Array ( [0] => {{Short description|Scientific study of celestial objects}} [1] => {{About|the scientific study of celestial objects}} [2] => {{Distinguish|text=[[astrology]], a pseudoscience}} [3] => {{Good article}} [4] => {{pp-semi-indef}} [5] => {{pp-move}} [6] => {{CS1 config|mode=cs1}} [7] => [[File:Laser Towards Milky Ways Centre.jpg|thumb|upright=1.5|The [[Paranal Observatory]] of [[European Southern Observatory]] shooting a [[laser guide star]] to the [[Galactic Center]]]] [8] => [9] => '''Astronomy''' is a [[natural science]] that studies [[astronomical object|celestial objects]] and the phenomena that occur in the cosmos. It uses [[mathematics]], [[physics]], and [[chemistry]] in order to explain their origin and their overall [[chronology of the Universe|evolution]]. Objects of interest include [[planets]], [[natural satellite|moons]], [[star]]s, [[nebulae]], [[galaxy|galaxies]], [[meteoroid]]s, [[asteroid]]s, and [[comet]]s. Relevant phenomena include [[supernova]] explosions, [[gamma ray burst]]s, [[quasar]]s, [[blazar]]s, [[pulsar]]s, and [[cosmic microwave background radiation]]. More generally, astronomy studies everything that originates beyond [[atmosphere of Earth|Earth's atmosphere]]. [[Cosmology]] is a branch of astronomy that studies the [[universe]] as a whole. [10] => [11] => Astronomy is one of the oldest natural sciences. The early civilizations in [[recorded history]] made methodical observations of the [[night sky]]. These include the [[Egyptian astronomy|Egyptians]], [[Babylonian astronomy|Babylonians]], [[Greek astronomy|Greeks]], [[Indian astronomy|Indians]], [[Chinese astronomy|Chinese]], [[Maya civilization|Maya]], and many ancient [[indigenous peoples of the Americas]]. In the past, astronomy included disciplines as diverse as [[astrometry]], [[celestial navigation]], [[observational astronomy]], and the making of [[calendar]]s. [12] => [13] => Professional astronomy is split into [[observational astronomy|observational]] and [[theoretical astronomy|theoretical]] branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results. [14] => [15] => Astronomy is one of the few sciences in which amateurs play an [[citizen science|active role]]. This is especially true for the discovery and observation of [[transient astronomical event|transient events]]. [[amateur astronomy|Amateur astronomers]] have helped with many important discoveries, such as finding new comets. [16] => [17] => == Etymology == [18] => [[File:SLNSW 479519 16 Observatory SH 198.jpg|thumb|Astronomical Observatory, New South Wales, Australia 1873]] [19] => [[File:Quito Observatory.JPG|thumb|19th-century [[Quito Astronomical Observatory]] is located 12 minutes south of the [[Equator]] in [[Quito]], [[Ecuador]].{{cite web |url=http://oaq.epn.edu.ec/ |title=Inicio |publisher=[[Quito Astronomical Observatory]] |language=es |url-status=live |archive-url=https://web.archive.org/web/20180328112459/https://oaq.epn.edu.ec/ |archive-date=28 March 2018}}]] [20] => ''Astronomy'' (from the [[Ancient Greek|Greek]] [[wikt:ἀστρονομία#Ancient Greek|ἀστρονομία]] from [[wikt:ἄστρον#Ancient Greek|ἄστρον]] ''astron'', "star" and -νομία ''[[wikt:-nomy|-nomia]]'' from [[wikt:νόμος#Ancient Greek|νόμος]] ''nomos'', "law" or "culture") means "law of the stars" (or "culture of the stars" depending on the translation). Astronomy should not be confused with [[astrology]], the belief system which claims that human affairs are correlated with the positions of celestial objects.{{Cite journal |bibcode = 2012JAHH...15...42L|title = 'Astronomy' or 'astrology': A brief history of an apparent confusion|last1 = Losev|first1 = Alexandre|journal = [[Journal of Astronomical History and Heritage]]|volume = 15|issue = 1|pages = 42–46|year = 2012| doi=10.3724/SP.J.1440-2807.2012.01.05 |arxiv = 1006.5209| s2cid=51802196 }} Although the [[Astrology and astronomy|two fields]] share a common origin, they are now entirely distinct.{{cite book|first=Albrecht |last=Unsöld|author2=Baschek, Bodo|others=Translated by Brewer, W.D.|title=The New Cosmos: An Introduction to Astronomy and Astrophysics|date=2001| location=Berlin, New York|publisher=Springer|isbn =978-3-540-67877-9}} [21] => [22] => === Use of terms "astronomy" and "astrophysics" === [23] => "Astronomy" and "[[astrophysics]]" are synonyms.{{cite web|url=http://curious.astro.cornell.edu/question.php?number=30|title= What is the difference between astronomy and astrophysics? |website=Curious About Astronomy |date=January 2002 |last=Scharringhausen|first=B.|access-date=17 November 2016|archive-url=https://web.archive.org/web/20070609102139/http://curious.astro.cornell.edu/question.php?number=30|archive-date=9 June 2007 }}{{cite web|url=http://www.astronomycafe.net/qadir/q449.html|title=Archive of Astronomy Questions and Answers: What is the difference between astronomy and astrophysics?|last=Odenwald|first=Sten |publisher=The Astronomy Cafe|access-date=20 June 2007|archive-url=https://web.archive.org/web/20070708092148/http://www.astronomycafe.net/qadir/q449.html|archive-date=8 July 2007 |url-status=dead }}{{cite web [24] => |title=School of Science-Astronomy and Astrophysics [25] => |website=Penn State Erie [26] => |date=July 18, 2005 [27] => |url=http://www.erie.psu.edu/academic/science/degrees/astronomy/astrophysics.htm [28] => |access-date=20 June 2007 [29] => |archive-url=https://web.archive.org/web/20071101100832/http://www.erie.psu.edu/academic/science/degrees/astronomy/astrophysics.htm [30] => |archive-date=1 November 2007 [31] => }} Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties",{{cite web [32] => |title=astronomy [33] => |work=Merriam-Webster Online [34] => |url=http://www.m-w.com/dictionary/astronomy [35] => |access-date=20 June 2007| archive-url= https://web.archive.org/web/20070617131203/http://www.m-w.com/dictionary/astronomy| archive-date= 17 June 2007 | url-status= live}} while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena".{{cite web [36] => |title=astrophysics [37] => |work=Merriam-Webster Online [38] => |url=http://www.m-w.com/dictionary/astrophysics [39] => |access-date=20 June 2007 [40] => |archive-date=21 September 2012 [41] => |archive-url=https://archive.today/20120921/http://www.m-w.com/dictionary/astrophysics [42] => |url-status=live [43] => }} In some cases, as in the introduction of the introductory textbook ''The Physical Universe'' by [[Frank Shu]], "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject.{{cite book [44] => |first = F.H. [45] => |last = Shu [46] => |title = The Physical Universe [47] => |publisher = University Science Books [48] => |date = 1983 [49] => |location = Mill Valley, California [50] => |isbn = 978-0-935702-05-7 [51] => |url-access = registration [52] => |url = https://archive.org/details/physicaluniverse00shuf [53] => }} However, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Some fields, such as [[astrometry]], are purely astronomy rather than also astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics", partly depending on whether the department is historically affiliated with a physics department, and many professional [[astronomer]]s have physics rather than astronomy degrees. Some titles of the leading scientific journals in this field include ''[[The Astronomical Journal]]'', ''[[The Astrophysical Journal]]'', and ''[[Astronomy & Astrophysics]]''. [54] => [55] => == History == [56] => {{Main|History of astronomy}} [57] => {{For timeline}} [58] => {{Further|Archaeoastronomy|List of astronomers}} [59] => [[File:Planisphæri cœleste.jpg|thumb|A celestial map from the 17th century, by the Dutch cartographer [[Frederik de Wit]].]] [60] => [61] => === Ancient times === [62] => [63] => In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye. In some locations, early cultures assembled massive artifacts that may have had some astronomical purpose. In addition to their ceremonial uses, these [[Observatory|observatories]] could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year.{{cite book | first=George | last=Forbes | title=History of Astronomy | publisher=Plain Label Books | location=London | date=1909 | isbn=978-1-60303-159-2 | url=http://www.gutenberg.org/ebooks/8172 | access-date=7 April 2019 | archive-date=28 August 2018 | archive-url=https://web.archive.org/web/20180828185512/http://www.gutenberg.org/ebooks/8172 | url-status=live }} [64] => [65] => Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye. As civilizations developed, most notably in [[Egyptian astronomy|Egypt]], [[Babylonian astronomy|Mesopotamia]], [[Greek astronomy|Greece]], [[Persian astronomy|Persia]], [[Indian astronomy|India]], [[Chinese astronomy|China]], and [[Maya civilization|Central America]], astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as [[astrometry]]. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon and the Earth in the Universe were explored philosophically. The Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the [[geocentric model]] of the Universe, or the [[Ptolemaic system]], named after [[Ptolemy]].{{cite book|last=DeWitt|first=Richard|title=Worldviews: An Introduction to the History and Philosophy of Science|date=2010|publisher=Wiley|location=Chichester, England|isbn=978-1-4051-9563-8|page=113|chapter=The Ptolemaic System}} [66] => [[File:Suryaprajnapati Sutra.jpg|thumb|The Suryaprajnaptisūtra, a 6th-century BC astronomy text of [[Jains]] at The Schoyen Collection, London. Above: its manuscript from {{circa|1500}} AD.[http://www.schoyencollection.com/23-religions/living-religions/23-17-jainism/astronomy/ms-5297 SuryaprajnaptiSūtra] {{Webarchive|url=https://web.archive.org/web/20170615024618/http://www.schoyencollection.com/23-religions/living-religions/23-17-jainism/astronomy/ms-5297 |date=15 June 2017 }}, The Schoyen Collection, London/Oslo]] [67] => A particularly important early development was the beginning of mathematical and scientific astronomy, which began among [[Babylonian astronomy|the Babylonians]], who laid the foundations for the later astronomical traditions that developed in many other civilizations.{{cite journal|title=Scientific Astronomy in Antiquity|author=Aaboe, A. |journal=[[Philosophical Transactions of the Royal Society]]|volume=276|issue=1257|date=1974|pages=21–42|jstor=74272|doi=10.1098/rsta.1974.0007|bibcode = 1974RSPTA.276...21A |s2cid=122508567 }} The [[Babylonian astronomy|Babylonians]] discovered that [[lunar eclipses]] recurred in a repeating cycle known as a [[Saros cycle|saros]].{{cite web|url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |title=Eclipses and the Saros |publisher=NASA |access-date=28 October 2007 |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |archive-date=30 October 2007 }} [68] => [[File:AiKhanoumSunDial.jpg|thumb|Greek equatorial [[sundial]], [[Alexandria on the Oxus]], present-day Afghanistan 3rd–2nd century BC.]] [69] => [70] => Following the Babylonians, significant advances in astronomy were made in [[ancient Greece]] and the [[Hellenistic civilization|Hellenistic]] world. [[Greek astronomy]] is characterized from the start by seeking a rational, physical explanation for celestial phenomena.{{Cite book| last = Krafft| first = Fritz| date = 2009| contribution = Astronomy| editor-last = Cancik| editor-first = Hubert| editor2-last = Schneider| editor2-first = Helmuth| title = Brill's New Pauly| title-link = Brill's New Pauly}} In the 3rd century BC, [[Aristarchus of Samos]] estimated the [[Aristarchus On the Sizes and Distances|size and distance of the Moon and Sun]], and he proposed a model of the [[Solar System]] where the Earth and planets rotated around the Sun, now called the [[heliocentrism|heliocentric]] model.{{cite journal | title = Aristarchus's On the Sizes and Distances of the Sun and the Moon: Greek and Arabic Texts | journal = Archive for History of Exact Sciences | date = May 2007 | first1 = J.L. | last1 = Berrgren |first2= Nathan |last2= Sidoli | volume = 61 | issue = 3 | pages = 213–54 | doi = 10.1007/s00407-006-0118-4| s2cid = 121872685 }} In the 2nd century BC, [[Hipparchus]] discovered [[precession]], calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the [[astrolabe]].{{cite web|url=http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Hipparchus.html|title=Hipparchus of Rhodes|publisher=School of Mathematics and Statistics, [[University of St Andrews]], Scotland|access-date=28 October 2007|archive-url=https://web.archive.org/web/20071023062202/http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Hipparchus.html|archive-date=23 October 2007 |url-status=live}} Hipparchus also created a comprehensive catalog of 1020 stars, and most of the [[constellation]]s of the northern hemisphere derive from Greek astronomy.{{cite book|last=Thurston|first=H.|title=Early Astronomy|url=https://books.google.com/books?id=rNpHjqxQQ9oC&pg=PA2|year=1996|publisher=Springer Science & Business Media|isbn=978-0-387-94822-5|page=2|access-date=20 June 2015|archive-date=3 February 2021|archive-url=https://web.archive.org/web/20210203012120/https://books.google.com/books?id=rNpHjqxQQ9oC&pg=PA2|url-status=live}} The [[Antikythera mechanism]] ({{circa|150}}–80 BC) was an early [[analog computer]] designed to calculate the location of the [[Sun]], [[Moon]], and [[planets]] for a given date. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical [[astronomical clock]]s appeared in Europe.{{cite journal|last1=Marchant|first1=Jo|title=In search of lost time|journal=Nature|volume=444|issue=7119|pages=534–38|date=2006|pmid=17136067|doi=10.1038/444534a|bibcode = 2006Natur.444..534M |doi-access=free}} [71] => [72] => === Middle Ages === [73] => [74] => Medieval Europe housed a number of important astronomers. [[Richard of Wallingford]] (1292–1336) made major contributions to astronomy and [[horology]], including the invention of the first astronomical clock, the [[Rectangulus]] which allowed for the measurement of angles between planets and other astronomical bodies, as well as an [[equatorium]] called the ''Albion'' which could be used for astronomical calculations such as [[moon|lunar]], [[sun|solar]] and [[planet]]ary [[longitude]]s and could predict [[eclipse]]s. [[Nicole Oresme]] (1320–1382) and [[Jean Buridan]] (1300–1361) first discussed evidence for the rotation of the Earth, furthermore, Buridan also developed the theory of impetus (predecessor of the modern scientific theory of [[inertia]]) which was able to show planets were capable of motion without the intervention of angels.Hannam, James. ''God's philosophers: how the medieval world laid the foundations of modern science''. Icon Books Ltd, 2009, 180 [[Georg von Peuerbach]] (1423–1461) and [[Regiomontanus]] (1436–1476) helped make astronomical progress instrumental to Copernicus's development of the heliocentric model decades later. [75] => [76] => [[Astronomy in medieval Islam|Astronomy flourished in the Islamic world]] and other parts of the world. This led to the emergence of the first astronomical [[Observatory|observatories]] in the [[Muslim world]] by the early 9th century.{{Cite journal |last=Kennedy |first=Edward S. |date=1962 |title=Review: ''The Observatory in Islam and Its Place in the General History of the Observatory'' by Aydin Sayili |journal=[[Isis (journal)|Isis]] |volume=53 |issue=2 |pages=237–39 |doi=10.1086/349558 }}{{Cite journal|last=Micheau|first=Françoise|editor-last=Rashed|editor-first=Roshdi|editor2-last=Morelon|editor2-first=Régis|title=The Scientific Institutions in the Medieval Near East|journal=Encyclopedia of the History of Arabic Science|volume=3|pages=992–93}}{{cite book |last=Nas |first=Peter J|title=Urban Symbolism|date=1993 |publisher=Brill Academic Publishers |isbn=978-90-04-09855-8|page=350}} In 964, the [[Andromeda Galaxy]], the largest [[galaxy]] in the [[Local Group]], was described by the Persian Muslim astronomer [[Abd al-Rahman al-Sufi]] in his ''[[Book of Fixed Stars]]''.{{cite book |last1= Kepple |first1= George Robert |first2=Glen W. |last2=Sanner |title= The Night Sky Observer's Guide |volume= 1 |publisher= Willmann-Bell, Inc. |date= 1998 |isbn= 978-0-943396-58-3 |page=18}} The [[SN 1006]] [[supernova]], the brightest [[apparent magnitude]] stellar event in recorded history, was observed by the Egyptian Arabic astronomer [[Ali ibn Ridwan]] and [[Chinese astronomy|Chinese astronomers]] in 1006. Iranian scholar [[Al-Biruni]] observed that, contrary to [[Ptolemy]], the Sun's [[apogee]] (highest point in the heavens) was mobile, not fixed.{{cite news |last1=Covington |first1=Richard |title=Rediscovering Arabic Science |url=http://archive.aramcoworld.com/issue/200703/rediscovering.arabic.science.htm |access-date=6 March 2023 |work=[[Aramco World]] |issue=3 |volume=58 |date=2007 |archive-date=1 March 2021 |archive-url=https://web.archive.org/web/20210301151438/https://archive.aramcoworld.com/issue/200703/rediscovering.arabic.science.htm |url-status=live }} Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science include [[Al-Battani]], [[Thebit]], [[Abd al-Rahman al-Sufi]], [[Abu Rayhan Biruni|Biruni]], [[Abū Ishāq Ibrāhīm al-Zarqālī]], [[Al-Birjandi]], and the astronomers of the [[Maragheh observatory|Maragheh]] and [[Ulugh Beg Observatory|Samarkand]] observatories. Astronomers during that time introduced many [[List of Arabic star names|Arabic names now used for individual stars]].{{cite book|first=Arthur|last=Berry|title=A Short History of Astronomy From Earliest Times Through the 19th Century|publisher=Dover Publications, Inc.|location=New York|date=1961|isbn=978-0-486-20210-5|url-access=registration|url=https://archive.org/details/shorthistoryofas0000berr}}{{cite book|editor=Hoskin, Michael|title=The Cambridge Concise History of Astronomy|publisher=Cambridge University Press|date=1999|isbn = 978-0-521-57600-0}} [77] => [78] => It is also believed that the ruins at [[Great Zimbabwe]] and [[Timbuktu]]{{cite book|url=https://archive.org/details/royalkingdomsofg00patr|url-access=registration|page=[https://archive.org/details/royalkingdomsofg00patr/page/103 103]|title= The royal kingdoms of Ghana, Mali, and Songhay: life in medieval Africa|first=Pat|last= McKissack|author2=McKissack, Frederick|date=1995|publisher=H. Holt|isbn=978-0-8050-4259-7}} may have housed astronomical observatories.{{cite journal|url=https://www.newscientist.com/article/dn3137-eclipse-brings-claim-of-medieval-african-observatory.html|title=Eclipse brings claim of medieval African observatory|date=2002|journal=New Scientist|access-date=3 February 2010|last=Clark|first=Stuart|author2=Carrington, Damian|archive-date=30 April 2015|archive-url=https://web.archive.org/web/20150430173144/http://www.newscientist.com/article/dn3137-eclipse-brings-claim-of-medieval-african-observatory.html|url-status=live}} In [[Post-classical]] [[West Africa]], Astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens as well as precise diagrams of orbits of the other planets based on complex mathematical calculations. [[Songhai Empire|Songhai]] historian [[Mahmud Kati]] documented a [[meteor shower]] in August 1583.{{Cite book|last=Hammer|first=Joshua|title=The Bad-Ass Librarians of Timbuktu And Their Race to Save the World's Most Precious Manuscripts|publisher=Simon & Schuster|year=2016|isbn=978-1-4767-7743-6|location=New York|pages=26–27}}{{cite book|url=https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182|title=African Cultural Astronomy|first=Jarita C.|last=Holbrook|author2=Medupe, R. Thebe|author3=Urama, Johnson O.|publisher=Springer|date=2008|isbn=978-1-4020-6638-2|access-date=19 October 2020|archive-date=17 August 2021|archive-url=https://web.archive.org/web/20210817020340/https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182|url-status=live}} [79] => Europeans had previously believed that there had been no astronomical observation in [[sub-Saharan Africa]] during the pre-colonial Middle Ages, but modern discoveries show otherwise.{{cite web|url=http://www.scienceinafrica.co.za/2003/november/cosmic.htm |title=Cosmic Africa explores Africa's astronomy |access-date=3 February 2002 |publisher=Science in Africa |archive-url=https://web.archive.org/web/20031203055223/http://www.scienceinafrica.co.za/2003/november/cosmic.htm |archive-date=3 December 2003 }}{{cite book|url=https://books.google.com/books?id=4DJpDW6IAukC&pg=PA180|title=African Cultural Astronomy|first=Jarita C.|last=Holbrook|author2=Medupe, R. Thebe|author3=Urama, Johnson O.|publisher=Springer|date=2008|isbn=978-1-4020-6638-2|access-date=26 August 2020|archive-date=26 August 2016|archive-url=https://web.archive.org/web/20160826084847/https://books.google.com/books?id=4DJpDW6IAukC&pg=PA180|url-status=live}}{{cite web|url=http://royalsociety.org/news.asp?year=&id=4117 |title=Africans studied astronomy in medieval times|date=30 January 2006|publisher=The Royal Society|access-date=3 February 2010 |archive-url = https://web.archive.org/web/20080609112829/http://royalsociety.org/news.asp?year=&id=4117 |archive-date = 9 June 2008}}Stenger, Richard {{cite news|url=http://articles.cnn.com/2002-12-05/tech/zimbabwe.observatory_1_supernova-forecast-eclipses-star |title=Star sheds light on African 'Stonehenge' |work=CNN |date=5 December 2002 |archive-url=https://web.archive.org/web/20110512162930/http://articles.cnn.com/2002-12-05/tech/zimbabwe.observatory_1_supernova-forecast-eclipses-star?_s=PM%3ATECH |archive-date=12 May 2011 }}. CNN. 5 December 2002. Retrieved on 30 December 2011. [80] => [81] => For over six centuries (from the recovery of ancient learning during the late Middle Ages into the Enlightenment), the [[Roman Catholic Church]] gave more financial and social support to the study of astronomy than probably all other institutions. Among the Church's motives was finding the [[Date of Easter|date for Easter]].J.L. Heilbron, ''The Sun in the Church: Cathedrals as Solar Observatories'' (1999), p. 3 [82] => [83] => === Scientific revolution === [84] => [[File:Galileo moon phases.jpg|thumb|[[Galileo]]'s sketches and observations of the [[Moon]] revealed that the surface was mountainous.]] [85] => [[File:Medieval Astronomy (f.4v).jpg|thumb|An astronomical chart from an early scientific manuscript, {{Circa|1000}}.]] [86] => During the [[Renaissance]], [[Nicolaus Copernicus]] proposed a heliocentric model of the solar system. His work was defended by [[Galileo Galilei]] and expanded upon by [[Johannes Kepler]]. Kepler was the first to devise a system that correctly described the details of the motion of the planets around the Sun. However, Kepler did not succeed in formulating a theory behind the laws he wrote down.{{harvnb|Forbes|1909|pp=49–58}} It was [[Isaac Newton]], with his invention of [[celestial dynamics]] and his [[gravity|law of gravitation]], who finally explained the motions of the planets. Newton also developed the [[reflecting telescope]].{{harvnb|Forbes|1909|pp=58–64}} [87] => [88] => Improvements in the size and quality of the telescope led to further discoveries. The English astronomer [[John Flamsteed]] catalogued over 3000 stars,Chambers, Robert (1864) ''[[Chambers Book of Days]]'' More extensive star catalogues were produced by [[Nicolas Louis de Lacaille]]. The astronomer [[William Herschel]] made a detailed catalog of nebulosity and clusters, and in 1781 discovered the planet [[Uranus]], the first new planet found.{{harvnb|Forbes|1909|pp=79–81}} [89] => [90] => During the 18–19th centuries, the study of the [[three-body problem]] by [[Leonhard Euler]], [[Alexis Claude Clairaut]], and [[Jean le Rond d'Alembert]] led to more accurate predictions about the motions of the Moon and planets. This work was further refined by [[Joseph-Louis Lagrange]] and [[Pierre Simon Laplace]], allowing the masses of the planets and moons to be estimated from their perturbations.{{harvnb|Forbes|1909|pp=74–76}} [91] => [92] => Significant advances in astronomy came about with the introduction of new technology, including the [[spectroscope]] and [[Astrophotography|photography]]. [[Joseph von Fraunhofer]] discovered about 600 bands in the spectrum of the Sun in 1814–15, which, in 1859, [[Gustav Kirchhoff]] ascribed to the presence of different elements. Stars were proven to be similar to the Earth's own Sun, but with a wide range of [[temperature]]s, [[mass]]es, and sizes. [93] => [94] => The existence of the Earth's galaxy, the [[Milky Way]], as its own group of stars was only proved in the 20th century, along with the existence of "external" galaxies. The observed recession of those galaxies led to the discovery of the expansion of the [[Universe]].{{cite book|author=Belkora, Leila|title=Minding the heavens: the story of our discovery of the Milky Way|isbn=978-0-7503-0730-7|url=https://books.google.com/books?id=qBM-wez94WwC|publisher=[[CRC Press]]|date=2003|pages=1–14|access-date=26 August 2020|archive-date=27 October 2020|archive-url=https://web.archive.org/web/20201027093857/https://books.google.com/books?id=qBM-wez94WwC|url-status=live}} Theoretical astronomy led to speculations on the existence of objects such as [[black hole]]s and [[neutron star]]s, which have been used to explain such observed phenomena as [[quasar]]s, [[pulsar]]s, [[blazar]]s, and [[radio galaxy|radio galaxies]]. [[Physical cosmology]] made huge advances during the 20th century. In the early 1900s the model of the [[Big Bang]] theory was formulated, heavily evidenced by [[cosmic microwave background radiation]], [[Hubble's law]], and the [[Big Bang nucleosynthesis|cosmological abundances of elements]]. [[Space telescope]]s have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.{{cite book | chapter=Beating the atmosphere | first=Ian S. | last=McLean | title=Electronic Imaging in Astronomy | series=Springer Praxis Books | date=2008 | isbn=978-3-540-76582-0 | pages=39–75 | publisher=Springer | location=Berlin, Heidelberg | doi=10.1007/978-3-540-76583-7_2 }} In February 2016, it was revealed that the [[LIGO]] project had [[first observation of gravitational waves|detected evidence]] of [[gravitational waves]] in the previous September.{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News |url=http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |date=11 February 2016 |last1=Castelvecchi |first1=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361 |s2cid=182916902 |access-date=11 February 2016 |archive-date=12 February 2016 |archive-url=https://web.archive.org/web/20160212082216/http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |url-status=live }}{{cite journal |title=Observation of Gravitational Waves from a Binary Black Hole Merger| author=B.P. Abbott |collaboration=LIGO Scientific Collaboration and Virgo Collaboration| journal=Physical Review Letters| year=2016| volume=116|issue=6| pages=061102| doi=10.1103/PhysRevLett.116.061102| pmid=26918975| bibcode=2016PhRvL.116f1102A|arxiv = 1602.03837 | s2cid=124959784}} [95] => [96] => == Observational astronomy == [97] => {{Main|Observational astronomy}} [98] => [[File:Openstax Astronomy EM spectrum and atmosphere.jpg|thumb|upright=1.6|Overview of types of observational astronomy by observed wavelengths and their observability.]] [99] => The main source of information about [[celestial body|celestial bodies]] and other objects is [[visible light]], or more generally [[electromagnetic radiation]].{{cite web|url=http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html|title=Electromagnetic Spectrum|publisher=NASA|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060905131651/http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html|archive-date=5 September 2006 }} Observational astronomy may be categorized according to the corresponding region of the [[electromagnetic spectrum]] on which the observations are made. Some parts of the spectrum can be observed from the Earth's surface, while other parts are only observable from either high altitudes or outside the Earth's atmosphere. Specific information on these subfields is given below. [100] => [101] => ===Radio astronomy=== [102] => [[File:USA.NM.VeryLargeArray.02.jpg|thumb|The [[Very Large Array]] in [[New Mexico]], an example of a [[radio telescope]]]] [103] => {{Main|Radio astronomy}} [104] => Radio astronomy uses radiation with [[wavelength]]s greater than approximately one millimeter, outside the visible range.{{cite book [105] => |editor=Cox, A.N. [106] => |title=Allen's Astrophysical Quantities [107] => |date=2000 [108] => |url=https://books.google.com/books?id=w8PK2XFLLH8C&pg=PA124 [109] => |publisher=Springer-Verlag [110] => |page=124 [111] => |location=New York [112] => |isbn=978-0-387-98746-0 [113] => |access-date=26 August 2020 [114] => |archive-date=19 November 2020 [115] => |archive-url=https://web.archive.org/web/20201119200822/https://books.google.com/books?id=w8PK2XFLLH8C&pg=PA124 [116] => |url-status=live [117] => }} Radio astronomy is different from most other forms of observational astronomy in that the observed [[radio wave]]s can be treated as [[wave]]s rather than as discrete [[photon]]s. Hence, it is relatively easier to measure both the [[amplitude]] and [[Phase (waves)|phase]] of radio waves, whereas this is not as easily done at shorter wavelengths. [118] => [119] => Although some [[radio wave]]s are emitted directly by astronomical objects, a product of [[black-body radiation|thermal emission]], most of the radio emission that is observed is the result of [[synchrotron radiation]], which is produced when [[electron]]s orbit [[magnetic field]]s. Additionally, a number of [[spectral line]]s produced by [[interstellar gas]], notably the [[hydrogen]] spectral line at 21 cm, are observable at radio wavelengths. [120] => [121] => A wide variety of other objects are observable at radio wavelengths, including [[supernova]]e, interstellar gas, [[pulsar]]s, and [[active galactic nuclei]]. [122] => [123] => === Infrared astronomy === [124] => [[File:In Search of Space.jpg|thumb|[[Atacama Large Millimeter Array|ALMA]] Observatory is one of the highest observatory sites on Earth. Atacama, Chile.{{cite news|title=In Search of Space|url=http://www.eso.org/public/images/potw1431a/|access-date=5 August 2014|work=Picture of the Week|agency=European Southern Observatory|archive-date=13 August 2020|archive-url=https://web.archive.org/web/20200813090738/https://www.eso.org/public/images/potw1431a/|url-status=live}}]] [125] => {{Main|Infrared astronomy}} [126] => Infrared astronomy is founded on the detection and analysis of [[infrared]] radiation, wavelengths longer than red light and outside the range of our vision. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, [[circumstellar disk]]s or nebulae whose light is blocked by dust. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded in [[molecular cloud]]s and the cores of galaxies. Observations from the [[Wide-field Infrared Survey Explorer]] (WISE) have been particularly effective at unveiling numerous galactic [[protostar]]s and their host [[star clusters]].{{cite web|url=http://wise.ssl.berkeley.edu/|title=Wide-field Infrared Survey Explorer Mission|date=30 September 2014|publisher=[[NASA]] [[University of California, Berkeley]]|access-date=17 November 2016|archive-url=https://web.archive.org/web/20100112144939/http://wise.ssl.berkeley.edu/|archive-date=12 January 2010}}{{Cite journal |bibcode = 2013Ap&SS.344..175M|title = Discovering protostars and their host clusters via WISE|last1 = Majaess|first1 = D.|journal = Astrophysics and Space Science|volume = 344|issue = 1|pages = 175–186|year = 2013|arxiv = 1211.4032|doi = 10.1007/s10509-012-1308-y|s2cid = 118455708}} [127] => With the exception of infrared [[wavelengths]] close to visible light, such radiation is heavily absorbed by the atmosphere, or masked, as the atmosphere itself produces significant infrared emission. Consequently, infrared observatories have to be located in high, dry places on Earth or in space.{{cite news [128] => |author=Staff [129] => |date=11 September 2003 [130] => |title=Why infrared astronomy is a hot topic [131] => |publisher=ESA [132] => |url=http://www.esa.int/esaCP/SEMX9PZO4HD_FeatureWeek_0.html [133] => |access-date=11 August 2008 [134] => |archive-date=30 July 2012 [135] => |archive-url=https://archive.today/20120730/http://www.esa.int/esaCP/SEMX9PZO4HD_FeatureWeek_0.html [136] => |url-status=live [137] => }} Some molecules radiate strongly in the infrared. This allows the study of the chemistry of space; more specifically it can detect water in comets.{{cite news|url=http://www.ipac.caltech.edu/Outreach/Edu/Spectra/irspec.html|title=Infrared Spectroscopy – An Overview|publisher=[[NASA]] [[California Institute of Technology]]|access-date=11 August 2008|archive-url=https://web.archive.org/web/20081005031543/http://www.ipac.caltech.edu/Outreach/Edu/Spectra/irspec.html|archive-date=5 October 2008}} [138] => [139] => === Optical astronomy === [140] => [[File:The Keck Subaru and Infrared obervatories.JPG|thumb|The [[Subaru Telescope]] (left) and [[Keck Observatory]] (center) on [[Mauna Kea]], both examples of an observatory that operates at near-infrared and visible wavelengths. The [[NASA Infrared Telescope Facility]] (right) is an example of a telescope that operates only at near-infrared wavelengths.]] [141] => {{Main|Optical astronomy}} [142] => Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy.{{cite book [143] => |author=Moore, P. [144] => |title=Philip's Atlas of the Universe [145] => |date=1997 [146] => |publisher=George Philis Limited [147] => |location=Great Britain [148] => |isbn=978-0-540-07465-5}} Images of observations were originally drawn by hand. In the late 19th century and most of the 20th century, images were made using photographic equipment. Modern images are made using digital detectors, particularly using [[charge-coupled device]]s (CCDs) and recorded on modern medium. Although visible light itself extends from approximately 4000 [[Ångstrom|Å]] to 7000 Å (400 [[nanometre|nm]] to 700 nm), that same equipment can be used to observe some [[near-ultraviolet]] and [[near-infrared]] radiation. [149] => [150] => === Ultraviolet astronomy === [151] => {{Main|Ultraviolet astronomy}} [152] => [153] => Ultraviolet astronomy employs [[ultraviolet]] wavelengths between approximately 100 and 3200 Å (10 to 320 nm). Light at those wavelengths is absorbed by the Earth's atmosphere, requiring observations at these wavelengths to be performed from the upper atmosphere or from space. Ultraviolet astronomy is best suited to the study of thermal radiation and spectral emission lines from hot blue [[star]]s ([[OB star]]s) that are very bright in this wave band. This includes the blue stars in other galaxies, which have been the targets of several ultraviolet surveys. Other objects commonly observed in ultraviolet light include [[planetary nebula]]e, [[supernova remnant]]s, and active galactic nuclei. However, as ultraviolet light is easily absorbed by [[interstellar dust]], an adjustment of ultraviolet measurements is necessary. [154] => [155] => === X-ray astronomy === [156] => {{Main|X-ray astronomy}} [157] => [[File:B30727.jpg|thumb|X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe]] [158] => X-ray astronomy uses [[X-radiation|X-ray wavelengths]]. Typically, X-ray radiation is produced by [[synchrotron emission]] (the result of electrons orbiting magnetic field lines), [[bremsstrahlung radiation|thermal emission from thin gases]] above 107 (10 million) [[kelvin]]s, and [[blackbody radiation|thermal emission from thick gases]] above 107 Kelvin. Since X-rays are absorbed by the [[Earth's atmosphere]], all X-ray observations must be performed from [[high-altitude balloon]]s, [[rocket]]s, or [[X-ray astronomy satellite]]s. Notable [[Astrophysical X-ray source|X-ray sources]] include [[X-ray binaries]], [[pulsar]]s, [[supernova remnant]]s, [[elliptical galaxies]], [[clusters of galaxies]], and [[active galactic nuclei]]. [159] => [160] => === Gamma-ray astronomy === [161] => {{Main|Gamma ray astronomy}} [162] => Gamma ray astronomy observes astronomical objects at the shortest wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as the [[Compton Gamma Ray Observatory]] or by specialized telescopes called [[atmospheric Cherenkov telescope]]s. The Cherenkov telescopes do not detect the gamma rays directly but instead detect the flashes of visible light produced when gamma rays are absorbed by the Earth's atmosphere.{{cite web|url=http://www.pparc.ac.uk/frontiers/latest/feature.asp?article=14F1&style=feature|title=The electromagnetic spectrum|last=Penston|first=Margaret J.|date=14 August 2002|publisher=Particle Physics and Astronomy Research Council|archive-url=https://archive.today/20120908014227/http://www.pparc.ac.uk/frontiers/latest/feature.asp?article=14F1&style=feature|archive-date=8 September 2012|access-date=17 November 2016}} [163] => [164] => Most [[Gamma ray|gamma-ray]] emitting sources are actually [[gamma-ray burst]]s, objects which only produce gamma radiation for a few milliseconds to thousands of seconds before fading away. Only 10% of gamma-ray sources are non-transient sources. These steady gamma-ray emitters include pulsars, [[neutron star]]s, and [[black hole]] candidates such as active galactic nuclei. [165] => [166] => === Fields not based on the electromagnetic spectrum === [167] => In addition to electromagnetic radiation, a few other events originating from great distances may be observed from the Earth. [168] => [169] => In [[neutrino astronomy]], astronomers use heavily shielded [[Neutrino observatory|underground facilities]] such as [[SAGE (ruSsian American Gallium Experiment)|SAGE]], [[GALLEX]], and [[Kamioka Observatory|Kamioka II/III]] for the detection of [[neutrino]]s. The vast majority of the neutrinos streaming through the Earth originate from the [[Sun]], but 24 neutrinos were also detected from [[supernova 1987A]]. [[Cosmic ray]]s, which consist of very high energy particles (atomic nuclei) that can decay or be absorbed when they enter the Earth's atmosphere, result in a cascade of secondary particles which can be detected by current observatories.{{cite book [170] => |first=Thomas K.|last=Gaisser|date=1990 [171] => |title=Cosmic Rays and Particle Physics|url=https://archive.org/details/cosmicrayspartic0000gais|url-access=registration|pages=[https://archive.org/details/cosmicrayspartic0000gais/page/1 1–2] [172] => |publisher=Cambridge University Press|isbn=978-0-521-33931-5}} Some future [[neutrino detector]]s may also be sensitive to the particles produced when cosmic rays hit the Earth's atmosphere. [173] => [174] => [[Gravitational-wave astronomy]] is an emerging field of astronomy that employs [[gravitational-wave detector]]s to collect observational data about distant massive objects. A few observatories have been constructed, such as the ''Laser Interferometer Gravitational Observatory'' [[LIGO]]. LIGO made its [[First observation of gravitational waves|first detection]] on 14 September 2015, observing gravitational waves from a [[binary black hole]].{{cite journal |collaboration=LIGO Scientific Collaboration and Virgo Collaboration |last1=Abbott |first1=Benjamin P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |journal=[[Physical Review Letters]] |volume=116 |issue=6 |pages=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |arxiv=1602.03837 |bibcode=2016PhRvL.116f1102A |pmid=26918975 |s2cid=124959784 }} A second [[gravitational wave]] was detected on 26 December 2015 and additional observations should continue but [[gravitational wave]]s require extremely sensitive instruments.{{cite web |url=http://www.europhysicsnews.org/index.php?option=article&access=standard&Itemid=129&url=/articles/epn/abs/2003/02/epn03208/epn03208.html |title=Opening new windows in observing the Universe |last1=Tammann |first1=Gustav-Andreas |author-link=Gustav Andreas Tammann |first2=Friedrich-Karl |last2=Thielemann |author-link2=Friedrich-Karl Thielemann |first3=Dirk |last3=Trautmann |date=2003 |publisher=Europhysics News |archive-url=https://archive.today/20120906192257/http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/abs/2003/02/epn03208/epn03208.html |archive-date=6 September 2012 |access-date=17 November 2016 }}{{Cite journal |author1=LIGO Scientific Collaboration and Virgo Collaboration |last2=Abbott |first2=B. P. |last3=Abbott |first3=R. |last4=Abbott |first4=T. D.|last5=Abernathy |first5=M. R. |last6=Acernese |first6=F. |last7=Ackley |first7=K. |last8=Adams |first8=C. |last9=Adams |first9=T. |date=15 June 2016 |title=GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence |journal=Physical Review Letters |volume=116 |issue=24 |pages=241103 |doi=10.1103/PhysRevLett.116.241103 |pmid=27367379 |arxiv=1606.04855 |bibcode=2016PhRvL.116x1103A |s2cid=118651851 }} [175] => [176] => The combination of observations made using electromagnetic radiation, neutrinos or gravitational waves and other complementary information, is known as [[multi-messenger astronomy]].{{cite web|title=Planning for a bright tomorrow: Prospects for gravitational-wave astronomy with Advanced LIGO and Advanced Virgo|url=http://www.ligo.org/science/Publication-ObservingScenario/index.php|publisher=[[LIGO Scientific Collaboration]]|access-date=31 December 2015|archive-date=23 April 2016|archive-url=https://web.archive.org/web/20160423031110/http://www.ligo.org/science/Publication-ObservingScenario/index.php|url-status=live}}{{cite book |title=Neutrinos in Particle Physics, Astronomy and Cosmology |first1=Zhizhong |last1=Xing |first2=Shun |last2=Zhou |publisher=Springer |date=2011 |isbn=978-3-642-17560-2 |page=313 |url=https://books.google.com/books?id=6QXqlCHLjJkC&pg=PA313 |access-date=20 June 2015 |archive-date=3 February 2021 |archive-url=https://web.archive.org/web/20210203012300/https://books.google.com/books?id=6QXqlCHLjJkC&pg=PA313 |url-status=live }} [177] => [178] => === Astrometry and celestial mechanics === [179] => {{Main|Astrometry|Celestial mechanics}} [180] => [[File:EmissionNebula NGC6357.jpg|thumb|Star cluster [[Pismis 24]] with a nebula]] [181] => One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects. Historically, accurate knowledge of the positions of the Sun, Moon, planets and stars has been essential in [[celestial navigation]] (the use of celestial objects to guide navigation) and in the making of [[calendar]]s.{{Cite book |last=Fraknoi |first=Andrew |url=https://openstax.org/details/books/astronomy-2e |title=Astronomy 2e |date=2022 |display-authors=etal |publisher=OpenStax |isbn=978-1-951693-50-3 |edition=2e |oclc=1322188620 |access-date=16 March 2023 |archive-date=23 February 2023 |archive-url=https://web.archive.org/web/20230223211041/https://openstax.org/details/books/astronomy-2e |url-status=live }}{{rp|39}} [182] => [183] => Careful measurement of the positions of the planets has led to a solid understanding of gravitational [[Perturbation theory|perturbations]], and an ability to determine past and future positions of the planets with great accuracy, a field known as [[celestial mechanics]]. More recently the tracking of [[near-Earth object]]s will allow for predictions of close encounters or potential collisions of the Earth with those objects.{{cite web|last = Calvert|first = James B.|date = 28 March 2003|url = http://www.du.edu/~jcalvert/phys/orbits.htm|title = Celestial Mechanics|publisher = University of Denver|access-date = 21 August 2006|archive-url = https://web.archive.org/web/20060907120741/http://www.du.edu/~jcalvert/phys/orbits.htm|archive-date = 7 September 2006}} [184] => [185] => The measurement of [[stellar parallax]] of nearby stars provides a fundamental baseline in the [[cosmic distance ladder]] that is used to measure the scale of the Universe. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared. Measurements of the [[radial velocity]] and [[proper motion]] of stars allow astronomers to plot the movement of these systems through the Milky Way galaxy. Astrometric results are the basis used to calculate the distribution of speculated [[dark matter]] in the galaxy.{{cite web|url=http://www.astro.virginia.edu/~rjp0i/museum/engines.html|title=Hall of Precision Astrometry|publisher=[[University of Virginia]] Department of Astronomy|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060826104509/http://www.astro.virginia.edu/~rjp0i/museum/engines.html|archive-date=26 August 2006 }} [186] => [187] => During the 1990s, the measurement of the [[stellar wobble]] of nearby stars was [[Methods of detecting extrasolar planets#Astrometry|used to detect]] large [[extrasolar planet]]s orbiting those stars.{{cite journal| author=Wolszczan, A.| author2=Frail, D. A.| title=A planetary system around the millisecond pulsar PSR1257+12| journal=Nature| date=1992| volume=355| issue=6356|pages=145–47| doi= 10.1038/355145a0| bibcode=1992Natur.355..145W| s2cid=4260368}} [188] => [189] => == Theoretical astronomy == [190] => {{Nucleosynthesis}} [191] => {{Main|Theoretical astronomy}} [192] => Theoretical astronomers use several tools including [[mathematical model|analytical models]] and [[computation]]al [[Numerical analysis|numerical simulations]]; each has its particular advantages. Analytical models of a process are better for giving broader insight into the heart of what is going on. Numerical models reveal the existence of phenomena and effects otherwise unobserved.{{cite journal|first=H.|last=Roth|title=A Slowly Contracting or Expanding Fluid Sphere and its Stability|journal=Physical Review |volume=39|issue=3|pages=525–29|date=1932|doi=10.1103/PhysRev.39.525|bibcode = 1932PhRv...39..525R }}{{cite journal |first=A.S.|last=Eddington|title=Internal Constitution of the Stars|journal=Science|publisher=Cambridge University Press|date=1926|volume=52|issue=1341|pages=233–40|doi=10.1126/science.52.1341.233|url=https://books.google.com/books?id=hJW3JbhnFQMC&pg=PA182|isbn=978-0-521-33708-3|pmid=17747682|bibcode=1920Sci....52..233E |bibcode-access=free |access-date=4 November 2020|archive-date=17 August 2021|archive-url=https://web.archive.org/web/20210817020341/https://books.google.com/books?id=hJW3JbhnFQMC&pg=PA182|url-status=live}} [193] => [194] => Theorists in astronomy endeavor to create theoretical models that are based on existing observations and known physics, and to predict observational consequences of those models. The observation of phenomena predicted by a model allows astronomers to select between several alternative or conflicting models. Theorists also modify existing models to take into account new observations. In some cases, a large amount of observational data that is inconsistent with a model may lead to abandoning it largely or completely, as for [[geocentric theory]], the existence of [[luminiferous aether]], and the [[steady-state model]] of cosmic evolution. [195] => [196] => Phenomena modeled by theoretical astronomers include: [197] => * [[stellar dynamics]] and [[Stellar evolution|evolution]] [198] => * [[galaxy formation and evolution|galaxy formation]] [199] => * [[large-scale structure of the universe|large-scale distribution]] of matter in the [[Universe]] [200] => * the origin of [[cosmic ray]]s [201] => * [[general relativity]] and [[physical cosmology]], including [[string cosmology]] and [[astroparticle physics]]. [202] => [203] => Modern theoretical astronomy reflects dramatic advances in observation since the 1990s, including studies of the [[cosmic microwave background]], distant [[supernovae]] and [[redshift survey|galaxy redshifts]], which have led to the development of a [[Lambda-CDM model|standard model of cosmology]]. This model requires the universe to contain large amounts of [[dark matter]] and [[dark energy]] whose nature is currently not well understood, but the model gives detailed predictions that are in excellent agreement with many diverse observations.{{cite journal | url=http://pdg.ge.infn.it/2011/reviews/rpp2011-rev-cosmological-parameters.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://pdg.ge.infn.it/2011/reviews/rpp2011-rev-cosmological-parameters.pdf |archive-date=2022-10-09 |url-status=live | title=2013 Review of Particle Physics | author=Beringer, J. | author2=et al. (Particle Data Group) | journal=Phys. Rev. D | date=2012 | volume=86 | issue=1 | page=010001|doi=10.1103/PhysRevD.86.010001|bibcode = 2012PhRvD..86a0001B | doi-access=free }} [204] => [205] => == Specific subfields == [206] => [207] => === Astrophysics === [208] => {{main |Astrophysics}} [209] => [[File:Observable Universe logarithmic illustration (circular layout english annotations).png|thumb|Astrophysics applies [[physics]] and [[chemistry]] to understand the measurements made by astronomy. Representation of the Observable Universe that includes images from [[Hubble Space Telescope|Hubble]] and other [[List of optical telescopes|telescopes]].]] [210] => [211] => Astrophysics is the branch of astronomy that employs the principles of physics and [[chemistry]] "to ascertain the nature of the [[astronomical object]]s, rather than their positions or motions in space".{{Cite journal | last = Keeler | first = James E. | author-link = James E. Keeler | title = The Importance of Astrophysical Research and the Relation of Astrophysics to the Other Physical Sciences | journal = The Astrophysical Journal | volume = 6 | issue = 4 | pages = 271–88 | date = November 1897 | bibcode = 1897ApJ.....6..271K |doi = 10.1086/140401| pmid = 17796068 | quote =[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 space—''what'' they are, rather than ''where'' they are.… That which is perhaps most characteristic of astrophysics is the special prominence which it gives to the study of radiation.| doi-access = free }}{{cite web | title=astrophysics | publisher=Merriam-Webster, Incorporated | url=http://www.merriam-webster.com/dictionary/astrophysics | access-date=22 May 2011 | archive-url= https://web.archive.org/web/20110610085146/http://www.merriam-webster.com/dictionary/astrophysics| archive-date= 10 June 2011 | url-status= live}} Among the objects studied are the [[Sun]], other [[star]]s, [[galaxy|galaxies]], [[extrasolar planet]]s, the [[interstellar medium]] and the [[cosmic microwave background]].{{cite web|url=https://science.nasa.gov/astrophysics/focus-areas/|title=Focus Areas – NASA Science|work=nasa.gov|access-date=12 November 2018|archive-date=16 May 2017|archive-url=https://web.archive.org/web/20170516154030/https://science.nasa.gov/astrophysics/focus-areas|url-status=live}}{{cite encyclopedia|url=https://www.britannica.com/EBchecked/topic/40047/astronomy|title=astronomy|encyclopedia=Encyclopædia Britannica|access-date=12 November 2018|archive-date=10 May 2015|archive-url=https://web.archive.org/web/20150510024116/https://www.britannica.com/EBchecked/topic/40047/astronomy|url-status=live}} Their emissions are examined across all parts of the [[electromagnetic spectrum]], and the properties examined include [[luminosity]], [[density]], [[temperature]], and [[chemistry|chemical]] composition. 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]]. [212] => [213] => In practice, modern astronomical research often involves a substantial amount of work in the realms of [[Theoretical physics|theoretical]] and observational physics. Some areas of study for astrophysicists include their attempts to determine the properties of [[dark matter]], [[dark energy]], and [[black holes]]; whether or not [[time travel]] is possible, [[wormhole]]s can form, or the [[multiverse]] exists; and the [[Cosmogony|origin]] and [[ultimate fate of the universe]]. Topics also studied by theoretical astrophysicists include [[Formation and evolution of the Solar System|Solar System formation and evolution]]; [[stellar dynamics]] and [[Stellar evolution|evolution]]; [[galaxy formation and evolution]]; [[magnetohydrodynamics]]; [[large-scale structure of the universe|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]]. [214] => [215] => === Astrochemistry === [216] => {{main|Astrochemistry}} [217] => Astrochemistry is the study of the abundance and reactions of [[molecule]]s in the [[Universe]], and their interaction with [[radiation]]. The discipline is an overlap of astronomy and [[chemistry]]. The word "astrochemistry" may be applied to both the [[Solar System]] and the [[interstellar medium]]. The study of the abundance of elements and [[isotope]] ratios in Solar System objects, such as [[meteorite]]s, is also called [[cosmochemistry]], while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of [[molecular cloud|molecular gas clouds]] is of special interest, because it is from these clouds that solar systems form. Studies in this field contribute to the understanding of the [[formation of the Solar System]], Earth's origin and geology, [[abiogenesis]], and the origin of climate and oceans.{{Cite news|url=https://www.cfa.harvard.edu/research/amp-rg/astrochemistry|title=Astrochemistry|date=15 July 2013|newspaper=www.cfa.harvard.edu/|access-date=20 November 2016|archive-url=https://web.archive.org/web/20161120211934/https://www.cfa.harvard.edu/research/amp-rg/astrochemistry|archive-date=20 November 2016}} [218] => [219] => === Astrobiology === [220] => {{main|Astrobiology}} [221] => Astrobiology is an interdisciplinary scientific field concerned with the [[abiogenesis|origins]], [[Protocell|early evolution]], distribution, and future of [[life]] in the [[universe]]. Astrobiology considers the question of whether [[extraterrestrial life]] exists, and how humans can detect it if it does.{{cite web| url=http://astrobiology.nasa.gov/about-astrobiology/ |title=About Astrobiology |access-date=20 October 2008 |date=21 January 2008 |work=NASA Astrobiology Institute |publisher=NASA | archive-url= https://web.archive.org/web/20081011192341/http://astrobiology.nasa.gov/about-astrobiology/| archive-date= 11 October 2008}} The term exobiology is similar.[http://www.merriam-webster.com/dictionary/exobiology Mirriam Webster Dictionary entry "Exobiology"] {{Webarchive|url=https://web.archive.org/web/20180904084642/https://www.merriam-webster.com/dictionary/exobiology |date=4 September 2018 }} (accessed 11 April 2013) [222] => [223] => Astrobiology makes use of [[molecular biology]], [[biophysics]], [[biochemistry]], [[chemistry]], astronomy, [[physical cosmology]], [[exoplanetology]] and [[geology]] to investigate the possibility of life on other worlds and help recognize [[biosphere]]s that might be different from that on Earth.{{cite book |title=The life and death of planet Earth |last1=Ward |first1=P.D. |author2=Brownlee, D. |date=2004 |publisher=Owl Books |location=New York |isbn=978-0-8050-7512-0 }} [[Abiogenesis|The origin]] and early evolution of life is an inseparable part of the discipline of astrobiology.{{cite web |url=https://link.springer.com/journal/11084 |title=Origins of Life and Evolution of Biospheres |work=Journal: Origins of Life and Evolution of Biospheres |access-date=6 April 2015 |archive-date=8 February 2020 |archive-url=https://web.archive.org/web/20200208140912/https://link.springer.com/journal/11084 |url-status=live }} Astrobiology concerns itself with interpretation of existing [[Scientific method|scientific data]], and although speculation is entertained to give context, astrobiology concerns itself primarily with [[hypotheses]] that fit firmly into existing [[scientific theories]]. [224] => [225] => This [[interdisciplinary]] field encompasses research on the origin of [[planetary system]]s, origins of [[List of interstellar and circumstellar molecules|organic compounds in space]], rock-water-carbon interactions, [[abiogenesis]] on Earth, [[planetary habitability]], research on [[biosignature]]s for life detection, and studies on the potential for [[extremophile|life to adapt to challenges]] on Earth and in [[outer space]].{{cite news |url=http://astrobiology.com/2016/03/release-of-the-first-roadmap-for-european-astrobiology.html |title=Release of the First Roadmap for European Astrobiology |work=European Science Foundation |publisher=Astrobiology Web |date=29 March 2016 |access-date=2 April 2016 |archive-date=10 June 2020 |archive-url=https://web.archive.org/web/20200610010327/http://astrobiology.com/2016/03/release-of-the-first-roadmap-for-european-astrobiology.html |url-status=live }}{{cite news |last=Corum |first=Jonathan |title=Mapping Saturn's Moons |url=https://www.nytimes.com/interactive/2015/12/18/science/space/nasa-cassini-maps-saturns-moons.html |date=18 December 2015 |work=[[The New York Times]] |access-date=18 December 2015 |archive-date=20 May 2020 |archive-url=https://web.archive.org/web/20200520124847/https://www.nytimes.com/interactive/2015/12/18/science/space/nasa-cassini-maps-saturns-moons.html |url-status=live }}{{cite news | last = Cockell | first = Charles S. | title = How the search for aliens can help sustain life on Earth | date = 4 October 2012 | url = http://edition.cnn.com/2012/10/02/world/europe/astrobiology-aliens-environment-opinion/index.html?hpt=hp_c4 | work = CNN News | access-date = 8 October 2012 | archive-date = 10 September 2016 | archive-url = https://web.archive.org/web/20160910182606/http://edition.cnn.com/2012/10/02/world/europe/astrobiology-aliens-environment-opinion/index.html?hpt=hp_c4 | url-status = live }} [226] => [227] => === Physical cosmology === [228] => {{Nature timeline}} [229] => {{Main|Physical cosmology}} [230] => [231] => [[Cosmology]] (from the Greek {{lang|grc|κόσμος}} ({{transliteration|grc|kosmos}}) "world, universe" and {{lang|grc|λόγος}} ({{transliteration|grc|logos}}) "word, study" or literally "logic") could be considered the study of the Universe as a whole. [232] => [233] => [[File:Hubble Extreme Deep Field (full resolution).png|thumb|[[Hubble Extreme Deep Field]]]] [234] => [235] => Observations of the [[large-scale structure of the Universe]], a branch known as [[physical cosmology]], have provided a deep understanding of the formation and evolution of the cosmos. Fundamental to modern cosmology is the well-accepted theory of the [[Big Bang]], wherein our Universe began at a single [[point in time]], and thereafter [[metric expansion of space|expanded]] over the course of 13.8 billion years{{cite web [236] => |title = Cosmic Detectives [237] => |url = http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives [238] => |publisher = The European Space Agency (ESA) [239] => |date = 2 April 2013 [240] => |access-date = 15 April 2013 [241] => |archive-date = 11 February 2019 [242] => |archive-url = https://web.archive.org/web/20190211204726/http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives [243] => |url-status = live [244] => }} to its present condition. The concept of the Big Bang can be traced back to the discovery of the [[Cosmic microwave background radiation|microwave background radiation]] in 1965.{{cite book|last=Dodelson|first=Scott|title=Modern cosmology|date=2003|isbn=978-0-12-219141-1|publisher=[[Academic Press]]|pages=1–22}} [245] => [246] => In the course of this expansion, the Universe underwent several evolutionary stages. In the very early moments, it is theorized that the Universe experienced a very rapid [[cosmic inflation]], which homogenized the starting conditions. Thereafter, [[Big Bang nucleosynthesis|nucleosynthesis]] produced the elemental abundance of the early Universe. (See also [[nucleocosmochronology]].) [247] => [248] => When the first neutral [[atom]]s formed from a sea of primordial ions, space became transparent to radiation, releasing the energy viewed today as the microwave background radiation. The expanding Universe then underwent a Dark Age due to the lack of stellar energy sources.{{cite web|last = Hinshaw|first = Gary|date = 13 July 2006|url=http://map.gsfc.nasa.gov/m_uni.html|title = Cosmology 101: The Study of the Universe|publisher = NASA WMAP|access-date =10 August 2006| archive-url= https://web.archive.org/web/20060813053535/http://map.gsfc.nasa.gov/m_uni.html| archive-date= 13 August 2006 | url-status= live}} [249] => [250] => A hierarchical structure of matter began to form from minute variations in the mass density of space. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars, the [[Population III stars]]. These massive stars triggered the [[reionization]] process and are believed to have created many of the heavy elements in the early Universe, which, through nuclear decay, create lighter elements, allowing the cycle of nucleosynthesis to continue longer.Dodelson, 2003, pp. 216–61 [251] => [252] => Gravitational aggregations clustered into filaments, leaving voids in the gaps. Gradually, organizations of gas and dust merged to form the first primitive galaxies. Over time, these pulled in more matter, and were often organized into [[Galaxy groups and clusters|groups and clusters]] of galaxies, then into larger-scale superclusters.{{cite web|url=http://www.damtp.cam.ac.uk/user/gr/public/gal_lss.html|title = Galaxy Clusters and Large-Scale Structure|publisher = University of Cambridge|access-date =8 September 2006| archive-url= https://web.archive.org/web/20061010041120/http://www.damtp.cam.ac.uk/user/gr/public/gal_lss.html| archive-date= 10 October 2006 | url-status= live}} [253] => [254] => Fundamental to the structure of the Universe is the existence of [[dark matter]] and [[dark energy]]. These are now thought to be its dominant components, forming 96% of the mass of the Universe. For this reason, much effort is expended in trying to understand the physics of these components.{{cite web|last = Preuss|first = Paul|url=http://www.lbl.gov/Science-Articles/Archive/dark-energy.html|title = Dark Energy Fills the Cosmos|publisher = U.S. Department of Energy, Berkeley Lab|access-date =8 September 2006| archive-url= https://web.archive.org/web/20060811215815/http://www.lbl.gov/Science-Articles/Archive/dark-energy.html| archive-date= 11 August 2006 | url-status= live}} [255] => [256] => === Extragalactic astronomy === [257] => [258] => [[File:grav.lens1.arp.750pix.jpg|thumb|This image shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the [[gravitational lens]] effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.]] [259] => {{Main|Extragalactic astronomy}} [260] => The study of objects outside our galaxy is a branch of astronomy concerned with the [[Galaxy formation and evolution|formation and evolution of galaxies]], their morphology (description) and [[Galaxy morphological classification|classification]], the observation of [[Active galaxy|active galaxies]], and at a larger scale, the [[Galaxy groups and clusters|groups and clusters of galaxies]]. Finally, the latter is important for the understanding of the [[large-scale structure of the cosmos]]. [261] => [262] => Most [[galaxy|galaxies]] are organized into distinct shapes that allow for classification schemes. They are commonly divided into [[spiral galaxy|spiral]], [[elliptical galaxy|elliptical]] and [[irregular galaxy|Irregular]] galaxies.{{cite web|last = Keel|first = Bill|date = 1 August 2006|url=http://www.astr.ua.edu/keel/galaxies/classify.html|title = Galaxy Classification|publisher = University of Alabama|access-date =8 September 2006| archive-url= https://web.archive.org/web/20060901074027/http://www.astr.ua.edu/keel/galaxies/classify.html| archive-date= 1 September 2006 | url-status= live}} [263] => [264] => As the name suggests, an elliptical galaxy has the cross-sectional shape of an [[ellipse]]. The stars move along [[randomness|random]] orbits with no preferred direction. These galaxies contain little or no interstellar dust, few star-forming regions, and older stars.{{Rp|pages=877–878}} Elliptical galaxies may have been formed by other galaxies merging.{{Rp|page=939}} [265] => [266] => A spiral galaxy is organized into a flat, rotating disk, usually with a prominent bulge or bar at the center, and trailing bright arms that spiral outward. The arms are dusty regions of star formation within which massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Both the [[Milky Way]] and one of our nearest galaxy neighbors, the [[Andromeda Galaxy]], are spiral galaxies.{{Rp|page=875}} [267] => [268] => Irregular galaxies are chaotic in appearance, and are neither spiral nor elliptical.{{Rp|page=879}} About a quarter of all galaxies are irregular, and the peculiar shapes of such galaxies may be the result of gravitational interaction.{{Cite web |date=2016-08-08 |title=A lopsided lynx |url=https://esahubble.org/images/potw1632a/ |access-date=2023-03-17 |website=esahubble.org |publisher=[[European Space Agency]] |language=en |archive-date=9 July 2021 |archive-url=https://web.archive.org/web/20210709183618/https://esahubble.org/images/potw1632a/ |url-status=live }} [269] => [270] => An active galaxy is a formation that emits a significant amount of its energy from a source other than its stars, dust and gas. It is powered by a compact region at the core, thought to be a supermassive black hole that is emitting radiation from in-falling material.{{Rp|page=907}} A [[radio galaxy]] is an active galaxy that is very luminous in the radio portion of the spectrum, and is emitting immense plumes or lobes of gas. Active galaxies that emit shorter frequency, high-energy radiation include [[Seyfert galaxy|Seyfert galaxies]], [[quasar]]s, and [[blazar]]s. Quasars are believed to be the most consistently luminous objects in the known universe.{{cite web|url=http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html|title=Active Galaxies and Quasars|publisher=NASA|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060831033713/http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html|archive-date=31 August 2006 }} [271] => [272] => The [[large-scale structure of the cosmos]] is represented by groups and clusters of galaxies. This structure is organized into a hierarchy of groupings, with the largest being the [[supercluster]]s. The collective matter is formed into [[Galaxy filament|filaments]] and walls, leaving large [[Void (astronomy)|voids]] between.{{cite book|first=Michael|last=Zeilik|title=Astronomy: The Evolving Universe|edition=8th|publisher=Wiley|date=2002|isbn=978-0-521-80090-7}} [273] => [274] => === Galactic astronomy === [275] => [276] => [[File:Milky Way Spiral Arm.svg|right|thumb|Observed structure of the [[Milky Way]]'s spiral arms]] [277] => {{Main|Galactic astronomy}} [278] => The [[Solar System]] orbits within the [[Milky Way]], a [[barred spiral galaxy]] that is a prominent member of the [[Local Group]] of galaxies. It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view.{{Rp|pages=837–842,944}} [279] => [280] => In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a [[supermassive black hole]] at its center. This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger, [[Stellar population|population I]] stars. The disk is surrounded by a [[Galactic spheroid|spheroid halo]] of older, [[population II]] stars, as well as relatively dense concentrations of stars known as [[globular cluster]]s.{{cite web|url=http://www.mpe.mpg.de/ir/GC/index.php|title=The Galactic Centre|last=Ott|first=Thomas|date=24 August 2006|publisher=Max-Planck-Institut für extraterrestrische Physik|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060904140550/http://www.mpe.mpg.de/ir/GC/index.php|archive-date=4 September 2006 }} [281] => [282] => Between the stars lies the [[interstellar medium]], a region of sparse matter. In the densest regions, [[molecular cloud]]s of [[Hydrogen|molecular hydrogen]] and other elements create star-forming regions. These begin as a compact [[pre-stellar core]] or [[dark nebula]]e, which concentrate and collapse (in volumes determined by the [[Jeans length]]) to form compact protostars.{{cite book|first=Michael David|last=Smith|date=2004|pages=53–86|title=The Origin of Stars|chapter=Cloud formation, Evolution and Destruction|publisher=Imperial College Press|isbn=978-1-86094-501-4|chapter-url=https://books.google.com/books?id=UVgBoqZg8a4C|access-date=26 August 2020|archive-date=13 August 2021|archive-url=https://web.archive.org/web/20210813210429/https://books.google.com/books?id=UVgBoqZg8a4C|url-status=live}} [283] => [284] => As the more massive stars appear, they transform the cloud into an [[H II region]] (ionized atomic hydrogen) of glowing gas and plasma. The [[Solar wind|stellar wind]] and supernova explosions from these stars eventually cause the cloud to disperse, often leaving behind one or more young [[open cluster]]s of stars. These clusters gradually disperse, and the stars join the population of the Milky Way.{{cite book|first=Michael David|last=Smith|date=2004|pages=185–99|title=The Origin of Stars|chapter=Massive stars|publisher=Imperial College Press|isbn=978-1-86094-501-4|chapter-url=https://books.google.com/books?id=UVgBoqZg8a4C|access-date=26 August 2020|archive-date=13 August 2021|archive-url=https://web.archive.org/web/20210813210429/https://books.google.com/books?id=UVgBoqZg8a4C|url-status=live}} [285] => [286] => Kinematic studies of matter in the Milky Way and other galaxies have demonstrated that there is more mass than can be accounted for by visible matter. A [[dark matter halo]] appears to dominate the mass, although the nature of this dark matter remains undetermined.{{cite journal|author=Van den Bergh, Sidney|title=The Early History of Dark Matter|journal=Publications of the Astronomical Society of the Pacific|date=1999|volume=111|issue=760|pages=657–60|doi=10.1086/316369|arxiv = astro-ph/9904251 |bibcode = 1999PASP..111..657V |s2cid=5640064}} [287] => [288] => === Stellar astronomy === [289] => [[File:Ant Nebula.jpg|thumb|[[Mz 3]], often referred to as the Ant planetary nebula. Ejecting gas from the dying central star shows symmetrical patterns unlike the chaotic patterns of ordinary explosions.]] [290] => {{Main|Star}} [291] => {{see also|Solar astronomy}} [292] => The study of stars and [[stellar evolution]] is fundamental to our understanding of the Universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior.Harpaz, 1994, pp. 7–18 [[Star formation]] occurs in dense regions of dust and gas, known as [[Dark nebula|giant molecular clouds]]. When destabilized, cloud fragments can collapse under the influence of gravity, to form a [[protostar]]. A sufficiently dense, and hot, core region will trigger [[nuclear fusion]], thus creating a [[main-sequence star]]. [293] => [294] => Almost all elements heavier than [[hydrogen]] and [[helium]] were [[nucleosynthesis|created]] inside the cores of stars. [295] => [296] => The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it fuses its hydrogen fuel into helium in its core. Over time, this hydrogen fuel is completely converted into helium, and the star begins to [[Stellar evolution|evolve]]. The fusion of helium requires a higher core temperature. A star with a high enough core temperature will push its outer layers outward while increasing its core density. The resulting [[red giant]] formed by the expanding outer layers enjoys a brief life span, before the helium fuel in the core is in turn consumed. Very massive stars can also undergo a series of evolutionary phases, as they fuse increasingly heavier elements.Harpaz, 1994 [297] => [298] => The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse [[supernova]]e;Harpaz, 1994, pp. 173–78 while smaller stars blow off their outer layers and leave behind the inert core in the form of a [[white dwarf]]. The ejection of the outer layers forms a [[planetary nebula]].Harpaz, 1994, pp. 111–18 The remnant of a supernova is a dense [[neutron star]], or, if the stellar mass was at least three times that of the Sun, a [[black hole]].{{cite book|editor= Audouze, Jean|editor2= Israel, Guy|title=The Cambridge Atlas of Astronomy|edition=3rd|publisher=Cambridge University Press|date=1994|isbn=978-0-521-43438-6}} Closely orbiting binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova.Harpaz, 1994, pp. 189–210 Planetary nebulae and supernovae distribute the "[[metallicity|metals]]" produced in the star by fusion to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone.Harpaz, 1994, pp. 245–56 [299] => [300] => === Solar astronomy === [301] => [[File:Uvsun trace big.jpg|thumb|An [[ultraviolet]] image of the Sun's active [[photosphere]] as viewed by the [[TRACE]] space telescope. ''[[NASA]] photo'']] [302] => [[File:Observatórium Lomnický štít 1.jpg|thumb|Solar observatory [[Lomnický štít]] ([[Slovakia]]) built in 1962]] [303] => {{Main|Sun}} [304] => {{See also|Solar telescope}} [305] => At a distance of about eight light-minutes, the most frequently studied star is the [[Sun]], a typical main-sequence [[dwarf star]] of [[stellar class]] G2 V, and about 4.6 billion years (Gyr) old. The Sun is not considered a [[variable star]], but it does undergo periodic changes in activity known as the [[sunspot cycle]]. This is an 11-year oscillation in [[Wolf number|sunspot number]]. Sunspots are regions of lower-than- average temperatures that are associated with intense magnetic activity.{{cite web|url=http://www.talkorigins.org/faqs/faq-solar.html|title=The Solar FAQ|last=Johansson|first=Sverker|author-link=Sverker Johansson|date=27 July 2003|publisher=Talk.Origins Archive|access-date=11 August 2006|archive-url=https://web.archive.org/web/20060907235636/http://www.talkorigins.org/faqs/faq-solar.html|archive-date=7 September 2006 |url-status=live}} [306] => [307] => The Sun has steadily increased in luminosity by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.{{cite web|url=http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page|title=Environmental issues: essential primary sources|last1=Lerner|first1=K. Lee|first2=Brenda Wilmoth|date=2006|publisher=Thomson Gale|archive-url=https://archive.today/20120710152134/http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?v3=1&DB=local&CMD=010a+2006000857&CNT=10+records+per+page|archive-date=10 July 2012|last2=Lerner|access-date=17 November 2016}} The [[Maunder minimum]], for example, is believed to have caused the [[Little Ice Age]] phenomenon during the [[Middle Ages]].{{cite web|author=Pogge, Richard W. |date=1997 |url=http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html |title=The Once & Future Sun |format=lecture notes |work=New Vistas in Astronomy |access-date=3 February 2010 |archive-url=https://web.archive.org/web/20050527094435/http://www-astronomy.mps.ohio-state.edu/Vistas/ |archive-date=27 May 2005 }} [308] => [309] => At the center of the Sun is the core region, a volume of sufficient temperature and pressure for [[nuclear fusion]] to occur. Above the core is the [[radiation zone]], where the plasma conveys the energy flux by means of radiation. Above that is the [[convection zone]] where the gas material transports energy primarily through physical displacement of the gas known as convection. It is believed that the movement of mass within the convection zone creates the magnetic activity that generates sunspots. The visible outer surface of the Sun is called the [[photosphere]]. Above this layer is a thin region known as the [[chromosphere]]. This is surrounded by a transition region of rapidly increasing temperatures, and finally by the super-heated [[solar corona|corona]].{{Rp|pages=498–502}} [310] => [311] => A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches the [[heliopause (astronomy)|heliopause]]. As the solar wind passes the Earth, it interacts with the [[Earth's magnetic field]] ([[magnetosphere]]) and deflects the solar wind, but traps some creating the [[Van Allen radiation belt]]s that envelop the Earth. The [[aurora (astronomy)|aurora]] are created when solar wind particles are guided by the magnetic flux lines into the Earth's polar regions where the lines then descend into the [[Earth's atmosphere|atmosphere]].{{cite web|author = Stern, D.P.|author2 = Peredo, M.|date = 28 September 2004|url=http://www-istp.gsfc.nasa.gov/Education/Intro.html|title = The Exploration of the Earth's Magnetosphere|publisher = NASA|access-date =22 August 2006| archive-url= https://web.archive.org/web/20060824003619/http://www-istp.gsfc.nasa.gov/Education/Intro.html| archive-date= 24 August 2006 | url-status= live}} [312] => [313] => === Planetary science === [314] => [[File:dust.devil.mars.arp.750pix.jpg|thumb|The black spot at the top is a [[dust devil]] climbing a crater wall on [[Mars]]. This moving, swirling column of [[Atmosphere of Mars|Martian atmosphere]] (comparable to a terrestrial [[tornado]]) created the long, dark streak.]] [315] => {{Main|Planetary science|Planetary geology}} [316] => Planetary science is the study of the assemblage of [[planet]]s, [[natural satellite|moons]], [[dwarf planet]]s, [[comet]]s, [[asteroid]]s, and other bodies orbiting the Sun, as well as extrasolar planets. The [[Solar System]] has been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of the Sun's planetary system, although many new discoveries are still being made.{{cite book|url=http://marswatch.tn.cornell.edu/rsm.html|title=Remote Sensing for the Earth Sciences: Manual of Remote Sensing|date=2004|publisher=John Wiley & Sons|edition=3rd|author=Bell III, J. F.|author2=Campbell, B.A.|author3=Robinson, M.S.|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060811220029/http://marswatch.tn.cornell.edu/rsm.html|archive-date=11 August 2006 }} [317] => [318] => The Solar System is divided into the [[inner Solar System]] (subdivided into the inner planets and the [[asteroid belt]]), the [[outer Solar System]] (subdivided into the outer planets and [[Centaurs (minor planets)|centaurs]]), comets, the trans-Neptunian region (subdivided into the [[Kuiper belt]], and the [[scattered disc]]) and the farthest regions (e.g., boundaries of the [[heliosphere]], and the [[Oort Cloud]], which may extend as far as a light-year). The inner [[terrestrial planet]]s consist of [[Mercury (planet)|Mercury]], [[Venus]], Earth, and [[Mars]]. The outer [[giant planet]]s are the [[gas giant]]s ([[Jupiter]] and [[Saturn]]) and the [[ice giant]]s ([[Uranus]] and [[Neptune]]).{{cite web|author = Grayzeck, E.|author2 = Williams, D.R.| date = 11 May 2006|url=http://nssdc.gsfc.nasa.gov/planetary/|title = Lunar and Planetary Science|publisher = NASA|access-date =21 August 2006| archive-url= https://web.archive.org/web/20060820173205/http://nssdc.gsfc.nasa.gov/planetary/| archive-date= 20 August 2006 | url-status= live}} [319] => [320] => The planets were formed 4.6 billion years ago in the [[protoplanetary disk]] that surrounded the early Sun. Through a process that included gravitational attraction, collision, and accretion, the disk formed clumps of matter that, with time, became protoplanets. The [[radiation pressure]] of the [[solar wind]] then expelled most of the unaccreted matter, and only those planets with sufficient mass retained their gaseous atmosphere. The planets continued to sweep up, or eject, the remaining matter during a period of intense bombardment, evidenced by the many [[impact crater]]s on the Moon. During this period, some of the protoplanets may have collided and one such collision may have [[giant impact hypothesis|formed the Moon]].{{cite journal|last=Montmerle|first=Thierry|author2=Augereau, Jean-Charles|author3= Chaussidon, Marc|title=Solar System Formation and Early Evolution: the First 100 Million Years|journal=Earth, Moon, and Planets|volume=98|issue=1–4|pages=39–95|date=2006|doi=10.1007/s11038-006-9087-5| bibcode=2006EM&P...98...39M|s2cid=120504344|display-authors=etal}} [321] => [322] => Once a planet reaches sufficient mass, the materials of different densities segregate within, during [[planetary differentiation]]. This process can form a stony or metallic core, surrounded by a mantle and an outer crust. The core may include solid and liquid regions, and some planetary cores generate their own [[magnetic field]], which can protect their atmospheres from solar wind stripping.Montmerle, 2006, pp. 87–90 [323] => [324] => A planet or moon's interior heat is produced from the collisions that created the body, by the decay of radioactive materials (''e.g.'' [[uranium]], [[thorium]], and [[26Al|26Al]]), or [[tidal acceleration|tidal heating]] caused by interactions with other bodies. Some planets and moons accumulate enough heat to drive geologic processes such as [[volcanism]] and tectonics. Those that accumulate or retain an [[atmosphere]] can also undergo surface [[erosion]] from wind or water. Smaller bodies, without tidal heating, cool more quickly; and their geological activity ceases with the exception of impact cratering.{{cite book|editor=Beatty, J.K.|editor2=Petersen, C.C.|editor3=Chaikin, A.|title=The New Solar System|publisher=Cambridge press|url=https://books.google.com/books?id=iOezyHMVAMcC&pg=PA70|page=70edition = 4th|date=1999|isbn=978-0-521-64587-4|access-date=26 August 2020|archive-date=30 March 2015|archive-url=https://web.archive.org/web/20150330114739/http://books.google.com/books?id=iOezyHMVAMcC&pg=PA70|url-status=live}} [325] => [326] => == Interdisciplinary studies == [327] => Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. [[Archaeoastronomy]] is the study of ancient or traditional astronomies in their cultural context, utilizing [[archaeology|archaeological]] and [[anthropology|anthropological]] evidence. [[Astrobiology]] is the study of the advent and evolution of biological systems in the Universe, with particular emphasis on the possibility of non-terrestrial life. [[Astrostatistics]] is the application of statistics to astrophysics to the analysis of a vast amount of observational astrophysical data.{{citation | last=Hilbe | first=Joseph M. | title=Wiley Stats ''Ref'': Statistics Reference Online | chapter=Astrostatistics | publisher=Wiley | date=2017 | doi=10.1002/9781118445112.stat07961 | pages=1–5| isbn=9781118445112 }} [328] => [329] => The study of [[chemical]]s found in space, including their formation, interaction and destruction, is called [[astrochemistry]]. These substances are usually found in [[molecular cloud]]s, although they may also appear in low-temperature stars, brown dwarfs and planets. [[Cosmochemistry]] is the study of the chemicals found within the Solar System, including the origins of the elements and variations in the [[isotope]] ratios. Both of these fields represent an overlap of the disciplines of astronomy and chemistry. As "[[forensic astronomy]]", finally, methods from astronomy have been used to solve problems of art history{{cite web |url=https://gizmodo.com/scientists-used-the-stars-to-confirm-when-a-famous-sapp-1776569251 |title=Scientists Used the Stars to Confirm When a Famous Sapphic Poem Was Written |website=Gizmodo |first=Jennifer |last=Ouellette |date=2016-05-13 |access-date=2023-03-24 |archive-date=24 March 2023 |archive-url=https://web.archive.org/web/20230324165949/https://gizmodo.com/scientists-used-the-stars-to-confirm-when-a-famous-sapp-1776569251 |url-status=live }}{{cite web |url=https://www.scientificamerican.com/article/forensic-astronomy-reveals-the-secrets-of-an-iconic-ansel-adams-photo/ |title='Forensic Astronomy' Reveals the Secrets of an Iconic Ansel Adams Photo |first=Summer |last=Ash |website=Scientific American |date=2018-04-17 |access-date=2023-03-24 |archive-date=24 March 2023 |archive-url=https://web.archive.org/web/20230324165949/https://www.scientificamerican.com/article/forensic-astronomy-reveals-the-secrets-of-an-iconic-ansel-adams-photo/ |url-status=live }} and occasionally of law.{{cite book|first=Jordan D. |last=Marché |chapter=Epilogue |title=Theaters of Time and Space: American Planetaria, 1930–1970 |year=2005 |pages=170–178 |chapter-url=https://www.jstor.org/stable/j.ctt5hjd29.14 |publisher=Rutgers University Press |jstor=j.ctt5hjd29.14 |isbn=0-813-53576-X}} [330] => [331] => == Amateur astronomy == [332] => [[File:Telescope trailer 22.jpg|upright|thumb|Amateur astronomers can build their own equipment, and hold star parties and gatherings, such as [[Stellafane]].]] [333] => {{Main|Amateur astronomy}} [334] => [335] => Astronomy is one of the sciences to which amateurs can contribute the most.{{cite journal [336] => |last = Mims III|first = Forrest M. [337] => |title=Amateur Science—Strong Tradition, Bright Future [338] => |journal=Science|date=1999|volume=284|issue=5411 [339] => |pages=55–56 [340] => |doi=10.1126/science.284.5411.55 [341] => |quote=Astronomy has traditionally been among the most fertile fields for serious amateurs [...] [342] => |bibcode = 1999Sci...284...55M |s2cid = 162370774 [343] => }} [344] => [345] => Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with consumer-level equipment or [[Amateur telescope making|equipment that they build themselves]]. Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, [[meteor shower]]s, and a variety of [[deep-sky object]]s such as star clusters, galaxies, and nebulae. Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to observe all the objects in the Messier (110 objects) or Herschel 400 catalogues of points of interest in the night sky. One branch of amateur astronomy, [[astrophotography]], involves the taking of photos of the night sky. Many amateurs like to specialize in the observation of particular objects, types of objects, or types of events that interest them.{{cite web|url=http://www.amsmeteors.org/|title = The American Meteor Society|access-date =24 August 2006| archive-url= https://web.archive.org/web/20060822135040/http://www.amsmeteors.org/| archive-date= 22 August 2006 | url-status= live}}{{cite web|first=Jerry|last=Lodriguss|url=http://www.astropix.com/|title = Catching the Light: Astrophotography|access-date =24 August 2006| archive-url= https://web.archive.org/web/20060901185541/http://www.astropix.com/| archive-date= 1 September 2006 | url-status= live}} [346] => [347] => Most amateurs work at visible wavelengths, but many experiment with wavelengths outside the visible spectrum. This includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. The pioneer of amateur radio astronomy was [[Karl Guthe Jansky|Karl Jansky]], who started observing the sky at radio wavelengths in the 1930s. A number of amateur astronomers use either homemade telescopes or use radio telescopes which were originally built for astronomy research but which are now available to amateurs (''e.g.'' the [[One-Mile Telescope]]).{{cite web|author=Ghigo, F.|date = 7 February 2006|url=http://www.nrao.edu/whatisra/hist_jansky.shtml|title = Karl Jansky and the Discovery of Cosmic Radio Waves|publisher = National Radio Astronomy Observatory|access-date =24 August 2006| archive-url= https://web.archive.org/web/20060831105945/http://www.nrao.edu/whatisra/hist_jansky.shtml| archive-date= 31 August 2006 | url-status= live}}{{cite web|url=http://www.users.globalnet.co.uk/~arcus/cara/|title=Cambridge Amateur Radio Astronomers|access-date=24 August 2006|archive-date=24 May 2012|archive-url=https://archive.today/20120524/http://www.users.globalnet.co.uk/~arcus/cara/|url-status=live}} [348] => [349] => Amateur astronomers continue to make scientific contributions to the field of astronomy and it is one of the few scientific disciplines where amateurs can still make significant contributions. Amateurs can make occultation measurements that are used to refine the orbits of minor planets. They can also discover comets, and perform regular observations of variable stars. Improvements in digital technology have allowed amateurs to make impressive advances in the field of astrophotography.{{cite web| url= http://www.lunar-occultations.com/iota/iotandx.htm| title= The International Occultation Timing Association| access-date= 24 August 2006| archive-url= https://web.archive.org/web/20060821180723/http://www.lunar-occultations.com/iota/iotandx.htm| archive-date= 21 August 2006}}{{cite web|url=http://cbat.eps.harvard.edu/special/EdgarWilson.html |title=Edgar Wilson Award |publisher=IAU Central Bureau for Astronomical Telegrams |access-date=24 October 2010 |archive-url=https://web.archive.org/web/20101024202325/http://www.cbat.eps.harvard.edu/special/EdgarWilson.html |archive-date=24 October 2010 }}{{cite web|url=http://www.aavso.org/|title = American Association of Variable Star Observers|publisher = AAVSO|access-date =3 February 2010| archive-url= https://web.archive.org/web/20100202050715/http://www.aavso.org/| archive-date= 2 February 2010 | url-status= live}} [350] => [351] => == Unsolved problems in astronomy == [352] => {{Main|List of unsolved problems in astronomy}} [353] => In the 21st century there remain important unanswered questions in astronomy. Some are cosmic in scope: for example, what are [[dark matter]] and [[dark energy]]? These dominate the evolution and fate of the cosmos, yet their true nature remains unknown.{{cite web|url=http://www.pnl.gov/energyscience/01-02/11-questions/11questions.htm [354] => |title = 11 Physics Questions for the New Century [355] => |publisher = Pacific Northwest National Laboratory [356] => |access-date =12 August 2006 |archive-url = https://web.archive.org/web/20060203152634/http://www.pnl.gov/energyscience/01-02/11-questions/11questions.htm |archive-date = 3 February 2006}} What will be the [[ultimate fate of the universe]]?{{cite web [357] => |last = Hinshaw|first = Gary|date = 15 December 2005 [358] => |url = http://map.gsfc.nasa.gov/m_uni/uni_101fate.html [359] => |title = What is the Ultimate Fate of the Universe? [360] => |publisher = NASA WMAP|access-date =28 May 2007| archive-url= https://web.archive.org/web/20070529145436/http://map.gsfc.nasa.gov/m_uni/uni_101fate.html| archive-date= 29 May 2007 | url-status= live}} Why is the abundance of [[lithium]] in the cosmos four times lower than predicted by the standard [[Big Bang]] model?{{Cite journal|last1=Howk|first1=J. Christopher|last2=Lehner|first2=Nicolas|last3=Fields|first3=Brian D.|last4=Mathews|first4=Grant J.|date=6 September 2012|title=Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud|journal=Nature|language=en|volume=489|issue=7414|pages=121–23|doi=10.1038/nature11407|pmid=22955622|arxiv = 1207.3081 |bibcode = 2012Natur.489..121H |s2cid=205230254}} Others pertain to more specific classes of phenomena. For example, is the [[Solar System]] normal or atypical?{{cite journal | title=How special is the Solar system? | last1=Beer | first1=M. E. | last2=King | first2=A. R. | last3=Livio | first3=M. | last4=Pringle | first4=J. E. | journal=Monthly Notices of the Royal Astronomical Society | volume=354 | issue=3 | pages=763–768 | date=November 2004 | doi=10.1111/j.1365-2966.2004.08237.x | arxiv=astro-ph/0407476 | bibcode=2004MNRAS.354..763B | s2cid=119552423 }} What is the origin of the stellar mass spectrum? That is, why do astronomers observe the same distribution of stellar masses—the [[initial mass function]]—apparently regardless of the initial conditions?{{cite journal [361] => |last = Kroupa|first = Pavel [362] => |title=The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems [363] => |journal=Science|date=2002|volume=295|issue=5552 [364] => |pages=82–91 [365] => |doi=10.1126/science.1067524 [366] => |pmid=11778039 [367] => |arxiv = astro-ph/0201098 |bibcode = 2002Sci...295...82K [368] => |s2cid = 14084249 [369] => }} Likewise, questions remain about the formation of the [[protogalaxy|first galaxies]],{{cite web|title=FAQ – How did galaxies form?|url=http://origins.stsci.edu/faq/galaxies.html|publisher=NASA|access-date=28 July 2015|archive-url=https://web.archive.org/web/20150628054952/http://origins.stsci.edu/faq/galaxies.html|archive-date=28 June 2015}} the origin of [[supermassive black hole]]s,{{cite web|title=Supermassive Black Hole|url=http://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole|publisher=Swinburne University|access-date=28 July 2015|archive-date=14 August 2020|archive-url=https://web.archive.org/web/20200814110807/https://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole|url-status=live}} the source of [[ultra-high-energy cosmic ray]]s,{{cite journal|journal=Annual Review of Astronomy and Astrophysics|title=The Origin of Ultra-High-Energy Cosmic Rays|last=Hillas|first=A.M.|volume=22|date=September 1984|doi=10.1146/annurev.aa.22.090184.002233|pages=425–44|quote=This poses a challenge to these models, because [...]|bibcode = 1984ARA&A..22..425H }} and more. [370] => [371] => Is there other [[Extraterrestrial life|life in the Universe]]? Especially, is there other intelligent life? If so, what is the explanation for the [[Fermi paradox]]? The existence of life elsewhere has important scientific and philosophical implications.{{cite web [372] => |url=http://www.astrobio.net/debate/236/complex-life-elsewhere-in-the-universe [373] => |archive-url=https://web.archive.org/web/20110628214416/http://www.astrobio.net/debate/236/complex-life-elsewhere-in-the-universe [374] => |archive-date=28 June 2011 [375] => |url-status=usurped [376] => |title = Rare Earth: Complex Life Elsewhere in the Universe? [377] => |work = Astrobiology Magazine|access-date =12 August 2006|date=15 July 2002 [378] => }}{{cite web|url=http://www.bigear.org/vol1no2/sagan.htm|title=The Quest for Extraterrestrial Intelligence|last=Sagan|first=Carl|work=Cosmic Search Magazine|access-date=12 August 2006|archive-url=https://web.archive.org/web/20060818144558/http://www.bigear.org/vol1no2/sagan.htm|archive-date=18 August 2006 |url-status=live}} [379] => [380] => == See also == [381] => * {{Annotated link|Cosmogony}} [382] => * {{Annotated link|Outline of astronomy}} [383] => * {{Annotated link|Outline of space science}} [384] => * {{Annotated link|Space exploration}} [385] => [386] => === Lists === [387] => * {{Annotated link|Glossary of astronomy}} [388] => * {{Annotated link|List of astronomical instruments}} [389] => * {{Annotated link|List of astronomical observatories}} [390] => * {{Annotated link|List of astronomy acronyms}} [391] => * {{Annotated link|List of software for astronomy research and education}} [392] => [393] => == References == [394] => {{Reflist}} [395] => [396] => == Bibliography == [397] => * {{Cite EB1911|wstitle= Astronomy | volume= 2 |last1= Newcomb |first1= Simon |author1-link= Simon Newcomb ||last2= Clerke |first2= Agnes Mary |author2-link= Agnes Mary Clerke | pages = 800–819 |short=1}} [398] => * {{cite book [399] => |last1 = Harpaz|first1 = Amos [400] => |title = Stellar Evolution [401] => |date= 1994|isbn = 978-1-56881-012-6|url = https://books.google.com/books?id=kd4VEZv8oo0C|publisher = A K Peters, Ltd}} [402] => * {{cite book|last=Unsöld|first=A.|title=The New Cosmos: An Introduction to Astronomy and Astrophysics|date=2001|publisher=Springer|isbn=978-3-540-67877-9|author2=Baschek, B.}} [403] => * {{cite book|last=James|first=C. Renée|title=Things That Go Bump in the Universe: How Astronomers Decode Cosmic Chaos |date=2023|url=https://www.nytimes.com/2023/12/13/books/review/things-that-go-bump-in-the-universe-c-renee-james.html|url-status=live |archiveurl=https://archive.today/20231213151825/https://www.nytimes.com/2023/12/13/books/review/things-that-go-bump-in-the-universe-c-renee-james.html|archivedate=13 Dec 2023|publisher=Johns Hopkins University Press|isbn=978-1421446936}} [404] => [405] => == External links == [406] => {{Commons}} [407] => {{Wikibooks}} [408] => [409] => * [http://ned.ipac.caltech.edu/ NASA/IPAC Extragalactic Database (NED)] ([http://ned.ipac.caltech.edu/Library/Distances/ NED-Distances]) [410] => * [http://ads.harvard.edu/books/clab/ Core books] and [http://ads.harvard.edu/books/claj/ Core journals] in Astronomy, from the Smithsonian/NASA [[Astrophysics Data System]] [411] => [412] => {{Astronomy navbox|state=uncollapsed}} [413] => {{Astronomy subfields|state=uncollapsed}} [414] => {{Natural science}} [415] => {{Solar System}} [416] => {{Glossaries of science and engineering}} [417] => {{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}} [418] => {{Authority control}} [419] => {{Use dmy dates|date=April 2019}} [420] => [421] => [[Category:Astronomy| ]] [] => )
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Astronomy

Astronomy is a natural science that studies celestial objects, such as stars, planets, comets, and galaxies, as well as the phenomena and processes that occur in outer space. It is one of the oldest sciences, dating back thousands of years, and has played a vital role in our understanding of the universe.

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It is one of the oldest sciences, dating back thousands of years, and has played a vital role in our understanding of the universe. This Wikipedia page provides a comprehensive overview of astronomy, covering its history, methods of observation, theoretical models, and significant discoveries. It explores the various branches of astronomy, including observational astronomy, theoretical astrophysics, and planetary science. The page also delves into the different tools and instruments used in astronomy, from telescopes to space probes, and explains the principles behind their functioning. Moreover, the article discusses important theories and concepts in astronomy, such as the Big Bang theory, stellar evolution, black holes, galaxy formation, and the search for extraterrestrial life. It highlights the contributions made by renowned astronomers throughout history, including names like Galileo Galilei, Isaac Newton, and Edwin Hubble. The page also discusses how astronomy has been aided by advancements in technology and data analysis methods, leading to significant breakthroughs in our understanding of the universe. In addition to its scientific pursuits, the article touches upon the cultural and historical significance of astronomy. It explores how ancient civilizations used astrology, a predecessor to modern astronomy, for navigation, timekeeping, and understanding natural phenomena. The page also provides information on major astronomical organizations, space agencies, and significant astronomical observatories around the world. Overall, this Wikipedia page offers a comprehensive and accessible resource for anyone seeking information on the fascinating field of astronomy, allowing readers to explore the vastness of the universe and the cutting-edge research conducted by astronomers worldwide.

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