Astrophysics

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Posted by sonny 04/29/2009 @ 02:13

Tags : astrophysics, astronomy and space, sciences

News headlines
Refurbishments Complete, Astronauts Let Go of Hubble - New York Times
Robert Kirshner, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said of the telescope's cosmic postcards: “Those fantastic images communicate the joy of finding out how the world works. I think this seeps into everything — and it...
See stars, and enjoy it too - Times of India
The success stories that come from our own space research organizations have recently sparked the interest in many young minds who wish to pursue a career in space research and Astrophysics. Students still shy away from many areas in Astronomy,...
UNLV astrophysicist: In search of universal truth - Las Vegas Sun
Bing Zhang is an award-winning astrophysicist at UNLV, He studies gamma ray bursts, which generate more power in seconds than the sun does in billions of years. By Brendan Buhler Bing Zhang takes the long view, peering back sometimes as far as a...
Bounty of Space Telescopes Fuels Golden Age of Astronomy - Space.com
We have the largest set of assets in space for astronomers ever," said Jon Morse, NASA's Astrophysics Division Director. "It really is a golden era to be a practicing astronomer. It entices me to leave my desk job and go back to the field....
Distinguished prof. of astronomy named - Independent Collegian (subscription)
Bjorkman has secured many external funds for UT including the $500000 NASA Long-Term Space Astrophysics Grant. The NASA grant represents the highest caliber of research done in the field of astrophysics. Bjorkman said she has one specific thing she...
New Way Of Reading Light With Help Locate Earth-like Planets ... - Science Daily (press release)
Now researchers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. have created an "astro-comb" to help astronomers detect lighter planets, more like Earth, around distant stars. The Harvard group will present their findings at the...
Stargazing Notes — Failed stars - Penticton Western
Ken Tapping is an astronomer with the National Research Council's Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory in Penticton. Stars are formed when cosmic gas clouds, which are composed mainly of...
Simulate Star Clusters with Second Life Mod - Wired News
Other astrophysics simulators are out there, and some are much more detailed, but this is the first that gives users the god-like power to control and share the simulation in real time. “The interactivity is just built into these virtual worlds,” Farr...
NASA Announces 2009 Astronomy and Astrophysics Fellows - Elites TV
NASA has selected fellows in three areas of astronomy and astrophysics for its Einstein, Hubble, and Sagan Fellowships. The recipients of this year's post-doctoral fellowships will conduct independent research at institutions around the country....
Harvard-Smithsonian research physicist Dr. Kate Kirby named new ... - PhysicsToday.org
From 1988 to 2001, she served as an Associate Director at the Harvard-Smithsonian Center for Astrophysics, heading the Atomic and Molecular Physics Division. In 2001, she was appointed Director of the National Science Foundation-funded Institute for...

Astrophysics

NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant

Astrophysics (lang-el: Astro - meaning "stare", and lang-el: physis – φύσις meaning "nature") is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as galaxies, stars, planets, exoplanets, and the interstellar medium, as well as their interactions. The study of cosmology is theoretical astrophysics at scales much larger than the size of particular gravitationally-bound objects in the universe.

Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. In practice, modern astronomical research involves a substantial amount of physics. The name of a university's department ("astrophysics" or "astronomy") often has to do more with the department's history than with the contents of the programs. Astrophysics can be studied at the bachelors, masters, and Ph.D. levels in aerospace engineering, physics, or astronomy departments at many universities.

Although astronomy is as ancient as recorded history itself, it was long separated from the study of physics. In the Aristotelian worldview, the celestial world tended towards perfection—bodies in the sky seemed to be perfect spheres moving in perfectly circular orbits—while the earthly world seemed destined to imperfection; these two realms were not seen as related.

Aristarchus of Samos (c. 310–250 BC) first put forward the notion that the motions of the celestial bodies could be explained by assuming that the Earth and all the other planets in the Solar System orbited the Sun. Unfortunately, in the geocentric world of the time, Aristarchus' heliocentric theory was deemed outlandish and heretical, and for centuries, the apparently common-sense view that the Sun and other planets went round the Earth nearly went unquestioned until the development of Copernican heliocentrism in the 16th century AD. This was due to the dominance of the geocentric model developed by Ptolemy (c. 83-161 AD), an Hellenized astronomer from Roman Egypt, in his Almagest treatise.

The only known supporter of Aristarchus was Seleucus of Seleucia, a Babylonian astronomer who is said to have proved heliocentrism through reasoning in the 2nd century BC. This may have involved the phenomenon of tides, which he correctly theorized to be caused by attraction to the Moon and notes that the height of the tides depends on the Moon's position relative to the Sun. Alternatively, he may have determined the constants of a geometric model for the heliocentric theory and developed methods to compute planetary positions using this model, possibly using early trigonometric methods that were available in his time, much like Copernicus. Some have also interpreted the planetary models developed by Aryabhata (476-550), an Indian astronomer, and Albumasar (787-886), a Persian astronomer, to be heliocentric models.

In the 9th century AD, the Persian physicist and astronomer, Ja'far Muhammad ibn Mūsā ibn Shākir, hypothesized that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who believed that the celestial spheres followed their own set of physical laws different from that of Earth. He also proposed that there is a force of attraction between "heavenly bodies", vaguely foreshadowing the law of gravity.

After heliocentrism was revived by Nicolaus Copernicus in the 16th century, Galileo Galilei discovered the four brightest moons of Jupiter in 1609, and documented their orbits about that planet, which contradicted the geocentric dogma of the Catholic Church of his time, and escaped serious punishment only by maintaining that his astronomy was a work of mathematics, not of natural philosophy (physics), and therefore purely abstract.

The availability of accurate observational data (mainly from the observatory of Tycho Brahe) led to research into theoretical explanations for the observed behavior. At first, only empirical rules were discovered, such as Kepler's laws of planetary motion, discovered at the start of the 17th century. Later that century, Isaac Newton bridged the gap between Kepler's laws and Galileo's dynamics, discovering that the same laws that rule the dynamics of objects on Earth rule the motion of planets and the moon. Celestial mechanics, the application of Newtonian gravity and Newton's laws to explain Kepler's laws of planetary motion, was the first unification of astronomy and physics.

After Isaac Newton published his book, Philosophiæ Naturalis Principia Mathematica, maritime navigation was transformed. Starting around 1670, the entire world was measured using essentially modern latitude instruments and the best available clocks. The needs of navigation provided a drive for progressively more accurate astronomical observations and instruments, providing a background for ever more available data for scientists.

At the end of the 19th century, it was discovered that, when decomposing the light from the Sun, a multitude of spectral lines were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique chemical elements. In this way it was proved that the chemical elements found in the Sun (chiefly hydrogen) were also found on Earth. Indeed, the element helium was first discovered in the spectrum of the Sun and only later on Earth, hence its name. During the 20th century, spectroscopy (the study of these spectral lines) advanced, particularly as a result of the advent of quantum physics that was necessary to understand the astronomical and experimental observations.

The majority of astrophysical observations are made using the electromagnetic spectrum.

Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere.

Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.

The study of our own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Our understanding of our own sun serves as a guide to our understanding of other stars.

Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.

Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Topics studied by theoretical astrophysicists include: stellar dynamics and evolution; galaxy formation; magnetohydrodynamics; large-scale structure of matter in the Universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Astrophysical relativity serves as a tool to gauge the properties of large scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.

Some widely accepted and studied theories and models in astrophysics, now included in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, dark energy and fundamental theories of physics.

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Astrophysics Data System

Logo of the ADS

The NASA Astrophysics Data System (usually referred to as ADS) is an online database of over 7,000,000 astronomy and physics papers from both peer reviewed and non-peer reviewed sources. Abstracts are available free online for almost all articles, and full scanned articles are available in GIF and PDF format for older articles. New articles have links to electronic versions hosted at the journal's webpage, but these are typically available only by subscription (which most astronomy research facilities have). It is managed by the Harvard-Smithsonian Center for Astrophysics.

ADS is an extremely powerful research tool, and has had a significant impact on the efficiency of astronomical research since it was launched in 1992. Literature searches which previously would have taken days or weeks can now be carried out in seconds via the sophisticated ADS search engine, which is custom-built for astronomical needs. Studies have found that the benefit to astronomy of the ADS is equivalent to several hundred million US dollars annually, and the system is estimated to have tripled the readership of astronomical journals.

Use of ADS is almost universal among astronomers worldwide, and therefore ADS usage statistics can be used to analyse global trends in astronomical research. These studies have revealed that the amount of research an astronomer carries out is related to the GDP per capita of the country in which they are based and that the number of astronomers in a country is proportional to the GDP of that country, so the amount of research done in a country is proportional to the square of its GDP divided by its population.

For many years, a growing problem in astronomical research was that the number of papers published in the major astronomical journals was increasing steadily, meaning astronomers were able to read less and less of the latest research findings. During the 1980s, astronomers saw that the nascent technologies which formed the basis of the Internet could eventually be used to build an electronic indexing system of astronomical research papers which would allow astronomers to keep abreast of a much greater range of research.

The first suggestion of a database of journal paper abstracts was made at a conference on Astronomy from Large Data-bases held in Garching bei München in 1987. Initial development of an electronic system for accessing astrophysical abstracts took place during the following two years, and in 1991 discussions took place on how to integrate ADS with the SIMBAD database, which contains all available catalogue designations for objects outside the solar system, to create a system where astronomers could search for all the papers written about a given object.

An initial version of ADS, with a database consisting of 40 papers, was created as a proof of concept in 1988, and the ADS database was successfully connected with the SIMBAD database in the summer of 1993. The creators believed this was the first use of the Internet to allow simultaneous querying of transatlantic scientific databases. Until 1994, the service was available via proprietary network software, but was transferred to the nascent World Wide Web early that year. The number of users of the service quadrupled in the five weeks following the introduction of the ADS web-based service.

At first, the journal articles available via ADS were scanned bitmaps created from the paper journals, but from 1995 onwards, the Astrophysical Journal began to publish an on-line edition, soon followed by the other main journals such as Astronomy and Astrophysics and the Monthly Notices of the Royal Astronomical Society. ADS provided links to these electronic editions from their first appearance. Since about 1995, the number of ADS users has doubled roughly every two years. ADS now has agreements with almost all astronomical journals, who supply abstracts. Scanned articles from as far back as the early 19th century are available via the service, which now contains over five million documents. The service is distributed worldwide, with twelve mirror sites in twelve countries on five continents, with the database synchronised by means of weekly updates using rsync, a mirroring utility which allows updates to only the portions of the database which have changed. All updates are triggered centrally, but they initiate scripts at the mirror sites which "pull" updated data from the main ADS servers.

Papers are indexed within the database by their bibliographic record, containing the details of the journal they were published in and various associated metadata, such as author lists, references and citations. Originally this data was stored in ASCII format, but eventually the limitations of this encouraged the database maintainers to migrate all records to an XML (Extensible Markup Language) format in 2000. Bibliographic records are now stored as an XML element, with sub-elements for the various metadata.

Since the advent of online editions of journals, abstracts are loaded into the ADS on or before the publication date of articles, with the full journal text available to subscribers. Older articles have been scanned, and an abstract is created using optical character recognition software. Scanned articles from before about 1995 are usually available free, by agreement with the journal publishers.

Scanned articles are stored in TIFF format, at both medium and high resolution. The TIFF files are converted on demand into GIF files for on-screen viewing, and PDF or PostScript files for printing. The generated files are then cached to eliminate needlessly frequent regenerations for popular articles. As of 2000, ADS contained 250 GB of scans, which consisted of 1,128,955 article pages comprising 138,789 articles. By 2005 this had grown to 650 GB, and is expected to grow further, to about 900 GB by 2007. No further information has been published.

The database initially contained only astronomical references, but has now grown to incorporate three databases, covering astronomy (including planetary sciences and solar physics) references, physics (including instrumentation and geosciences) references, as well as preprints of scientific papers from arXiv. The astronomy database is by far the most advanced and its use accounts for about 85% of the total ADS usage. Articles are assigned to the different databases according to the subject rather than the journal they are published in, so that articles from any one journal might appear in all three subject databases. The separation of the databases allows searching in each discipline to be tailored, so that words can automatically be given different weight functions in different database searches, depending on how common they are in the relevant field.

Data in the preprint archive is updated daily from the arXiv, the main repository of physics and astronomy preprints. The advent of preprint servers has, like ADS, had a significant impact on the rate of astronomical research, as papers are often made available from preprint servers weeks or months before they are published in the journals. The incorporation of preprints from the arXiv into ADS means that the search engine can return the most current research available, with the caveat that preprints may not have been peer reviewed or proofread to the required standard for publication in the main journals. ADS's database links preprints with subsequently published articles wherever possible, so that citation and reference searches will return links to the journal article where the preprint was cited.

The software which runs the system was written specifically for it, allowing for extensive customisation to astronomical needs which would not have been possible with general purpose database software. The scripts are designed to be as platform independent as possible, given the need to facilitate mirroring on different systems around the world, although the growing dominance of Linux as the operating system of choice within astronomy has led to increasing optimisation of the scripts for installation on that platform.

The main ADS server is located at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and is a single PC with two 3.6 GHz CPUs and 6 GB of RAM, running the Fedora Core Linux distribution. Mirrors are located in Argentina, Brazil, China, Chile, France, Germany, India, Japan, Russia, South Korea and the United Kingdom.

ADS currently receive abstracts or tables of contents from almost two hundred journal sources. The service may receive data referring to the same article from multiple sources, and creates one bibliographic reference based on the most accurate data from each source. The common use of TeX and LaTeX by almost all scientific journals greatly facilitates the incorporation of bibliographic data into the system in a standardised format, and importing HTML-coded web-based articles is also simple. ADS utilises Perl scripts for importing, processing and standardising bibliographic data.

The apparently mundane task of converting author names into a standard Surname, Initial format is actually one of the more difficult to automate, due to the wide variety of naming conventions around the world and the possibility that a given name such as Davis could be a first name, middle name or surname. The accurate conversion of names requires a detailed knowledge of the names of authors active in astronomy, and ADS maintains an extensive database of author names, which is also used in searching the database (see below).

For electronic articles, a list of the references given at the end of the article is easily extracted. For scanned articles, reference extraction relies on OCR. The reference database can then be "inverted" to list the citations for each paper in the database. Citation lists have been used in the past to identify popular articles missing from the database; mostly these were from before 1975 and have now been added to the system.

The database now contains over seven million articles. In the cases of the major journals of astronomy (Astrophysical Journal, Astronomical Journal, Astronomy and Astrophysics, Publications of the Astronomical Society of the Pacific and the Monthly Notices of the Royal Astronomical Society), coverage is complete, with all issues indexed from number 1 to the present. These journals account for about two-thirds of the papers in the database, with the rest consisting of papers published in over 100 other journals from around the world.

While the database contains the complete contents of all the major journals and many minor ones as well, its coverage of references and citations is much less complete. References in and citations of articles in the major journals are fairly complete, but references such as "private communication", "in press" or "in preparation" cannot be matched, and author errors in reference listings also introduce potential errors. Astronomical papers may cite and be cited by articles in journals which fall outside the scope of ADS, such as chemistry, maths or biology journals.

Since its inception, the ADS has developed a highly sophisticated search engine to query the abstract and object databases. The search engine is tailor-made for searching astronomical abstracts, and the engine and its user interface assume that the user is well-versed in astronomy and able to interpret search results which are designed to return more than just the most relevant papers. The database can be queried for author names, astronomical object names, title words, and words in the abstract text, and results can be filtered according to a number of criteria. It works by first gathering synonyms and simplifying search terms as described above, and then generating an "inverted file", which is a list of all the documents matching each search term. The user-selected logic and filters are then applied to this inverted list to generate the final search results.

The capability to search for papers on specific astronomical objects is one of ADS's most powerful tools. The system uses data from the SIMBAD, the NASA/IPAC Extragalactic Database, the International Astronomical Union Circulars and the Lunar and Planetary Institute to identify papers referring to a given object, and can also search by object position, listing papers which concern objects within a 10 arcminute radius of a given Right Ascension and Declination. These databases combine the many catalogue designations an object might have, so that a search for the Pleiades will also find papers which list the famous open cluster in Taurus under any of its other catalogue designations or popular names, such as M45, the Seven Sisters or Melotte 22.

The search engine first filters search terms in several ways. An M followed by a space or hyphen has the space or hyphen removed, so that searching for Messier catalogue objects is simplified and a user input of M45, M 45 or M-45 all result in the same query being executed; similarly, NGC designations and common search terms such as Shoemaker Levy and T Tauri are stripped of spaces. Unimportant words such as AT, OR and TO are stripped out, although in some cases case sensitivity is maintained, so that while and is ignored, And is converted to "Andromedae", and Her is converted to "Herculis", but her is ignored.

Once search terms have been pre-processed, the database is queried with the revised search term, as well as synonyms for it. As well as simple synonym replacement such as searching for both plural and singular forms, ADS also searches for a large number of specifically astronomical synonyms. For example, spectrograph and spectroscope have basically the same meaning, and in an astronomical context metallicity and abundance are also synonymous. ADS's synonym list was created manually, by grouping the list of words in the database according to similar meanings.

As well as English language synonyms, ADS also searches for English translations of foreign search terms and vice versa, so that a search for the French word soleil retrieves references to Sun, and papers in languages other than English can be returned by English search terms.

Synonym replacement can be disabled if required, so that a rare term which is a synonym of a much more common term (such as 'dateline' rather than 'date') can be searched for specifically.

The search engine allows selection logic both within fields and between fields. Search terms in each field can be combined with OR, AND, simple logic or Boolean logic, and the user can specify which fields must be matched in the search results. This allows complex searches to be built; for example, the user could search for papers concerning NGC 6543 OR NGC 7009, with the paper titles containing (radius OR velocity) AND NOT (abundance OR temperature).

Search results can be filtered according to a number of criteria, including specifying a range of years such as '1945 to 1975', '2000 to the present day' or 'before 1900', and what type of journal the article appears in – non-peer reviewed articles such as conference proceedings can be excluded or specifically searched for, or specific journals can be included in or excluded from the search.

Although it was conceived as a means of accessing abstracts and papers, ADS provides a substantial amount of ancillary information along with search results. For each abstract returned, links are provided to other papers in the database which are referenced, and which cite the paper, and a link is provided to a preprint, where one exists. The system also generates a link to 'also-read' articles – that is, those which been most commonly accessed by those reading the article. In this way, an ADS user can determine which papers are of most interest to astronomers who are interested in the subject of a given paper.

Also returned are links to the SIMBAD and/or NASA Extragalactic Database object name databases, via which a user can quickly find out basic observational data about the objects analysed in a paper, and find further papers on those objects.

ADS is an almost universally used research tool among astronomers, and its impact on astronomical research is considerable. Several studies have estimated quantitatively how much more efficient ADS has made astronomy; one estimated that ADS increased the efficiency of astronomical research by 333 full-time equivalent research years per year, and another found that in 2002 its effect was equivalent to 736 full-time researchers, or all the astronomical research done in France. ADS has allowed literature searches that would previously have taken days or weeks to carry out to be completed in seconds, and it is estimated that ADS has increased the readership and use of the astronomical literature by a factor of about three since its inception.

In monetary terms, this increase in efficiency represents a considerable amount. There are about 12,000 active astronomical researchers worldwide, so ADS is the equivalent of about 5% of the working population of astronomers. The global astronomical research budget is estimated at between 4,000 and 5,000 million USD, so the value of ADS to astronomy would be about 200–250 million USD annually. Its operating budget is a small fraction of this amount.

The great importance of ADS to astronomers has been recognised by the United Nations, the General Assembly of which has commended ADS on its work and success, particularly noting its importance to astronomers in the developing world, in reports of the United Nations Committee on the Peaceful Uses of Outer Space. A 2002 report by a visiting committee to the Center for Astrophysics, meanwhile, said that the service had "revolutionized the use of the astronomical literature", and was "probably the most valuable single contribution to astronomy research that the CfA has made in its lifetime".

Because it is used almost universally by astronomers, ADS can reveal much about how astronomical research is distributed around the world. Most users of the system will reach from institutes of higher education, whose IP address can easily be used to determine the user's geographical location. Studies reveal that the highest per-capita users of ADS are France and Netherlands-based astronomers, and while more developed countries (measured by GDP per capita) use the system more than less developed countries; the relationship between GDP per capita and ADS use is not linear. The range of ADS uses per capita far exceeds the range of GDPs per capita, and basic research carried out in a country, as measured by ADS usage, has been found to be proportional to the square of the country's GDP divided by its population.

ADS usage statistics also suggest that astronomers in more developed countries tend to be more productive than those in less developed countries. The amount of basic research carried out is proportional to the number of astronomers in a country multiplied by the GDP per capita. Statistics also imply that astronomers in European cultures carry out about three times as much research as those in Asian cultures, perhaps suggesting cultural differences in the importance attached to astronomical research.

ADS has also been used to show that the fraction of single-author astronomy papers has decreased substantially since 1975 and that astronomical papers with more than 50 authors have become more common since 1990.

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Astronomy and Astrophysics

Astronomy and Astrophysics (abbreviated as A&A in the astronomical literature, or else Astron. Astrophys.) is a European Journal, publishing papers on theoretical, observational and instrumental astronomy and astrophysics. It was published by Springer-Verlag from 1969-2000, while EDP Sciences published the companion A&A Supplement Series. In 2000, the two journals merged, with the combined journal known simply as Astronomy and Astrophysics, and published by EDP Sciences. The journal copyright is owned by the European Southern Observatory.

A&A is one of the major journals of astronomy, alongside the Astrophysical Journal, Astronomical Journal and the Monthly Notices of the Royal Astronomical Society. While the first two are often the preferred journal of US-based researchers and the MNRAS is often the favoured journal for UK- and Commonwealth-based astronomers, A&A tends to be the preferred journal of astronomers based in Europe (excluding the UK), particularly since page charges are waived for astronomers working in member countries.

The original member countries were the four countries whose journals merged to form A&A (France, Germany, the Netherlands and Sweden) together with Belgium, Denmark, Finland and Norway. ESO also participated as a 'member country'. Norway later withdrew, but Austria, Greece, Italy, Spain and Switzerland all joined. The Czech Republic, Estonia, Hungary, Poland and Slovakia all joined as new members in the 1990s. In 2001 the words "A European Journal" were removed from the front cover in recognition of the fact that the journal was becoming increasingly global in scope, and in 2002 Argentina was admitted as an 'observer'. In 2004 the Board of Directors decided that "A&A will henceforth consider applications for sponsoring membership from any country in the world with well-documented active and excellent astronomical research". Argentina became the first non-European country to gain full membership in 2005. Brazil, Chile and Portugal all gained 'observer' status at this time and have since progressed to full membership.

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Atomic and Molecular astrophysics

Within a few million years the light from bright stars will have boiled away this molecular cloud of gas and dust. The cloud has broken off from the Carina Nebula. Newly formed stars are visible nearby, their images reddened by blue light being preferentially scattered by the pervasive dust. This image spans about two light years and was taken by the orbiting Hubble Space Telescope in 1999.

Atomic astrophysics is concerned with performing atomic physics calculations that will be useful to astronomers and using atomic data to interpret astronomical observations. Atomic physics plays a key role in astrophysics as astronomers' only information about a particular object comes through the light that it emits, and this light arises through atomic transitions.

Molecular astrophysics concerns the study of emission from molecules in space. There are 110 currently known interstellar molecules. These molecules have large numbers of observable transitions. Lines may also be observed in absorption--for example the highly redshifted lines seen against the gravitationally lensed quasar PKS1830-211. High energy radiation, such as ultraviolet light, can break the molecular bonds which hold atoms in molecules. In general then, molecules are found in cool astrophysical environments. The most massive objects in our Galaxy are giant clouds of molecules and dust, creatively named Giant Molecular Clouds. In these clouds, and smaller versions of them, stars and planets are formed. One of the primary fields of study of molecular astrophysics then, is star and planet formation. Molecules may be found in many environments, however, from stellar atmospheres to those of planetary satellites. Most of these locations are cool, and molecular emission is most easily studied via photons emitted when the molecules make transitions between low rotational energy states. One molecule, composed of the abundant carbon and oxygen atoms, and very stable against dissociation into atoms, is carbon monoxide, CO. The wavelength of the photon emitted when the CO molecule falls from its lowest excited state to its zero energy, or ground, state is 2.6mm, or 115 gigahertz (billion hertz). This frequency is a thousand times higher than typical FM radio frequencies. At these high frequencies, molecules in the Earth's atmosphere can block transmissions from space, and telescopes must be located in dry (water is an important atmospheric blocker), high sites. Radio telescopes must have very accurate surfaces to produce high fidelity images.

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Source : Wikipedia