Astrophysics 361897 225299421 2008-07-12T23:32:57Z Rumping 4965639 kn: after ka: [[Image:NGC 4414 (NASA-med).jpg|right|thumb|280px|'''[[NGC 4414]]''', a typical [[spiral galaxy]] in the [[constellation]] [[Coma Berenices]], is about 56,000 [[light-year]]s in diameter and approximately 60 million light-years distant]] '''Astrophysics''' is the branch of [[astronomy]] that deals with the [[physics]] of the [[universe]], including the physical properties ([[luminosity]], [[density]], [[temperature]], and [[chemistry|chemical]] composition) of [[astronomical object|celestial object]]s such as [[star]]s, [[galaxy|galaxies]], and the [[interstellar medium]], as well as their interactions. The study of [[Physical cosmology|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]], [[theory of relativity| relativity]], [[nuclear physics|nuclear]] and [[particle physics]], and [[atomic, molecular, and optical physics|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 [[bachelor's degree|bachelors]], [[master's degree|masters]], and [[Doctor of Philosophy|Ph.D.]] levels in [[aerospace engineering]], physics, or astronomy departments at many [[university|universities]]. ==History== Although astronomy is as ancient as recorded history itself, it was long separated from the study of physics. In the [[Aristotel]]ian 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 [[planet]]s 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 [[Greek astronomy|Hellenized astronomer]] from [[History of Roman Egypt|Roman Egypt]], in his ''[[Almagest]]'' treatise. The only known supporter of Aristarchus was [[Seleucus of Seleucia]], a [[Babylonian astronomy|Babylonian astronomer]] who is said to have proved heliocentrism through [[reasoning]] in the 2nd century BC. This may have involved the phenomenon of [[tide]]s,<ref>[[Lucio Russo]], ''Flussi e riflussi'', Feltrinelli, Milano, 2003, ISBN 88-07-10349-4.</ref> 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.<ref>[[Bartel Leendert van der Waerden]] (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy", ''Annals of the New York Academy of Sciences'' '''500''' (1), 525–545 [527].</ref> Alternatively, he may have determined the constants of a [[geometry|geometric]] model for the heliocentric theory and developed methods to compute planetary positions using this model, possibly using early [[trigonometry|trigonometric]] methods that were available in his time, much like Copernicus.<ref>[[Bartel Leendert van der Waerden]] (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy", ''Annals of the New York Academy of Sciences'' '''500''' (1), 525–545 [527-529].</ref> Some have also interpreted the planetary models developed by [[Aryabhata]] (476-550), an [[Indian astronomy|Indian astronomer]],<ref>[[Bartel Leendert van der Waerden|B. L. van der Waerden]] (1970), ''Das heliozentrische System in der griechischen,persischen und indischen Astronomie,'' Naturforschenden Gesellschaft in Zürich, Zürich: Kommissionsverlag Leeman AG. ([[cf.]] Noel Swerdlow (June 1973), "Review: A Lost Monument of Indian Astronomy", ''Isis'' '''64''' (2), p. 239-243.) <br>[[Bartel Leendert van der Waerden|B. L. van der Waerden]] (1987), "The heliocentric system in Greek, Persian, and Indian astronomy", in "From deferent to equant: a volume of studies in the history of science in the ancient and medieval near east in honor of E. S. Kennedy", ''[[New York Academy of Sciences]]'' '''500''', p. 525-546. ([[cf.]] Dennis Duke (2005), "The Equant in India: The Mathematical Basis of Ancient Indian Planetary Models", ''Archive for History of Exact Sciences'' '''59''', p. 563–576.).</ref><ref>Thurston, Hugh (1994), ''Early Astronomy'', Springer-Verlag, New York. ISBN 0-387-94107-X, p. 188: {{quote|"Not only did Aryabhata believe that the earth rotates, but there are glimmerings in his system (and other similar systems) of a possible underlying theory in which the earth (and the planets) orbits the sun, rather than the sun orbiting the earth. The evidence is that the basic planetary periods are relative to the sun."}}</ref><ref>[[Lucio Russo]] (2004), ''The Forgotten Revolution: How Science Was Born in 300 BC and Why It Had To Be Reborn'', [[Springer Science+Business Media|Springer]], Berlin, ISBN 978-3-540-20396-4. ([[cf.]] Dennis Duke (2005), "The Equant in India: The Mathematical Basis of Ancient Indian Planetary Models", ''Archive for History of Exact Sciences'' '''59''', p. 563–576.)</ref> and [[Ja'far ibn Muhammad Abu Ma'shar al-Balkhi|Albumasar]] (787-886), a [[Islamic astronomy|Persian astronomer]], to be heliocentric models.<ref>[[Bartel Leendert van der Waerden]] (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy", ''Annals of the New York Academy of Sciences'' '''500''' (1), 525–545 [534-537].</ref> In the 9th century AD, the [[Islamic physics|Persian physicist]] and [[Islamic astronomy|astronomer]], [[Ja'far Muhammad ibn Mūsā ibn Shākir]], hypothesized that the heavenly bodies and [[celestial spheres]] are subject to the same [[Physical law|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.<ref>{{Harvard reference |last=Saliba |first=George |authorlink=George Saliba |year=1994a |title=Early Arabic Critique of Ptolemaic Cosmology: A Ninth-Century Text on the Motion of the Celestial Spheres |journal=Journal for the History of Astronomy |volume=25 |pages=115-141 [116] }}</ref> He also proposed that there is a [[force]] of [[Gravitation|attraction]] between [[Astronomical object|heavenly bodies]],<ref>{{citation|first=K. A.|last=Waheed|year=1978|title=Islam and The Origins of Modern Science|page=27|publisher=Islamic Publication Ltd., [[Lahore]]}}</ref> vaguely foreshadowing the [[Newton's law of universal gravitation|law of gravity]].<ref>{{Harvard reference |last=Briffault |first=Robert |authorlink=Robert Briffault |year=1938 |title=The Making of Humanity |page=191}}</ref> In the 14th century, [[Ibn al-Shatir]] produced the first model of [[Moon|lunar]] motion which matched physical observations, and which was later used by Copernicus.<ref name=Saliba-2007>[[George Saliba]] (2007), [http://youtube.com/watch?v=GfissgPCgfM Lecture at SOAS, London - Part 4/7] and [http://youtube.com/watch?v=0VMBRAd6YBU Lecture at SOAS, London - Part 5/7]</ref> In the 13th to 15th centuries, [[Nasīr al-Dīn al-Tūsī|Tusi]] and [[Ali Kuşçu]] provided the earliest [[Empirical research|empirical evidence]] for the [[Earth's rotation]], using the phenomena of [[comet]]s to refute Ptolemy's claim that a stationery Earth can be determined through observation. Kuşçu further rejected [[Aristotelian physics]] and [[natural philosophy]], allowing astronomy and physics to become empirical and mathematical instead of philosophical.<ref>{{Harvard reference |last=Ragep |first=F. Jamil |year=2001a |title=Tusi and Copernicus: The Earth's Motion in Context |journal=Science in Context |volume=14 |issue=1-2 |pages=145–163 |publisher=[[Cambridge University Press]] }}</ref><ref>{{Harvard reference |last=Ragep |first=F. Jamil |year=2001b |title=Freeing Astronomy from Philosophy: An Aspect of Islamic Influence on Science |journal=Osiris, 2nd Series |volume=16 |issue=Science in Theistic Contexts: Cognitive Dimensions |pages=49-64 & 66-71 }}</ref> 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 model|geocentric]] dogma of the [[Catholic Church]] of his time, and escaped serious punishment only by maintaining that his astronomy was a work of [[mathematic]]s, 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 Doplers's laws of planetary motion, was the first unification of astronomy and physics. After Isaac Newton published his book, ''[[Philosophiae Naturalis Principia Mathematica]]'', maritime [[navigation]] was transformed. Starting around 1670, the entire world was measured using essentially modern [[latitude]] instruments and the best available [[clock]]s. 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 line]]s 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 element]]s. 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, [[etymology|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.<ref>[http://www.arxiv.org/abs/astro-ph/9711066 Frontiers of Astrophysics: Workshop Summary], H. Falcke, P. L. Biermann</ref> See also: * [[Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure]] * [[Timeline of white dwarfs, neutron stars, and supernovae]] * [[Timeline of black hole physics]] * [[Timeline of gravitational physics and relativity]] ==Becoming an astrophysicist== To become a classic research astronomer (someone who runs a telescope, analyzes data, publishes papers), astrophysicists need to get a Ph.D. degree. Support positions such as telescope operators, observers, and software developers typically require a Bachelor's degree, although some positions may require a Master's degree or higher. [http://www.aas.org/education/publications/careerbrochure.pdf] <ref>http://www.aas.org/education/publications/careerbrochure.pdf</ref> ==Observational astrophysics== [[Image:Pleiades large.jpg|thumb|right|300px|The [[Pleiades (star cluster)|Pleiades]], an [[open cluster]] of stars observed in the [[constellation]] of [[Taurus (constellation)|Taurus]]. ''[[NASA]] photo'']] The majority of astrophysical observations are made using the [[electromagnetic spectrum]]. * [[Radio astronomy]] studies radiation with a [[wavelength]] greater than a few millimeters. [[Radio waves]] are usually emitted by cold objects, including [[interstellar gas]] and dust clouds. The [[cosmic microwave background radiation]] is the [[redshift]]ed light from the [[Big Bang]]. [[Pulsar]]s were first detected at [[microwave]] frequencies. The study of these waves requires very large [[radio telescope]]s. * [[Infrared]] astronomy studies radiation with a wavelength that is too long to be visible but shorter than radio waves. Infrared observations are usually made with telescopes similar to the usual [[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 [[spectroscope]]s are the most common instruments used. The Earth's [[atmosphere]] interferes somewhat with optical observations, so [[adaptive optics]] and [[space telescope]]s are used to obtain the highest possible image quality. In this range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, [[galaxy|galaxies]] and [[nebula]]e. * [[Ultraviolet]], [[X-ray astronomy|X-ray]] and [[gamma ray astronomy]] study very energetic processes such as [[binary pulsar]]s, [[black hole]]s, [[magnetar]]s, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well. There are two possibilities to observe this part of the electromagnetic spectrum—[[space-based telescope]]s and ground-based [[imaging air Cherenkov telescope]]s (IACT). [[Observatory|Observatories]] of the first type are [[RXTE]], the [[Chandra X-ray Observatory]] and the [[Compton Gamma Ray Observatory]]. IACTs are, for example, the [[High Energy Stereoscopic System]] (H.E.S.S.) and the [[MAGIC (telescope)|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 ray]]s 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 [[century|centuries]] or [[millennia]]. On the other hand, radio observations may look at events on a millisecond timescale ([[millisecond pulsar]]s) or combine years of data ([[Rotation-powered pulsar|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. 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 [[Hertzsprung-Russell diagram]], which can be viewed as representing the state of a stellar object, from birth to destruction. The material composition of the astronomical objects can often be examined using: * [[Spectroscopy]] * [[Radio astronomy]] * [[Neutrino astronomy]] (future prospects) ==Theoretical astrophysics== {{Nucleosynthesis}} Theoretical astrophysicists use a wide variety of tools which include [[mathematical model|analytical model]]s (for example, [[polytrope]]s to approximate the behaviors of a [[star]]) and [[computation]]al [[Numerical analysis|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.<ref>H. Roth, ''A Slowly Contracting or Expanding Fluid Sphere and its Stability'', ''Phys. Rev.'' ('''39''', p;525–529, 1932)</ref><ref>A.S. Eddington, ''Internal Constitution of the Stars''</ref> 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 [[Stellar evolution|evolution]]; [[Galaxy formation and evolution|galaxy formation]]; [[large-scale structure]] of [[matter]] in the [[Universe]]; origin of [[cosmic ray]]s; [[general relativity]] and [[physical cosmology]], including [[string theory|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]], and fundamental theories of [[physics]]. A few examples of this process: {| |- ||<!--A--> '''Physical process''' ||<!--B--> '''Experimental tool''' ||<!--C--> '''Theoretical model''' ||<!--D--> '''Explains/predicts''' |- ||<!--A-->[[Gravitation]] ||<!--B-->[[Radio telescope]]s ||<!--C-->[[Nordtvedt effect|Self-gravitating system]] ||<!--D-->Emergence of a [[star system]] |- ||<!--A--> [[Nuclear fusion]] ||<!--B--> [[Spectroscopy]] ||<!--C--> [[Stellar evolution]] ||<!--D--> How the stars shine and how [[nucleosynthesis|metals formed]] |- ||<!--A-->[[The Big Bang]] ||<!--B-->[[Hubble Space Telescope]], [[COBE]] ||<!--C--> [[Expanding universe]] ||<!--D--> [[Age of the Universe]] |- ||<!--A--> [[Quantum fluctuation]]s ||<!--B--> ||<!--C--> [[Cosmic inflation]] ||<!--D--> [[Flatness problem]] |- ||<!--A--> [[Gravitational collapse]] ||<!--B--> [[X-ray astronomy]] ||<!--C--> [[General relativity]] ||<!--D--> [[Black hole]]s at the center of [[Andromeda galaxy]] |- ||<!--A--> [[CNO cycle]] in [[star]]s ||<!--B--> ||<!--C--> ||<!--D--> |- |} [[Dark matter]] and [[dark energy]] are the current leading topics in astrophysics, as their discovery and controversy originated during the study of the galaxies. ==See also== {{portal|Physics}} {{wikibooks|Astrophysics}} * [[List of astronomical observatories|Astronomical observatories]] * [[list of publications in physics#Astrophysics|Important publications in astrophysics]] * [[List of astrophysicists]] * [[Nucleosynthesis]] * [[Particle accelerator]] * [[Astrodynamics]] * [[Astrochemistry]] ==References== {{reflist}} ==External links== * [http://www.intellecttoday.com/ Scientific Discussion: Astrophysics * [http://www.aip.org/history/cosmology/index.htm Cosmic Journey: A History of Scientific Cosmology] from the American Institute of Physics * [http://www.vega.org.uk/video/subseries/16 Prof. Sir Harry Kroto, NL], Astrophysical Chemistry Lecture Series. 8 Freeview Lectures provided by the Vega Science Trust. * [http://home.slac.stanford.edu/ppap.html Stanford Linear Accelerator Center, Stanford, California] * [http://www.iasfbo.inaf.it Institute for Space Astrophysics and Cosmic Physics] * [http://www.journals.uchicago.edu/ApJ/ Astrophysical Journal] * [http://www.aanda.org/ Astronomy and Astrophysics, a European Journal] * [http://www.aas.org/education/publications/careerbrochure.pdf] * [http://master.obspm.fr/ Master of Science in Astronomy and Astrophysics] {{Refimprove|date=November 2007}} {{Astronomy subfields}} [[Category:Astrophysics|*]] [[Category:Applied and interdisciplinary physics]] [[Category:Futurology]] [[af:Astrofisika]] [[ar:فيزياء فلكية]] [[map-bms:Astrofisika]] [[be:Астрафізіка]] [[bs:Astrofizika]] [[bg:Астрофизика]] [[ca:Astrofísica]] [[cv:Астрофизика]] [[cs:Astrofyzika]] [[da:Astrofysik]] [[de:Astrophysik]] [[et:Astrofüüsika]] [[el:Αστροφυσική]] [[es:Astrofísica]] [[eo:Astrofiziko]] [[eu:Astrofisika]] [[fa:اخترفیزیک]] [[fr:Astrophysique]] [[gl:Astrofísica]] [[ko:천체물리학]] [[hr:Astrofizika]] [[id:Astrofisika]] [[is:Stjarneðlisfræði]] [[it:Astrofisica]] [[he:אסטרופיזיקה]] [[ka:ასტროფიზიკა]] [[kn:ಖಭೌತ ಶಾಸ್ತ್ರ]] [[ku:Stêrfîzîk]] [[lv:Astrofizika]] [[lb:Astrophysik]] [[lt:Astrofizika]] [[hu:Asztrofizika]] [[mk:Астрофизика]] [[ms:Astrofizik]] [[nl:Astrofysica]] [[ja:天体物理学]] [[no:Astrofysikk]] [[nov:Astrofisike]] [[pl:Astrofizyka]] [[pt:Astrofísica]] [[ro:Astrofizică]] [[ru:Астрофизика]] [[sq:Astrofizika]] [[simple:Astrophysics]] [[sk:Astrofyzika]] [[sl:Astrofizika]] [[sr:Астрофизика]] [[sh:Astrofizika]] [[fi:Astrofysiikka]] [[sv:Astrofysik]] [[tl:Astropisika]] [[ta:வானியற்பியல்]] [[th:ฟิสิกส์ดาราศาสตร์]] [[vi:Vật lý thiên văn]] [[tr:Astrofizik]] [[uk:Астрофізика]] [[diq:Fizikê Asmêni]] [[zh:天体物理学]]