the 12th century. In the late 10th century, a huge observatory was built near Tehran, Persia (now Iran), by the Persian astronomer al-Khujandi, who observed a series of meridian transits of the Sun, which allowed him to calculate the obliquity of the ecliptic. Also in Persia, Omar Khayyám performed a reformation of the calendar that was more accurate than the Julian and came close to the Gregorian. Abraham Zacuto was responsible in the 15th century for the adaptations of astronomical theory for the practical needs of Portuguese caravel expeditions. 
During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the Solar System. His work was defended, expanded upon, and corrected by Galileo Galilei and Johannes Kepler. Galileo added the innovation of using telescopes to enhance his observations. Kepler was the first to devise a system that described correctly the details of the motion of the planets with the Sun at the center. However, Kepler did not succeed in formulating a theory behind the laws he wrote down, and parts of his discoveries are no longer considered significant, e.g., the spacing of planetary orbits to allow insertion of regular solids between adjacent planets' spheres. It was left to Newton's invention of celestial dynamics and his law of gravitation to finally explain the motions of the planets. Newton also developed the reflecting telescope. Stars were found to be faraway objects. With the advent of spectroscopy it was proved that they were similar to Earth's own sun, but with a wide range of temperatures, masses, and sizes. The existence of Earth's galaxy, the Milky Way, as a separate group of stars was only proven in the 20th century, along with the existence of "external" galaxies, and soon after, the expansion of the universe, seen in the recession of most galaxies from us. Modern astronomy has also discovered many exotic objects such as quasars, pulsars, blazars and radio galaxies, and has used these observations to develop physical theories which describe some of these objects in terms of equally exotic objects such as black holes and neutron stars. Physical cosmology made huge advances during the 20th century, with the model of the Big Bang heavily supported by the evidence provided by astronomy and physics, such as the cosmic microwave background radiation, Hubble's law, and cosmological abundances of elements. [edit]
Astronomical timelines
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Astronomy tools[edit]
External links
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