International Astronomical Union

The International Astronomical Union (IAU) unites national astronomical societies from around the world. It is a member of the International Council of Science (ICSU). It is the most popularly recognised authority for the naming of stars, planets, asteroids and other celestial bodies and phenomena in the scientific community.

Working groups include the Working Group for Planetary System Nomenclature (WGPSN), which maintains the astronomical naming conventions and planetary nomenclature for planetary bodies. The IAU is also responsible for the system of Astronomical Telegrams, although it does not run it. The Minor Planet Center (MPC), a clearinghouse for all non-planetary or non-moon bodies in the solar system, also operates under the IAU.

The IAU was founded in 1919, as a merger of various international projects including the Carte du Ciel, the Solar Union and the International Time Bureau (Bureau International de l'Heure). The first president was Benjamin Baillaud.

The IAU currently has 9040 individual members, i.e., professional astronomers (mainly) at the PhD level; and 63 national members, i.e., countries that are affiliated with the IAU. 87 percent of all members are male; 13 percent are female. The current president is Ronald D. Ekers.

The XXVIth General Assembly of the International Astronomical Union (August 2006) will be held in Prague, Czech Republic.

Stellar Astronomy - A Time Line

Timeline of stellar astronomy

* 134 BC - Hipparchus creates the magnitude scale of stellar apparent luminosities
* 1596 - David Fabricius notices that Mira's brightness varies
* 1672 - Geminiano Montanari notices that Algol's brightness varies
* 1686 - Gottfried Kirch notices that Chi Cygni's brightness varies
* 1718 - Edmund Halley discovers stellar proper motions by comparing his astrometric measurements with those of the Greeks
* 1782 - John Goodricke notices that the brightness variations of Algol are periodic and proposes that it is partially eclipsed by a body moving around it
* 1784 - Edward Piggot discovers the first Cepheid variable star
* 1838 - Thomas Henderson, Friedrich Struve, and Friedrich Bessel measure stellar parallaxes
* 1844 - Friedrich Bessel explains the wobbling motions of Sirius and Procyon by suggesting that these stars have dark companions

* 1906 - Arthur Eddington begins his statistical study of stellar motions
* 1908 - Henrietta Leavitt discovers the Cepheid period-luminosity relation
* 1910 - Ejnar Hertzsprung and Henry Norris Russell study the relation between magnitudes and spectral types of stars
* 1924 - Arthur Eddington develops the main sequence mass-luminosity relationship
* 1929 - George Gamow proposes hydrogen fusion as the energy source for stars
* 1938 - Hans Bethe and Carl von Weizsacker detail the proton-proton chain and CNO cycle in stars
* 1939 - Rupert Wildt realizes the importance of the negative hydrogen ion for stellar opacity
* 1952 - Walter Baade distinguishes between Cepheid I and Cepheid II variable stars
* 1953 - Fred Hoyle predicts a carbon-12 resonance to allow stellar triple alpha reactions at reasonable stellar interior temperatures
* 1961 - Chushiro Hayashi publishes his work on the Hayashi track of fully convective stars
* 1963 - Fred Hoyle and William Fowler conceive the idea of supermassive stars
* 1964 - Subrahmanyan Chandrasekhar and Richard Feynman develop a general relativistic theory of stellar pulsations and show that supermassive stars are subject to a general relativistic instability
* 1967 - Eric Becklin and Gerry Neugebauer discover the Becklin-Neugebauer object at 10 micrometres

History of astronomy

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 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.

Observational astronomy was mostly stagnant in medieval Europe, but 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, 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. 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 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. 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.

Ways of obtaining information

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.

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

* 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.

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.

Sub Divisions of Astronomy

* 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:

* Archaeoastronomy
* Astrochemistry
* Astrosociobiology
* Astrophilosophy

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

Samuel Oschin telescope

The Samuel Oschin telescope is a 48-inch (1.22m) Schmidt camera at the Palomar Observatory in northern San Diego County, California. The instrument is strictly a camera; there is no provision for an eyepiece to look through it. It originally used large glass photographic plates. Since the focal plane is curved these plates had to be preformed in a special jig before being loaded into the camera. The camera has been converted to use a CCD imager. This is a mosaic of 112 CCDs covering the whole (4 degree by 4 degree) field of view of the camera, the largest CCD mosaic used in an astronomical camera at this time.

Schmidt camera

A Schmidt camera is an astronomical camera designed to provide wide fields of view with limited aberrations. Other similar designs are the Wright Camera and Lurie-Houghton telescope.

Invention and Design

The Schmidt camera was designed by Bernhard Schmidt (1879-1935). Its optical components are an easy to make spherical primary mirror, and an aspherical correcting lens, known as a corrector plate, located at the radius of curvature of the primary mirror. The film or other detector is placed inside the camera, at the prime focus. The design is noted for allowing very fast focal ratios, while controlling coma and astigmatism.

Schmidt cameras have very strongly curved focal planes, thus requiring that the film, plate, or other detector be correspondingly curved. In some cases the detector is made curved; in others flat media is mechanically conformed to the shape of the focal plane through the use of retaining clips or bolts, or by the application of a vacuum.

Applications

The Schmidt camera is typically used as a survey instrument, for research programs in which a large amount of sky must be covered. These include astronomical surveys, comet and asteroid searches, and nova patrols.

In addition, Schmidt cameras and derivative designs are frequently used for tracking artificial earth satellites.

Starting in the early 1970s, Celestron marketed an 8-inch Schmidt Camera. The camera was focused in the factory and was made of materials with low expansion coefficients so it would never need to be focused in the field. Early models required the photographer to cut and develop individual frames of 35mm film as the film holder could only hold one frame of film. About 300 Celestron Schmidt Cameras were produced.

The Schmidt system was popular, used in reverse, for television projection systems. Large Schmidt projectors were used used in theaters but systems as small as 8-inches were made for home use and other small venues.

Arguably the most famous and productive Schmidt camera is the Oschin Schmidt Telescope at Palomar Observatory. It was used for the National Geographic Society - Palomar Observatory Sky Survey (POSS), the POSS-II survey, the Palomar-Leiden (asteroid) Surveys, and other projects. The telescope used in the Lowell Observatory Near-Earth-Object Search (LONEOS) is also a Schmidt camera.

Derivative Designs

Prior to Schmidt's design the solution to spherical aberration was to place an aperture stop at the center of curvature of the mirror, stopping the aperture to f/10. This removes spherical aberration while preserving the wide field of the short focal-length mirror. However, it is at the cost of light-gathering ability. Although this solution was well-known long before Bernhard Schmidt invented his corrector plate the design is known as a "lensless Schmidt".

In 1940, James Baker of Harvard University modified the Schmidt camera design to include a convex secondary mirror, which reflected light back toward the primary. The photographic plate was then installed near the primary, facing the sky. This variant is called the Baker-Schmidt camera.

The Baker-Nunn design, by Dr. Baker and Joseph Nunn, replaces the Baker-Schmidt camera's corrector plate with a small triplet corrector lens closer to the focus of the camera.

The Mersenne-Schmidt camera consists of a concave paraboloidal primary mirror, a convex spherical secondary mirror, and a concave spherical tertiary mirror.

The addition of a flat secondary mirror at 45° to the optical axis of a Schmidt camera creates a Schmidt-Newtonian telescope. This design is popular amongst amateur astronomers.

The addition of a convex secondary mirror directing light through a hole in the primary mirror creates a Schmidt-Cassegrain telescope.

Comet Shoemaker-Levy 9

Comet Shoemaker-Levy 9 (formally designated D/1993 F2) was discovered in a photograph taken on the night of March 24, 1993 with the 0.4-metre Schmidt telescope at the Mount Palomar Observatory in California, and was the ninth comet discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy. It turned out to be the first comet observed orbiting a planet (Jupiter, in this case) and not the Sun [1]. The comet was also unusual because it was in fragments (ranging in size up to 2 kilometres in diameter), due to a close encounter with Jupiter in July 1992 when it approached closer to the planet than its Roche limit and was pulled apart by tidal forces.

Between July 16 and July 22, 1994, the fragments of the comet collided with Jupiter's southern hemisphere at 60 kilometres per second (37 miles per second), providing the first direct observation of the collision of two solar system objects. The collision resulted in disruptions in Jupiter's atmosphere, such as plumes and bubbles of gas, and dark spots in the atmosphere which remained visible for several months.

The event was closely observed and recorded by astronomers worldwide as a result of its tremendous scientific importance, and also generated a large amount of coverage in the popular media. The event highlighted Jupiter's role in reducing the amount of space debris in the inner solar system, which is thought to be a prerequisite for unbroken development of life.

Astronomy Intro

Astronomy is the science of celestial objects and phenomena that originate outside Earth's atmosphere, such as stars, planets, comets, galaxies, and the cosmic background radiation. It is concerned with the formation and development of the universe, the evolution and physical and chemical properties of celestial objects and the calculation of their motions. Astronomical observations are not only relevant for astronomy as such, but provide essential information for the verification of fundamental theories in physics, such as general relativity theory. Complementary to observational astronomy, theoretical astrophysics seeks to explain astronomical phenomena.

Astronomy is one of the oldest sciences, with a scientific methodology existing at the time of Ancient Greece and advanced observation techniques possibly much earlier (see archaeoastronomy). Historically, amateurs 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.

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.