Astronomy

Astronomy, is the science that deals with the origin, evolution, composition, distance, and motion of all bodies and scattered matter in the universe. It includes astrophysics, which discusses the physical properties and structure of all cosmic matter.

Astronomy is the most ancient of the sciences, having existed since the dawn of recorded civilization. Much of the earliest knowledge of the celestial bodies is often credited to the Babylonians. They are thought to have recognized a number of prominent constellations as early as 3000 BC and to have developed a calendar based on the regularity of certain astronomical events some centuries thereafter.

The ancient Greeks introduced various influential cosmological ideas. During the 6th century BC Pythagoras proposed the notion of a spherical Earth and a universe populated by objects whose motions were governed by the harmonious relations of natural laws. Later Greek philosophers taught that the sky was a hollow globe surrounding the Earth and having the stars inlaid like jewels on its inner surface.

The sky was supported on an axis thrust through the Earth; on this axis the sky rotated westward daily, causing the celestial bodies to rise and set. During the 2nd century AD Ptolemy (Claudius Ptolemaus), one of the most celebrated of the ancient Greek astronomers, put forth a conception of an Earth-centred (geocentric) universe that influenced astronomical thought for more than 1,300 years.

In the Ptolemaic system, each planet moved in a small circle, the epicycle, in the period of its actual revolution around the heavens relative to the Sun's position. Meanwhile, the centre of this circle moved eastward around the Earth on a larger circle in the observed period of the planet's revolution relative to the stars.

During the 16th century the Polish astronomer Nicolaus Copernicus disposed of much of the complexity of the Ptolemaic system by assigning the central position to the Sun. In this revolutionary system the Earth, attended by the Moon, became one of the planets revolving around the Sun. Copernicus also proposed the daily axial rotation of the Earth from west to east, so that the daily circling of the heavenly bodies around the Earth results simply from its apparent motion.

Published in De revolutionibus orbium coelestium libri VI ("Six Books Concerning the Revolutions of the Heavenly Orbs") in 1543, the Copernican heliocentric theory ushered in the age of modern astronomy.

The 17th century witnessed several momentous developments that led to major advances in astronomy.

These were the discovery of the principles of planetary motion by Johannes Kepler, the application of the telescope to astronomical observation by Galileo Galilei, and the formulation of the laws of motion and gravitation by Isaac Newton.

Other significant contributions followed in rapid succession.

In 1750 Thomas Wright, for example, postulated that the universe was made up of numerous galaxies. Later in the century another English astronomer, William Herschel, undertook the first thorough telescopic survey of the heavens and established the foundations of modern stellar astronomy.

Spectroscopy and photography were adopted for astronomical research in the 19th century. They enabled investigators to measure the quantity and quality of light emitted by stars and nebulae (clouds of interstellar gas and dust), making it possible for them to conduct studies of the brightness, temperature, and chemical composition of such cosmic objects. It was soon recognized that the properties of all celestial bodies, including the planets of the solar system, could only be understood in terms of the physics of their atmosphere and interior.

The trend toward the application of physical laws to the interpretation of observational data gained impetus during the early 1920s, and many astronomers began referring to themselves as astrophysicists. This tendency continues to prevail.

The major areas of current interest--X-ray astronomy, gamma-ray astronomy, infrared astronomy, and radio astronomy--are all basically concerned with physics and engineering, the knowledge of the latter having utmost importance in the construction of observational instruments and auxiliary equipment.

Technological advances such as electronic radar and radio units, high-speed computers, electronic radiation detectors, and Earth-orbiting observatories and long-range planetary probes have greatly broadened the scope of both theoretical and observational research on astronomical phenomena.

- Encyclopedia Britannica

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'Astronomy' literally means, "law of the stars" and refers to the science involving the observation and explanation of events occurring beyond the Earth and its atmosphere. It studies the origins, evolution, and physical and chemical properties of objects that may be observed in the sky (and are beyond the atmosphere), as well as the connected processes and phenomena.

Astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and monitoring of transient phenomena. Astronomy is not to be confused with astrology, which assumes that people's destiny and human affairs in general are correlated to the apparent positions of astronomical objects in the sky - although the two fields share a common origin, they are quite different; astronomers embrace the scientific method, while astrologers do not.

Divisions of astronomy

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 paved the way for 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 concerns itself much more with trying to observe and understand the actual physical nature of celestial objects - what makes them "tick".

Ever since the twentieth century the field of professional astronomy has tended to 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 figuring out 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.