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Astronomy

Astronomy is one of the few sciences where amateurs still play an active role, especially in the discovery and monitoring of transient phenomena. Astronomy is not to be confused with astrology, a pseudoscience that attempts to predict a person's destiny by tracking the paths of astronomical objects. Although the two fields share a common origin, they are quite different; astronomers embrace the scientific method, while astrologers do not.

Table of contents

1 Divisions of astronomy 1.1 By subject or problem addressed 1.2 Ways of obtaining information 2 Short history 3 Timelines in astronomy 4 See also 5 Astronomy tools 6 External links 6.3 Organizations 6.4 References: Formulas and Constants 6.5 External links

Divisions of astronomy

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 getting data, which involves building and maintaining instruments and processing the resulting data; 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 are also categorized in another two ways: by "subject", usually according to the region of space (e.g. Galactic astronomy) or "problems addressed" (such as star formation or cosmology); or by the way used for obtaining information.

By subject or problem addressed

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• Astrobiology: the study of the advent and evolution of biological systems in the universe.
• 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.
• Cosmology: the study of the universe as a whole and its 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.
• Galaxy formation and evolution: the study of the formation of the galaxies, and their evolution.
• Planetary Sciences: the study of the planets of the solar system.
• 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.

• Archaeoastronomy
• Astrochemistry
• Planetary sciences
• Cosmology

Ways of obtaining information

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

• Optical astronomy describes the techniques used to detect and analyze light in and slightly around the wavelengths that can be detected with the eyes (about 400 - 800 nm). The most common tool is the telescope, with electronic imagers and spectrographs.
• Infrared astronomy deals with the detection of infrared radiation (wavelengths longer than red light). The most common tool is the telescope but with the instrument optimized for infrared. Space telescopes are also used to eliminate noise (electromagnetic interference) from the atmosphere.
• Radio astronomy uses completely different instruments to detect radiation of wavelengths of mm to cm. The receivers are similar to those used in radio broadcast transmission (which uses those wavelengths of radiation). See also Radio telescopes.
• High-energy astronomy

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

The atmosphere is opaque at the wavelengths used by X-ray astronomy, gamma-ray astronomy, UV astronomy and, except for a few wavelength "windows", Far infrared astronomy, so observations can be carried out only from balloons or space observatories.

Short history

Astronomy was mostly stagnant in medieval Europe, but flourished meanwhile in the Arab world. The late 9th century Islamic astronomer al-Farghani (Abu'l-Abbas Ahmad ibn Muhammad ibn Kathir 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, Iran, by the astronomer al-Khujandi who observed a series of meridian transits of the Sun, which allowed him to calculate the obliquity of the ecliptic. In Persia, Omar Khayyam (Ghiyath al-Din Abu'l-Fath Umar ibn Ibrahim al-Nisaburi al-Khayyami) compiled many tables and performed a reformation of the calendar that was more accurate than the Julian and came close to the Gregorian.

During the Renaissance Copernicus proposed a heliocentric model of the Solar System. His work was defended, expanded upon, and corrected by Galileo Galilei and Johannes Kepler. 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. It was left to Newton's invention of celestial dynamics and his law of gravitation to finally explain the motions of the planets.

Stars were found to be faraway objects. With the advent of spectroscopy it was proved that they were similar to our own sun, but with a wide range of temperatures, masses and sizes. The existence of our 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. 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.

For a more detailed history of astronomy, see the history of astronomy.

. The ejection of gas, from the dying star at the center, has symmetrical patterns unlike the chaotic patterns expected from an ordinary explosion.]]

Timelines in astronomy

• Timeline of black hole physics
• Timeline of cosmology
• Timeline of cosmic microwave background astronomy
• Timeline of other background radiation fields
• Timeline of galaxies, clusters of galaxies, and large scale structure
• Timeline of the interstellar medium and intergalactic medium
• Timeline of white dwarfs, neutron stars, and supernovae
• Timeline of stellar astronomy
• Timeline of solar astronomy
• Timeline of solar system astronomy
• Timeline of astronomical maps, catalogs, and surveys
• Timeline of telescopes, observatories, and observing technology
• Timeline of artificial satellites and space probes

• List of astronomical topics
• Astronomers and Astrophysicists
• Space science
• Astronomical naming conventions
• Astronomical symbols
• Astronomical cycles
• International Astronomical Union
• American Astronomical Society
• Royal Astronomical Society
• European Southern Observatory

• Telescope
• Computers
• Calculator
• Observatory
• Space observatory

• American Association of Variable Star Observers
• American Astronomical Society
• Astronomical Society of the Pacific
• Cassini Imaging Laboratory - Stunning images of the planets taken by the Cassini exploratory spacecraft
• Czech Astronomical Society
• Durham Region Astronomical Association
• Hawaiian Astronomical Society
• Herzberg Institute of Astrophysics
• National Optical Astronomy Observatories
• North York Astronomical Association
• Open Encyclopedia Project - Astronomy Section.
• Royal Astronomical Society of Canada
• Royal Astronomical Society (UK)
• Royal Astronomical Society of New Zealand
• Saint Louis Astronomical Society
• Society for Popular Astronomy (UK)

• Astronomy Formulas
• Astronomical Constants Index
• Zombeck's Handbook of Space Astronomy and Astrophysics

• Astronomy sites for educators
• Los Alamos Astrophysics e-Print Database
• Astronomy Picture of the Day
• Bruce Medalists (annual astronomical award since 1898)
• Islamic and Arab Astronomy

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