Astrophysics Data SystemFrom Wikipedia, the free encyclopediaAstrophysics Data SystemADS logo.pngLogo of the ADSProducer HarvardSmithsonian Center for Astrophysics for the National Aeronautics and Space Administration (United States)History 1992 to presentAccessCost FreeCoverageDisciplines astronomy and physicsRecord depth Index & abstract & full-textGeospatial coverage WorldwideLinksWebsiteThe Astrophysics Data System (ADS), developed by the National Aeronautics and Space Administration (NASA), is an online database of over eight million 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 Graphics Interchange Format (GIF) and Portable Document Format (PDF) 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 HarvardSmithsonian Center for Astrophysics.ADS is a powerful research tool and has had a significant impact on the efficiency of astronomical research since it was launched in 1992. Literature searches that previously would have taken days or weeks can now be carried out in seconds via the ADS search engine, 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,[1] and the system is estimated to have tripled the readership of astronomical journals.[2]Use of ADS is almost universal among astronomers worldwide, and therefore ADS usage statistics can be used to analyze global trends in astronomical research. These studies have revealed that the amount of research an astronomer carries out is related to the per capita gross domestic product (GDP) of the country in which he/she is based, and that the number of astronomers in a country is proportional to the GDP of that country, so the total amount of research done in a country is proportional to the square of its GDP divided by its population.[2]Contents1 History2 Data in the system3 Software and hardware4 Indexing5 Coverage6 Search engine6.1 Author name queries6.2 Object name searches6.3 Title and abstract searches6.4 Synonym replacement6.5 Selection logic6.6 Result filtering7 Search results8 Impact on astronomy9 Sociological studies using ADS10 See also11 References12 External linksHistory[edit]For many years, a growing problem in astronomical research (as in other academic disciplines) 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.[3]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 Mnchen in 1987. Initial development of an electronic system for accessing astrophysical abstracts took place during the following two years; in 1991 discussions took place on how to integrate ADS with the SIMBAD database, containing all available catalog designations for objects outside the solar system, to create a system where astronomers could search for all the papers written about a given object.[1]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 it 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.[1]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 eight million documents. The service is distributed worldwide, with twelve mirror sites in twelve countries on five continents, with the database synchronized 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.[4]Data in the system[edit]1284 papers about M101 are available through ADS, from as long ago as 1850.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.[4]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.[5]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.[5] 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.[4]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.[6]Software and hardware[edit]The software runs on a system that was written specifically for it, allowing for extensive customization for astronomical needs that 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 use of Linux as the operating system of choice within astronomy has led to increasing optimization of the scripts for installation on that platform.[4]The main ADS server is located at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and is a dual 64-bit X86 Intel server with two quad-core 3.0 GHz CPUs and 32 GB of RAM, running the CentOS 5.4 Linux distribution.[5] Mirrors are located in Brazil, China, Chile, France, Germany, India, Indonesia, Japan, Russia, South Korea, United Kingdom, and the Ukraine.[7]Indexing[edit]ADS currently receives 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 standardized format, and importing HTML-coded web-based articles is also simple. ADS utilizes Perl scripts for importing, processing and standardizing bibliographic data.[4]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.Coverage[edit]The database now contains over eight 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, as well as in conference proceedings.[5]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, mathematics or biology journals.[8]Search engine[edit]An example of a complex search combining object, title and abstract queries with a date filterSince its inception, the ADS has developed a highly complex 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.[9]Author name queries[edit]The system indexes author names by surname and initials, and accounts for the possible variations in spelling of names using a list of variations. This is common in the case of names including accents such as umlauts and transliterations from Arabic or Cyrillic script. An example of an entry in the author synonym list is:AFANASJEV, VAFANASEV, VAFANASIEV, VAFANASEV, VAFANASYEV, VAFANSIEV, VAFANSEV, VObject name searches[edit]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 catalog designations or popular names, such as M45, the Seven Sisters or Melotte 22.[10]Title and abstract searches[edit]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.[11]Synonym replacement[edit]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.[4]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.Selection logic[edit]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).Result filtering[edit]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.Search results[edit]Search results page from ADS A, F, G, C, R etc. are links to associated data for each abstract such as full-text article, citations, also-read papers and so on.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 have 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.[9]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 analyzed in a paper, and find further papers on those objects.Impact on astronomy[edit]ADS is almost universally used as a research tool among astronomers, and there are several studies that 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,[1] and another found that in 2002 its effect was equivalent to 736 full-time researchers, or all the astronomical research done in France.[2] 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.[2]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,[12] so the value of ADS to astronomy would be about 200250 million USD annually. Its operating budget is a small fraction of this amount.[2]The great importance of ADS to astronomers has been recognized 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".[13]Sociological studies using ADS[edit]Because it is used almost universally by astronomers, ADS can reveal much about how astronomical research is distributed around the world. Most users access the system 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 usage 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.[2]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.[2]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.[14]See also[edit]BibcodeNASA/IPAC Extragalactic Database (NED)NASA Planetary Data System (PDS)PubMedSIMBADMichael J. KurtzReferences[edit]^ a b c d Kurtz, M.J.; Eichhorn G.; Accomazzi A.; Grant C.S.; Murray S.S.; Watson J.M. (2000). "The NASA Astrophysics Data System: Overview". Astronomy and Astrophysics Supplement 143 (1): 4159. arXiv:astro-ph/0002104. Bibcode:2000A&AS..143...41K. doi:10.1051/aas:2000170.^ a b c d e f g Kurtz, M.J.; Eichhorn G.; Accomazzi A.; Grant C.S.; Demleitner M.; Murray S.S. (2005). "Worldwide Use and Impact of the NASA Astrophysics Data System Digital Library". The Journal of the American Society for Information Science and Technology 56 (1): 36. arXiv:0909.4786. Bibcode:2005JASIS..56...36K. doi:10.1002/asi.20095. (Preprint)^ Good, J. C. (1992). Diana M. Worrall, Chris Biemesderfer and Jeannette Barnes, ed. "Overview of the Astrophysics Data System (ADS), Astronomical Data Analysis Software and Systems I". A.S.P. Conference Series 25: 35.^ a b c d e f Accomazzi, A.; Eichhorn G.; Kurtz M.J.; Grant C.S.; Murray S.S. (2000). "The NASA Astrophysics Data System: Architecture". Astronomy and Astrophysics Supplement 143 (1): 85109. arXiv:astro-ph/0002105. Bibcode:2000A&AS..143...85A. doi:10.1051/aas:2000172.^ a b c d "NASA ADS Abstract Service Mirroring Information". Harvard-Smithsonian Center for Astrophysics. 23 June 2005. Retrieved 2008-11-02.^ "APS - 2007 APS March Meeting - Event - myADS-arXiv: A fully customized, open access virtual journal". meetings.aps.org. Retrieved 2008-10-30.^ "SAO/NASA ADS at SAO: Mirror Sites". doc.adsabs.harvard.edu. Retrieved 2008-10-30.^ "ADS Bibliographic Codes: Journal Abbreviations". adsabs.harvard.edu. Retrieved 2008-10-30.^ a b Eichhorn, G.; Kurtz M.J.; Accomazzi A.; Grant C.S.; Murray S.S. (2000). "The NASA Astrophysics Data System: The search engine and its user interface". Astronomy and Astrophysics Supplement 143 (1): 6183. arXiv:astro-ph/0002102. Bibcode:2000A&AS..143...61E. doi:10.1051/aas:2000171.^ "SAO/NASA ADS HELP: Abstract Query Form Position". doc.adsabs.harvard.edu. Retrieved 2008-10-30.^ "SAO/NASA ADS HELP: Abstract Query Form Stop". doc.adsabs.harvard.edu. Retrieved 2008-10-30.^ Woltjer, L. (1998). "Economic Consequences of the Deterioration of the Astronomical Environment". ASP Conference Series 139, Preserving the Astronomical Windows: 243.^ "ADS Awards and Recognition". NASA ADS. Retrieved 2008-11-02.^ Schulman, E.; French J.C.; Powell A.L.; Eichhorn G.; Kurtz M.J.; Murray S.S. (1997). "Trends in Astronomical Publication Between 1975 and 1996". Publications of the Astronomical Society of the Pacific 109: 12781284. Bibcode:1997PASP..109.1278S. doi:10.1086/134008.External links[edit]HarvardSmithsonian Center for AstrophysicsFrom Wikipedia, the free encyclopediaHarvardSmithsonian Center for AstrophysicsCenter for Astrophysics.jpgExterior view of the CfA.Established 1973Mission To advance knowledge and understanding of the universe through research and education in astronomy and astrophysicsDirector Charles R. AlcockLocation Cambridge, Massachusetts, United StatesAddress 60 Garden St.Website Official websiteThe HarvardSmithsonian Center for Astrophysics (CfA) is one of the largest and most diverse astrophysical institutions in the world,[citation needed] where scientists carry out a broad program of research in astronomy, astrophysics, earth and space sciences, and science education. The center's mission is to advance knowledge and understanding of the universe through research and education in astronomy and astrophysics.The center was founded in 1973 as a joint venture between the Smithsonian Institution and Harvard University. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The center's main facility is located between Concord Avenue and Garden Street, with its mailing address and main entrance at 60 Garden Street, Cambridge, Massachusetts. Beyond this location there are also additional satellite facilities elsewhere around the globe. The current director of the CfA, Charles R. Alcock, was named in 2004.[1] The director from 1982 to 2004 was Irwin I. Shapiro.[2]Contents1 Ground-based observatories2 Space-based observatories3 Plans4 Directors5 Funding sources6 Trivia7 References8 External linksGround-based observatories[edit]Fred Lawrence Whipple ObservatoryMagellan telescopesMMT ObservatorySouth Pole TelescopeSubmillimeter Array1.2-Meter Millimeter-Wave TelescopeVery Energetic Radiation Imaging Telescope Array System (VERITAS)Space-based observatories[edit]Chandra X-ray ObservatoryHinodeKeplerSolar Dynamics Observatory (SDO)Solar and Heliospheric Observatory (SOHO)Spitzer Space TelescopePlans[edit]Giant Magellan TelescopeMurchison Widefield ArraySquare Kilometer ArrayPan-STARRSLarge Synoptic Survey TelescopeConstellation-X ObservatoryDirectors[edit]George B. Field: 19731982Irwin I. Shapiro: 19822004Charles R. Alcock: 2004PresentFunding sources[edit]In FY2010, expenditures by funding source were as follows:NASA: 70%Smithsonian federal funds: 22%National Science Foundation: 4%United States Department of Energy: 1%Annenberg Foundation: 1%Gifts and endowments: 1%Other: 1%Trivia[edit]The asteroid 10234 Sixtygarden is named after the Center's address.[3][4]References[edit]^ "Alcock to lead the CfA: Astrophysicist noted for 'dark matter' studies to take helm at observatories". Harvard Gazette. 2004-05-20. Retrieved 2007-12-25.^ "Harvard-Smithsonian Center for Astrophysics Celebrates 25 Years". Harvard University Gazette. 1998-10-15. Retrieved 2007-02-26.^ "(10234) Sixtygarden". Klet Observatory. 1999-11-23. Retrieved 2007-12-25.^ "Discovery Circumstances: Numbered Minor Planets (10001)-(15000)". Central Bureau for Astronomical Telegrams (CBAT) and Minor Planet Center (MPC). Retrieved 2007-12-25.External links[edit]CfA Homepagev t eHarvard University Harvard University History John Harvard President Drew Gilpin Faust Board of Overseers The President and Fellows of Harvard College Provost Alan M. Garber The Harvard LibraryJohn Harvard statue.jpgArts andSciences Harvard Faculty of Arts and Sciences Dean Michael D. SmithCollegeHarvard College Dean Rakesh Khurana Radcliffe CollegeFreshman dormitories Upperclass houses Adams Cabot Currier Dudley Dunster Eliot Kirkland Leverett Lowell Mather Pforzheimer Quincy WinthropUndergraduate organizations The Harvard Crimson The Harvard Lampoon The Harvard Advocate The Harvard IndependentAthletics: Harvard Crimson Ivy League Harvard Stadium Yale football rivalry Lavietes Pavilion Bright Hockey Center Cornell hockey Rivalry Beanpot Weld BoathouseContinuingEducationDivision of Continuing Education Dean Huntington D. Lambert Extension School Summer School History of Harvard Extension SchoolEng.?&?Appl.SciencesJohn A. 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Sackler Fogg Museum of Art Busch-Reisinger Museum of Natural History Glass Flowers Mineralogical Museum Herbaria Comparative Zoology Peabody Museum of Archaeology and Ethnology Semitic MuseumCambridgecampusMemorial Hall Science Center Smith Campus Center Peabody Terrace Harvard Graduate Center Harvard Hall University Hall Memorial Church Choir Harvard Yard John Harvard statue Johnston GateCenters andinstitutesART Dumbarton Oaks Harvard Forest Health Science and Technology Radcliffe Institute for Advanced Study Schlesinger Library Real Colegio Complutense Wyss Institute for Biologically Inspired Engineering Commencement traditions Academic regalia Heraldry Tercentenary celebration Harvard University Professor Harvard Magazine Harvard Gazette Harvard University Pressv t eSmithsonian InstitutionMuseumsAfrican American History and Culture (under construction) African Art Air and Space UdvarHazy American Art American History American Indian Heye Center Anacostia Arts and Industries Castle CooperHewitt Design Freer Hirshhorn Numismatic Collection Natural History Barcode of Life Caribbean Coral Reef Global Volcanism Portrait Gallery Postal Renwick Sackler Zoological ParkResearchAmerican Art American Gardens Archives Astrophysics Conservation Biology Environmental Research Libraries Marine Station Museum Conservation Migratory Bird Tropical ResearchCulturalAsian Pacific Latino Folklife and Cultural Heritage Folklife Festival FolkwaysMediaAir & Space Smithsonian magazine Books Scholarly PressOtherAffiliations James Smithson Ripley Center Science Education Traveling ExhibitionAstrophysicsFrom Wikipedia, the free encyclopediaThis article is about the use of physics and chemistry to determine the nature of astronomical objects. For the use of physics to determine their positions and motions, see Celestial mechanics. For the physical study of the largest-scale structures of the universe, see Physical cosmology. For the journal, see The Astrophysical Journal.PhysicsAlbert Einstein's famous equation E = m c squaredMassenergy equivalenceHistory of physicsBranchesClassical mechanics Condensed matter physics Electromagnetism Optics Particle physics Quantum mechanics Relativity Statistical mechanics ThermodynamicsResearch fieldsApplied physics Astrophysics Atomic, molecular, and optical physics Biophysics Geophysics Nuclear physicsPast experiments2-degree-Field Galaxy Redshift Survey 2-Micron All-Sky Survey (2MASS) Bell test BOOMERanG Camera obscura experiments Cavendish experiment Cosmic Background Explorer (COBE) CowanReines neutrino experiment DavissonGermer Double-slit Foucault pendulum FranckHertz Gravity Probe A Gravity Probe B GeigerMarsden Homestake experiment MichelsonMorley Oil drop experiment Sloan Digital Sky Survey SternGerlach Wilkinson Microwave Anisotropy ProbeCurrent experimentsHadron Elektron Ring Anlage (HERA) James Webb Space Telescope Large Hadron Collider (LHC) Relativistic Heavy Ion ColliderScientistsBohr Dirac Einstein Feynman Galileo Hawking Heisenberg Maxwell Newton Pauli Rutherford Schrdinger Wignerv t eAstrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the heavenly bodies, rather than their positions or motions in space."[1][2] Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background.[3][4] Their emissions are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. 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 often involves a substantial amount of work in the realms of theoretical and observational physics. Highly elusive areas of study for astrophysicists, which are of immense interest to the public, include their attempts to determine: the properties of dark matter, dark energy, and black holes; whether or not time travel is possible, wormholes can form, or the multiverse exists; and the origin and ultimate fate of the universe.[3] Topics also studied by theoretical astrophysicists include: Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics.Astrophysics can be studied at the bachelors, masters, and Ph.D. levels in physics or astronomy departments at many universities.Contents1 History2 Observational astrophysics3 Theoretical astrophysics4 Popularization5 See also6 References7 Further reading8 External linksHistory[edit]Early 20th-century comparison of elemental, solar, and stellar spectraAlthough astronomy is as ancient as recorded history itself, it was long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its goal. Consequently, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere; either Fire as maintained by Plato, or Aether as maintained by Aristotle.[5][6] During the 17th century, natural philosophers such as Galileo,[7] Descartes,[8] and Newton[9] began to maintain that the celestial and terrestrial regions were made of similar kinds of material and were subject to the same natural laws.[10] Their challenge was that the tools had not yet been invented with which to prove these assertions.[11]For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects.[12][13] A new astronomy, soon to be called astrophysics, began to emerge when William Hyde Wollaston and Joseph von Fraunhofer independently discovered that, when decomposing the light from the Sun, a multitude of dark lines (regions where there was less or no light) were observed in the spectrum.[14] By 1860 the physicist, Gustav Kirchhoff, and the chemist, Robert Bunsen, had demonstrated that the dark lines in the solar spectrum corresponded to bright lines in the spectra of known gases, specific lines corresponding to unique chemical elements.[15] Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere.[16] In this way it was proved that the chemical elements found in the Sun and stars were also found on Earth.Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected bright, as well as dark, lines in solar spectra. Working with the chemist, Edward Frankland, to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements. He thus claimed the line represented a new element, which was called helium, after the Greek Helios, the Sun personified.[17][18]In 1885, Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, and Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme which was accepted for world-wide use in 1922.[19]In 1925 Cecilia Helena Payne (later Cecilia Payne-Gaposchkin) wrote an influential doctoral dissertation at Radcliffe College, in which she applied ionization theory to stellar atmospheres to relate the spectral classes to the temperature of stars.[20] Most significantly, she discovered that hydrogen and helium were the principal components of stars. This discovery was so unexpected that her dissertation readers convinced her to modify the conclusion before publication. However, later research confirmed her discovery.[21]By the end of the 20th century, further study of stellar and experimental spectra advanced, particularly as a result of the advent of quantum physics.[22]Observational astrophysics[edit]Supernova remnant LMC N 63A imaged in x-ray (blue), optical (green) and radio (red) wavelengths. The X-ray glow is from material heated to about ten million degrees Celsius by a shock wave generated by the supernova explosion.Observational astronomy is a division of the astronomical science that is concerned with recording data, in contrast with theoretical astrophysics, which is mainly concerned with finding out the measurable implications of physical models. It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.The majority of astrophysical observations are made using the electromagnetic spectrum.Radio astronomy studies radiation with a wavelength greater than a few millimeters. Example areas of study are radio waves, usually emitted by cold objects such as interstellar gas and dust clouds; the cosmic microwave background radiation which is the redshifted light from the Big Bang; pulsars, which were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.Infrared astronomy studies radiation with a wavelength that is too long to be visible to the naked eye but is shorter than radio waves. Infrared observations are usually made with telescopes similar to the familiar optical telescopes. Objects colder than stars (such as planets) are normally studied at infrared frequencies.Optical astronomy is the oldest kind of astronomy. Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this wavelength range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae.Ultraviolet, X-ray and gamma ray astronomy study very energetic processes such as binary pulsars, black holes, magnetars, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well. There are two methods in use to observe this part of the electromagnetic spectrumspace-based telescopes and ground-based imaging air Cherenkov telescopes (IACT). Examples of Observatories of the first type are RXTE, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory. Examples of IACTs are the High Energy Stereoscopic System (H.E.S.S.) and the MAGIC telescope.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 very 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.The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the HertzsprungRussell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction.Theoretical astrophysics[edit]The stream lines on this simulation of a supernova show the flow of matter behind the shock wave giving clues as to the origin of pulsarsTheoretical 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.[23][24]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 and evolution; 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. Wormholes are examples of hypotheses which are yet to be proven (or disproven).Popularization[edit]The roots of astrophysics can be found in the seventeenth century emergence of a unified physics, in which the same laws applied to the celestial and terrestrial realms.[10] There were scientists who were qualified in both physics and astronomy who laid the firm foundation for the current science of astrophysics. In modern times, young students continue to be drawn to astrophysics due to its popularization by notable educators such as prominent professors Subrahmanyan Chandrasekhar, Stephen Hawking, Hubert Reeves, Carl Sagan, Neil deGrasse Tyson and others. The efforts of the early, late, and present scientists continue to attract young people to study the history and science of astrophysics.[25][26][27]See also[edit]Portal icon Cosmology portalPortal icon Physics portalAstrochemistryAstronomical observatoriesAstronomical spectroscopyBremsstrahlungHenry Draper MedalHertzsprungRussell diagramHigh-energy astronomyIllustris projectImportant publications in astrophysicsList of astronomers (includes astrophysicists)NucleosynthesisNeutrino astronomy (future prospects)Particle acceleratorRadio astronomySpectroscopyStellar classificationStellar physicsTimeline of knowledge about galaxies, clusters of galaxies, and large-scale structureTimeline of white dwarfs, neutron stars, and supernovaeTimeline of black hole physicsTimeline of gravitational physics and relativityReferences[edit]^ Keeler, James E. (November 1897), "The Importance of Astrophysical Research and the Relation of Astrophysics to the Other Physical Sciences", The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics 6 (4): 271288, Bibcode:1897ApJ.....6..271K, doi:10.1086/140401, [Astrophysics] is closely allied on the one hand to astronomy, of which it may properly be classed as a branch, and on the other hand to chemistry and physics. It seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in spacewhat they are, rather than where they are.^ "astrophysics". Merriam-Webster, Incorporated. Archived from the original on 10 June 2011. Retrieved 2011-05-22.^ a b "Focus Areas - NASA Science". nasa.gov.^ "astronomy". Encyclopedia Britannica.^ Lloyd, G.E.R. (1968). Aristotle: The Growth and Structure of His Thought. Cambridge: Cambridge University Press. pp. 1345. ISBN 0-521-09456-9.^ Cornford, Francis MacDonald (c. 1957) [1937]. Plato's Cosmology: The Timaeus of Plato translated, with a running commentary. Indianapolis: Bobbs Merrill Co. p. 118.^ Galilei, Galileo (1989), Van Helden, Albert, ed., Sidereus Nuncius or The Sidereal Messenger, Chicago: University of Chicago Press, pp. 21, 47, ISBN 0-226-27903-0^ Edward Slowik (2013) [2005]. "Descartes' Physics". Stanford Encyclopedia of Philosophy. Retrieved 2015-07-18.^ Westfall, Richard S. (1980), Never at Rest: A Biography of Isaac Newton, Cambridge: Cambridge University Press, pp. 731732, ISBN 0-521-27435-4^ a b Burtt, Edwin Arthur (2003) [1924], The Metaphysical Foundations of Modern Science (second revised ed.), Mineola, NY: Dover Publications, pp. 30, 41, 2412, ISBN 9780486425511^ Ladislav Kvasz (2013). "Galileo, Descartes, and Newton Founders of the Language of Physics" (PDF). Institute of Philosophy, Academy of Sciences of the Czech Republic. Retrieved 2015-07-18.^ Case, Stephen (2015), "'Land-marks of the universe': John Herschel against the background of positional astronomy", Annals of Science 72 (4): 417434, doi:10.1080/00033790.2015.1034588, The great majority of astronomers working in the early nineteenth century were not interested in stars as physical objects. Far from being bodies with physical properties to be investigated, the stars were seen as markers measured in order to construct an accurate, detailed and precise background against which solar, lunar and planetary motions could be charted, primarily for terrestrial applications.^ Donnelly, Kevin (September 2014), "On the boredom