Astronomy

{{Short description |Scientific study of celestial objects}} {{Hatnote group |{{About-distinguish-text |the scientific study of celestial objects |Astrology, a divinatory pseudoscience}}{{Other uses}}}} {{Good article}} {{pp-semi-indef}} {{pp-move}} {{CS1 config |mode=cs1}}

{{multiple image | perrow = 3 | total_width = 370 | image1 = Titan in front of the ring and Saturn.jpg | image2 = BD-08 1203 imaged by Euclid Space Telescope.png | image3 = Solar eclipse 1999 4.jpg | image4 = Laser Towards Milky Ways Centre.jpg | image5 = Black hole - Messier 87 crop max res.jpg | image6 = Hubble Interacting Galaxy UGC 9618 (2008-04-24).jpg | image7 = Cropped frame of the Constrained Local Universe Evolution Simulation (CLUES).jpg | image8 = Rho Ophiuchi (NIRCam Image) (2023-128).png | image9 = ASTRONAUT WHITE, EDWARD H. II - GEMINI-IV - EXTRAVEHICULAR ACTIVITY (EVA).jpg | footer = Nine images relating to astronomy.{{efn| Below is the list of the images present in the collage and their respective astronomy discipline(s), rightwards across the rows:

; Planetary science : Titan passing in front of Saturn in a natural‑colour mosaic from the Cassini spacecraft, showing atmospheric seasonal changes and the shadow of Saturn’s rings. ; Stellar astronomy : the star BD−08 1203 imaged by the Euclid Space Telescope, part of a deep stellar field used for photometric and astrometric studies. ; Solar physics : a photograph of the 1999 total solar eclipse in France, revealing the solar corona during totality. ; Observational astronomy & Galactic astronomy : the VLT at Paranal Observatory projecting a laser guide star into the mesosphere to enable adaptive optics observations of the Galactic Center. ; Astrophysics : the first direct image of the supermassive black hole M87* from the Event Horizon Telescope, showing the photon ring surrounding its shadow. ; Extragalactic astronomy : interacting spiral galaxies UGC 9618 (also known as VV 340 / Arp 302), imaged by the Hubble Space Telescope, illustrating early‑stage galactic merging. ; Cosmology & Computational astronomy : a frame from the CLUES project, depicting the large‑scale cosmic web of filaments, clusters and voids in the Universe. ; Astrochemistry : the Rho Ophiuchi cloud complex imaged by the JWST (NIRCam), showing jets from young stars, molecular hydrogen emission, and polycyclic aromatic hydrocarbons. ; Astrobiology : an EVA by astronaut Edward H. White II during Gemini 4, illustrating human presence in the outermost region of Earth’s biosphere and the study of life in space environments.

<br> These are just some of the many branches of astronomy. Others include (but are not limited to): high‑energy astrophysics, astroparticle physics, planetary geology, helioseismology, neutrino astronomy, astrostatistics and more. Also, there is often much overlap between the fields of astronomy, making the examples listed mostly conceptual and meant for conveying the focus of each mentioned. }} }}

'''Astronomy''' is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is the branch of astronomy that studies the universe as a whole.

Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptians, Babylonians, Greeks, Indians, Chinese, 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 calendars.

Astronomy is one of the few sciences in which amateurs play an active role. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.

==Etymology==

''Astronomy'' (from the Greek ἀστρονομία from ἄστρον ''astron'', "star" and -νομία ''-nomia'' from νόμος ''nomos'', "law" or "rule") means study of celestial objects.<ref>{{cite web |title=astronomy (n.) |url=https://www.etymonline.com/word/astronomy |publisher=Online Etymology Dictionary |access-date=13 August 2025}}</ref> Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. The two fields share a common origin but became distinct, astronomy being supported by physics while astrology is not.<ref>{{cite journal |bibcode=2012JAHH...15...42L |title='Astronomy' or 'astrology': A brief history of an apparent confusion |last=Losev |first=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 |issn=1440-2807}}</ref>

===Use of terms "astronomy" and "astrophysics"===

"Astronomy" and "astrophysics" are broadly synonymous in modern usage.<ref name="scharrinhausen">{{cite web |url=https://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 }}</ref><ref name="odenwald">{{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 }}</ref><ref name="pennstateerie">{{cite web |title=School of Science-Astronomy and Astrophysics |website=Penn State Erie |date=July 18, 2005 |url=http://www.erie.psu.edu/academic/science/degrees/astronomy/astrophysics.htm |access-date=20 June 2007 |archive-url=https://web.archive.org/web/20071101100832/http://www.erie.psu.edu/academic/science/degrees/astronomy/astrophysics.htm |archive-date=1 November 2007}}</ref> In dictionary definitions, "astronomy" is "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties",<ref name="mw-astronomy">{{cite web |title=astronomy |work=Merriam-Webster Online |url=http://www.m-w.com/dictionary/astronomy |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}}</ref> while "astrophysics" is the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena".<ref name="mw-astrophysics">{{cite web |title=astrophysics |work=Merriam-Webster Online |url=http://www.m-w.com/dictionary/astrophysics |access-date=20 June 2007 |archive-date=21 September 2012 |archive-url=https://archive.today/20120921/http://www.m-w.com/dictionary/astrophysics |url-status=live}}</ref> Sometimes, as in the introduction of the introductory textbook ''The Physical Universe'' by Frank Shu, "astronomy" means the qualitative study of the subject, whereas "astrophysics" is the physics-oriented version of the subject.<ref name="shu1982">{{cite book |first=F.H. |last=Shu |chapter=Preface |title=The Physical Universe |publisher=University Science Books |date=1983 |location=Mill Valley, California |isbn=978-0-935702-05-7 |url-access=registration |url=https://archive.org/details/physicaluniverse00shuf}}</ref> Some fields, such as astrometry, are in this sense purely astronomy rather than also astrophysics. Research departments may use "astronomy" and "astrophysics" according to whether the department is historically affiliated with a physics department,<ref name="odenwald"/> and many professional astronomers have physics rather than astronomy degrees.<ref name="pennstateerie"/> Thus, in modern use, the two terms are often used interchangeably.<ref name="scharrinhausen"/>

==History==

===Pre-historic=== [[File:Megaliths Aswan Nubia museum.JPG|left|thumb|Megaliths from Nabta Playa, constructed by Neolithic populations,<ref>{{cite book |last1=Ehret |first1=Christopher |url=https://books.google.com/books?id=Q5KjEAAAQBAJ |title=Ancient Africa: A Global History, to 300 CE |date=20 June 2023 |publisher=Princeton University Press |isbn=978-0-691-24409-9 |page=107 |language=en}}</ref> located in Aswan, Upper Egypt.<ref name="ReferenceC">{{cite book |last1=Holl |first1=Augustin |title=General history of Africa, IX: General history of Africa revisited |pages=469, 705–722|url=https://unesdoc.unesco.org/ark:/48223/pf0000396045?posInSet=1&queryId=N-EXPLORE-612fe50c-9ec6-4256-8bd3-7b7ec50033a7}}</ref>]] [[File:1600 Himmelsscheibe von Nebra sky disk anagoria.jpg|thumb|The Nebra sky disc found on Mittenberg hill in Germany and dated to {{circa |1800–1600 BCE}}.<ref>{{Cite journal |last=Pernicka |first=Ernst |last2=Adam |first2=Jörg |last3=Borg |first3=Gregor |last4=Brügmann |first4=Gerhard |last5=Bunnefeld |first5=Jan-Heinrich |last6=Kainz |first6=Wolfgang |last7=Klamm |first7=Mechthild |last8=Koiki |first8=Thomas |last9=Meller |first9=Harald |last10=Schwarz |first10=Ralf |last11=Stöllner |first11=Thomas |last12=Wunderlich |first12=Christian-Heinrich |last13=Reichenberger |first13=Alfred |date=2020 |title=Why the Nebra Sky Disc Dates to the Early Bronze Age. An Overview of the Interdisciplinary Results |url=https://www.jstor.org/stable/27045107 |journal=Archaeologia Austriaca |volume=104 |pages=89–122 |issn=0003-8008}}</ref> ]] The initial development of astronomy was driven by practical needs like agricultural calendars. Before recorded history archeological sites such as Stonehenge provide evidence of ancient interest in astronomical observations.<ref name=Ryden-2020>{{Cite book |last1=Ryden |first1=Barbara |url=https://www.cambridge.org/core/product/identifier/9781108933001/type/book |title=Foundations of Astrophysics |last2=Peterson |first2=Bradley M. |date=2020-08-27 |publisher=Cambridge University Press |isbn=978-1-108-93300-1 |edition=1 |doi=10.1017/9781108933001.002}}</ref>{{rp|15}} Evidence also comes from artefacts such as the Nebra sky disc inlaid with symbols interpreted as a sun, moon, and stars including a cluster of seven stars.<ref name="Meller 2021">{{cite book |url=https://www.academia.edu/80363367 |title=Time is power. Who makes time?: 13th Archaeological Conference of Central Germany |chapter=The Nebra Sky Disc – astronomy and time determination as a source of power |last=Meller |first=Harald |date=2021 |publisher=Landesmuseum für Vorgeschichte Halle (Saale). |isbn=978-3-948618-22-3}}</ref><ref name="Halle">{{cite web|url=https://www.landesmuseum-vorgeschichte.de/en/nebra-sky-disc.html |title=Nebra Sky Disc|website=Halle State Museum of Prehistory}}</ref><ref>{{cite web|url=https://the-past.com/feature/the-nebra-sky-disc-decoding-a-prehistoric-vision-of-the-cosmos/|title=The Nebra Sky Disc: decoding a prehistoric vision of the cosmos|website=The-Past.com|date=May 2022}}</ref> Megalithic structures located in Nabta Playa, Upper Egypt featured astronomical calendar arrangements in alignment with the heliacal rising of Sirius and supported calibration the yearly calendar for the annual Nile flood.<ref>{{cite book |last1=Ehret |first1=Christopher |title=Ancient Africa: A Global History, to 300 CE |date=20 June 2023 |publisher=Princeton University Press |isbn=978-0-691-24410-5 |pages=107–110 |url=https://books.google.com/books?id=S5KjEAAAQBAJ&q=christopher+ehret+nabta+playa |language=en}}</ref>

===Classical===

[[File:Ct-33-planisphere.jpg|thumb|left|A Babylonian planisphere (7th century BCE) was an early astronomical instrument. Its use of sexagesimals (e.g. 12, 24, 60, 360) is still being used today through having been broadly adopted for timekeeping and astrometry.<ref name="x754">{{cite web |last=Gent |first=R.H. van |title=Bibliography of Babylonian Astronomy & Astrology |website=science.uu.nl project csg |url=https://webspace.science.uu.nl/~gent0113/babylon/babybibl.htm |access-date=2024-11-22}}</ref>]]

Civilizations such as Egypt, Mesopotamia, Greece, India, China independently but with cross-cultural influences created astronomical observatories and developed ideas on the nature of the Universe, along with calendars and astronomical instruments.<ref name="Sarma 2000">{{cite journal |last=Sarma |first=Nataraja |title=Diffusion of astronomy in the ancient world |journal=Endeavour |volume=24 |issue=4 |date=2000 |doi=10.1016/S0160-9327(00)01327-2 |pages=157–164 |pmid=11196987 |url=https://linkinghub.elsevier.com/retrieve/pii/S0160932700013272|url-access=subscription }}</ref> A key early development was the beginning of mathematical and scientific astronomy among the Babylonians, laying the foundations for astronomical traditions in other civilizations.<ref>{{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 }}</ref> The Babylonians discovered that lunar eclipses recurred in the saros cycle of 223 synodic months.<ref>{{cite web |title=Eclipses and the Saros |publisher=NASA |url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |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 }}</ref>

Following the Babylonians, significant advances were made in ancient Greece and the Hellenistic world. Greek astronomy sought a rational, physical explanation for celestial phenomena.<ref>{{cite encyclopedia |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}}</ref> In the 4th century BC, Heracleides Ponticus was the first to proposed that the Earth rotates on its own axis.<ref>{{Cite news |title=Heracleides Ponticus {{!}} Biography & Facts {{!}} Britannica |url=https://www.britannica.com/biography/Heracleides-Ponticus |archive-url=http://web.archive.org/web/20251015114554/https://www.britannica.com/biography/Heracleides-Ponticus |archive-date=2025-10-15 |access-date=2026-01-25 |work=Encyclopedia Britannica |language=en}}</ref> In the 3rd century BC, Aristarchus of Samos estimated the 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 heliocentric model.<ref>{{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 }}</ref> In the 2nd century BC, Hipparchus calculated the size and distance of the Moon and invented the earliest known astronomical devices such as the astrolabe.<ref>{{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 |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}}</ref> He also observed the small drift in the positions of the equinoxes and solstices with respect to the fixed stars that we now know is caused by precession.<ref name="Ryden-2020" /> Hipparchus also created a catalog of 1020 stars, and most of the constellations of the northern hemisphere derive from Greek astronomy.<ref>{{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}}</ref> 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 clocks appeared in Europe.<ref name="insearchoflosttime">{{cite journal |last1=Marchant |first1=Jo |title=In search of lost time |journal=Nature |volume=444 |issue=7119 |pages=534–538 |date=2006 |pmid=17136067 |doi=10.1038/444534a |bibcode=2006Natur.444..534M |doi-access=free}}</ref>

===Post-classical=== After the classical Greek era, astronomy was dominated by the geocentric model of the Universe, or the Ptolemaic system, named after Claudius Ptolemy. His 13-volume astronomy work, named the ''Almagest'' in its Arabic translation, became the primary reference for over a thousand years.<ref name="Christian-2010">{{Cite book |title=A Question and Answer Guide to Astronomy |chapter-url=https://www.cambridge.org/core/books/question-and-answer-guide-to-astronomy/history-of-astronomy/228E94E3DBEEA10CC8D6DDCBFB738FED |chapter=History of astronomy |date=2010 |publisher=Cambridge University Press |isbn=978-0-511-67612-3 |editor-last=Christian |editor-first=Carol |location=Cambridge |pages=193–208 |doi=10.1017/cbo9780511676123.009 |editor-last2=Roy |editor-first2=Jean-René |editor-last3=Bely |editor-first3=Pierre-Yves}}</ref>{{rp|196}} In this system, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it.<ref>{{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}}</ref> While the system would eventually be discredited, it gave the most accurate predictions for the positions of astronomical bodies available at that time.<ref name="Christian-2010" />

With the arrival of Hellenistic astronomy in India through trade and cultural contacts, Indian astronomy entered a new phase during the early centuries CE.<ref>Pierre Cambon, Jean-François Jarrige. "Afghanistan, les trésors retrouvés: Collections du Musée national de Kaboul". Éditions de la Réunion des musées nationaux, 2006 – 297 pages. p. 269 [https://books.google.com/books?id=xJFtQgAACAAJ&q=afghanistan,+les+tresors+retrouves] "Les influences de l'astronomie grecques sur l'astronomie indienne auraient pu commencer de se manifester plus tot qu'on ne le pensait, des l'epoque Hellenistique en fait, par l'intermediaire des colonies grecques des Greco-Bactriens et Indo-Grecs" (French) Afghanistan, les trésors retrouvés", p. 269. Translation: "The influence of Greek astronomy on Indian astronomy may have taken place earlier than thought, as soon as the Hellenistic period, through the agency of the Greek colonies of the Greco-Bactrians and the Indo-Greeks.</ref> Earlier indigenous traditions, such as those recorded in the Vedāṅga Jyotiṣa, provided calendrical foundations, while Greek astronomical models were later integrated by scholars including Āryabhaṭa, Varāhamihira, and Brahmagupta.<ref name="Pingree (1978), 533, 554f.">D. Pingree: "History of Mathematical Astronomy in India", ''Dictionary of Scientific Biography'', Vol. 15 (1978), pp. 533–633 (533, 554f.)</ref> Āryabhaṭa notably improved methods for calculating planetary motions and eclipses.<ref>{{MacTutor|id=Aryabhata_I |title=Aryabhata the Elder}}</ref> In the later medieval period, the Kerala school contributed to astronomy through refined observational practices and more accurate planetary and eclipse calculations.<ref>{{MacTutor|id=Nilakantha |title=Nilakantha}}</ref>

[[File:Al- Fargānī, Aḥmad ibn Muḥammad – Compilatio astronomica, 1493 – BEIC 13262685.jpg |thumb |upright |Portrait of Alfraganus in the ''Compilatio astronomica'', 1493. Islamic astronomers collected and translated Indian, Persian and Greek texts, adding their own work.<ref name="n063">{{cite web |last=Akerman |first=Iain |title=The language of the stars |website=WIRED Middle East |date=2023-05-17 |url=https://wired.me/culture/arab-astronomy-the-language-of-stars/ |access-date=2024-11-23}}</ref>]]

Astronomy flourished in the medieval Islamic world. Astronomical observatories were established there by the early 9th century.<ref name="Kennedy-1962">{{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 |volume=53 |issue=2 |pages=237–39 |doi=10.1086/349558 }}</ref><ref name="Micheau-992-3">{{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}}</ref><ref>{{cite book |last=Nas |first=Peter J |title=Urban Symbolism |date=1993 |publisher=Brill Academic Publishers |isbn=978-90-04-09855-8 |page=350}}</ref> 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''.<ref name="NSOG">{{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}}</ref> The SN 1006 supernova, the brightest apparent magnitude stellar event in the last 1000 years, was observed by the Egyptian Arabic astronomer Ali ibn Ridwan and Chinese astronomers in 1006.<ref>{{cite book |last1=Murdin |first1=Paul |title=Supernovae |last2=Murdin |first2=Lesley |date=1985 |publisher=Cambridge University Press |isbn=978-0-521-30038-4 |edition=2 |location=Cambridge |page=14}}</ref> Iranian scholar Al-Biruni observed that, contrary to Ptolemy, the Sun's apogee (highest point in the heavens) was mobile, not fixed.<ref name="Goldstein1967">{{cite journal |title=The Arabic version of Ptolemy's planetary hypothesis |first=Bernard R. |last=Goldstein |page=6 |journal=Transactions of the American Philosophical Society |date=1967 |volume=57 |issue=pt. 4 |doi=10.2307/1006040 |jstor=1006040}}</ref><ref>{{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 }}</ref> Arabic astronomers introduced many Arabic names now used for individual stars.<ref>{{cite book | last1=Morrison | first1=Robert G. | chapter-url=https://link.springer.com/referenceworkentry/10.1007/978-1-4020-8265-8_89 | doi=10.1007/978-1-4020-8265-8_89 | chapter=Astronomy in Islam | title=Encyclopedia of Sciences and Religions | date=2013 | pages=155–158 | isbn=978-1-4020-8264-1 }}</ref>

The ruins at Great Zimbabwe and Timbuktu<ref>{{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}}</ref> may have housed astronomical observatories.<ref>{{cite magazine |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 |magazine=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}}</ref> In Post-classical West Africa, astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens and diagrams of orbits of the other planets based on complex mathematical calculations.<ref>{{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}}</ref> Songhai historian Mahmud Kati documented a meteor shower in 1583.<ref>{{cite book |last=Holbrook |first=Jarita C. |url=https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182 |title=African Cultural Astronomy |author2=Medupe, R. Thebe |author3=Johnson Urama |date=2008 |publisher=Springer |page=182 |isbn=978-1-4020-6638-2 |access-date=19 October 2020 |archive-url=https://web.archive.org/web/20210817020340/https://books.google.com/books?id=4DJpDW6IAukC&pg=PA182 |archive-date=17 August 2021 |url-status=live}}</ref>

In medieval Europe, Richard of Wallingford (1292–1336) invented the first astronomical clock, the Rectangulus which allowed for the measurement of angles between planets and other astronomical bodies,<ref name="Gimpel 1992">{{cite book |title=The Medieval Machine |first=Jean |last=Gimpel |author-link=Jean Gimpel |year=1992 |orig-date=1976 |edition=2nd |publisher=Pimlico |isbn=978-0-7126-5484-5 |pages=155–157}}</ref> as well as an equatorium called the ''Albion'' which could be used for astronomical calculations such as lunar, solar and planetary longitudes.<ref>{{cite book |last=Hannam |first=James |title=God's philosophers: how the medieval world laid the foundations of modern science |publisher=Icon Books |year=2009 |page=180}}</ref> Nicole Oresme (1320–1382) discussed evidence for the rotation of the Earth.<ref>Grant, ''The Foundations of Modern Science in the Middle Ages'', (Cambridge: Cambridge University Press, 1996), pp. 114–116.</ref> Jean Buridan (1300–1361) developed the theory of impetus, describing motions including of the celestial bodies.<ref>''Questions on the Eight Books of the Physics of Aristotle: Book VIII Question 12''. English translation in Clagett's 1959 ''Science of Mechanics in the Middle Ages '', p. 536</ref><ref>{{cite web |last1=Van Dyck |first1=Maarten |last2=Malara |first2=Ivan |title=Renaissance Concept of Impetus |url=https://philarchive.org/archive/VANRCO-3 |access-date=12 August 2025}}</ref> 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 for Easter.<ref>{{cite book |last=Heilbron |first=J.L. |title=The Sun in the Church: Cathedrals as Solar Observatories |year=1999 |publisher=Harvard University Press |page=3}}</ref>

===Copernicus=== During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the solar system.<ref>{{harvnb |Forbes |1909 |loc=Book 2, chapter 4: The Reign of Epicycles—From Ptolemy to Copernicus}}</ref> While his model maintained circular orbits, it was sufficient to calculate the size of planetary orbits and their period. The appealing simplicity of Copernican astronomy led to its adoption among astronomers even before it was confirmed by Galileo's telescopic observations in the 1600s.<ref name=Ryden-2020/>{{rp|40}}

===Early telescopic===

[[File:Galileo's sketches of the moon.png |thumb |upright |The first sketches of the Moon's topography, from Galileo's ground-breaking ''Sidereus Nuncius'' (1610)]] Sometime around 1608 the telescope was invented and by 1610, Galileo Galilei observed phases on the planet Venus similar to those of the Moon, supporting the heliocentric model.<ref name=Ryden-2020/> Around the same time the heliocentric model was organized quantitatively by Johannes Kepler.<ref>{{harvnb |Forbes |1909 |loc=Book 2, chapter 6: Galileo and the Telescope—Notionsl of gravity by Horrocks, etc.}}</ref> Analyzing two decades of careful observations by Tycho Brahe, Kepler devised a system that described the details of the motion of the planets around the Sun.<ref name=Longair-2023>{{Cite book |last=Longair |first=Malcolm S. |url=https://link.springer.com/10.1007/978-3-662-65891-8_1 |title=Galaxy Formation |date=2023 |publisher=Springer Berlin Heidelberg |isbn=978-3-662-65890-1 |location=Berlin, Heidelberg |pages=3–30 |language=en |doi=10.1007/978-3-662-65891-8_1}}</ref>{{rp|4}}<ref>{{Cite book |last1=Caspar |first1=Max |title=Kepler |last2=Hellman |first2=Clarisse Doris |author-link2=C. Doris Hellman |date=1993 |publisher=Dover Publications |isbn=978-0-486-67605-0 |location=New York}}</ref> While Kepler discarded the uniform circular motion of Copernicus in favor of elliptical motion,<ref name=Ryden-2020/> he did not succeed in formulating a theory behind the laws he wrote down.<ref>{{harvnb |Forbes |1909 |loc=Book 2, chapter 5: Discovery of the True Solar System—Tycho Brahe—Kepler}}</ref> It was Isaac Newton, with his invention of celestial dynamics and his law of gravitation, who finally explained the motions of the planets.<ref name="f58-64">{{harvnb |Forbes |1909 |loc=Book 2, chapter 7: Sir Isaac Newton—Law of Universal Gravitation}}</ref> Newton also developed the reflecting telescope.<ref>{{harvnb |Forbes |1909 |loc=Book 3, chapter 10: History of the Telescope—Spectroscope}}</ref> Newton, in collaboration with Richard Bentley proposed that stars are like the Sun only much further away.<ref name=Longair-2023/>

The new telescopes also altered ideas about stars. By 1610 Galileo discovered that the band of light crossing the sky at night that we call the Milky Way was composed of numerous stars.<ref name=Ryden-2020/>{{rp|48}} In 1668 James Gregory compared the luminosity of Jupiter to Sirius to estimate its distance at over 83,000 AU.<ref name=Longair-2023/> The English astronomer John Flamsteed, Britain's first Astronomer Royal, catalogued over 3000 stars but the data were published against his wishes in 1712.<ref name="RMG Flamsteed">{{cite web |title=Who was John Flamsteed, the first Astronomer Royal? |url=https://www.rmg.co.uk/stories/space-astronomy/who-was-john-flamsteed-first-astronomer-royal |publisher=Royal Museums Greenwich |access-date=12 August 2025}}</ref> The astronomer William Herschel made a detailed catalog of nebulosity and clusters, and in 1781 discovered the planet Uranus, the first new planet found.<ref>{{harvnb |Forbes |1909 |loc=Book 2, chapter 9: Discovery of New Planets—Herschel, Piazzi, Adams, and Le Verrier}}</ref> Friedrich Bessel developed the technique of stellar parallax in 1838 but it was so difficult to apply that only about 100 stars were measured by 1900.<ref name=Longair-2023/>

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.<ref>{{harvnb |Forbes |1909 |loc=Book 2, chapter 8: Newton's Successors—Halley, Euler, Lagrange, Laplace, etc.}}</ref>

Significant advances in astronomy came about with the introduction of new technology, including the spectroscope and astrophotography. In 1814–15, Joseph von Fraunhofer discovered some 574 dark lines in the spectrum of the sun and of other stars.<ref name="Ferguson Maciaszek 2014">{{cite web |title=The Glassmaker Who Sparked Astrophysics |last1=Ferguson |first1=Kitty |last2=Maciaszek |first2=Miko |url=http://nautil.us/issue/11/light/the-glassmaker-who-sparked-astrophysics |date=20 March 2014 |access-date=8 April 2018 |publisher=Nautilus |archive-date=23 March 2014 |archive-url=https://web.archive.org/web/20140323010729/http://nautil.us/issue/11/light/the-glassmaker-who-sparked-astrophysics }}</ref><ref>{{cite magazine |last1=Buehrke |first1=Thomas |title=Physics & Astronomy: Cosmic Detective Work |magazine=Max Planck Research |date=2021 |issue=4 |pages=67–72 |url=https://www.mpg.de/18487049/W004_Physics_Astronomy_066-072.pdf}}</ref> In 1859, Gustav Kirchhoff ascribed these lines to the presence of different elements.<ref>{{cite journal |first=G. |last=Kirchhoff |title=Ueber die Fraunhofer'schen Linien |language=de |trans-title=On Fraunhofer's Lines |journal=Annalen der Physik |volume=185 |issue=1 |pages=148–150 |date=1860 |doi=10.1002/andp.18601850115 |bibcode=1860AnP...185..148K |url=https://zenodo.org/record/1423666 }}</ref>

===Galaxies===

thumb|upright=1.25|Diagram of the stars, from William Herschel's ''On the construction of the heavens''.<ref>{{Cite journal |last1=Herschel |first1=William |date=1785-12-31 |title=On the construction of the heavens |journal=Philosophical Transactions of the Royal Society of London |language=en |volume=75 |pages=213–266 |doi=10.1098/rstl.1785.0012 |doi-access=free |issn=0261-0523 |bibcode=1785RSPT...75..213H }}</ref>

In the late 1700s William Herschel mapped the distribution of stars in different directions from Earth, concluding that the universe consisted of the Sun near the center of disk of stars, the Milky Way. After John Michell demonstrated that stars differ in intrinsic luminosity and after Herschel's own observations with more powerful telescopes that additional stars appeared in all directions, astronomers began to consider that some of the fuzzy spiral nebulae were distant ''island Universes''.<ref name=Longair-2023/>{{rp|6}}

[[File:Andromeda_Nebula_-_Isaac_Roberts,_29_December_1888 (cropped).jpg |thumb |upright |Photograph of the Great Andromeda "Nebula" by Isaac Roberts in 1888.<ref>{{cite journal |last1=James |first1=S. H. G. |title=DR Isaac Roberts (1829-1904) and his observatories |journal=Journal of the British Astronomical Association |date=1993 |volume=103 |page=120 |bibcode=1993JBAA..103..120J }}</ref><ref>{{Cite book |last=Roberts |first=Isaac |url=https://www.cambridge.org/core/product/identifier/9780511659119/type/book |title=Photographs of Stars, Star-Clusters and Nebulae: Together with Records of Results Obtained in the Pursuit of Celestial Photography |date=2010-10-31 |publisher=Cambridge University Press |isbn=978-1-108-01523-3 |edition=1 |doi=10.1017/cbo9780511659119}}</ref>{{rp|63}}]]

The existence of galaxies, including the Earth's galaxy, the Milky Way, as a group of stars was only demonstrated in the 20th century.<ref name=Belkora2003>{{cite book |last=Belkora |first=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}}</ref> In 1912, Henrietta Leavitt discovered Cepheid variable stars with well-defined, periodic luminosity changes which can be used to fix the star's true luminosity which then becomes an accurate tool for distance estimates. Using Cepheid variable stars, Harlow Shapley constructed the first accurate map of the Milky Way.<ref name=Longair-2023/>{{rp|7}} Using the Hooker Telescope, Edwin Hubble identified Cepheid variables in several spiral nebulae and in 1922–1923 proved conclusively that Andromeda Nebula and Triangulum among others, were entire galaxies outside our own, thus proving that the universe consists of a multitude of galaxies.<ref name="SharovNovikov1993">{{cite book |last1=Sharov |first1=Aleksandr Sergeevich |last2=Novikov |first2=Igor Dmitrievich |title=Edwin Hubble, the discoverer of the big bang universe |url=https://books.google.com/books?id=ttEwkEdPc70C&pg=PA34 |access-date=December 31, 2011 |date=1993 |publisher=Cambridge University Press |isbn=978-0-521-41617-7 |page=34 |archive-date=June 23, 2013 |archive-url=https://web.archive.org/web/20130623075250/http://books.google.com/books?id=ttEwkEdPc70C&pg=PA34 |url-status=live}}</ref>

=== Cosmology === {{main|History of physical cosmology}}

Albert Einstein's 1917 publication of general relativity began the modern era of theoretical models of the universe as a whole.<ref>{{Cite book |last=Kragh |first=Helge S. |url=https://academic.oup.com/book/12815 |title=Conceptions of Cosmos |date=2006-12-07 |publisher=Oxford University Press |isbn=978-0-19-920916-3 |language=en |doi=10.1093/acprof:oso/9780199209163.001.0001}}</ref> In 1922, Alexander Friedman published simplified models for the universe showing static, expanding and contracting solutions.<ref name=Longair-2023/>{{rp|13}} In 1929 Hubble published observations that the galaxies are all moving away from Earth with a velocity proportional to distance, a relation now known as Hubble's law. This relation is expected if the universe is expanding.<ref name=Longair-2023/>{{rp|13}} The consequence that the universe was once very dense and hot, a Big Bang concept expounded by Georges Lemaître in 1927,<ref>{{cite journal |last1=Nussbaumer |first1=H. |last2=Bieri |first2=L. |author2-link=Lydia Bieri |date=2011 |title=Who discovered the expanding universe? |journal=The Observatory |volume=131 |issue=6 |pages=394–398 |arxiv=1107.2281 |bibcode=2011Obs...131..394N }}</ref> was discussed but no experimental evidence was available to support it. From the 1940s on, nuclear reaction rates under high density conditions were studied leading to the development of a successful model of big bang nucleosynthesis in the late 1940s and early 1950s. Then in 1965 cosmic microwave background radiation was discovered, cementing the evidence for the Big Bang.<ref name=Longair-2023/>{{rp|16}}

Astrophysics predicted the existence of objects such as black holes<ref name="Oppenheimer Volkoff 1939">{{Cite journal |last1=Oppenheimer |first1=J. R. |author-link1=J. Robert Oppenheimer |last2=Volkoff |first2=G. M. |author-link2=George Volkoff |date=1939 |title=On Massive Neutron Cores |url=https://archive.org/details/sim_physical-review_1939-02-15_55_4/page/374 |journal=Physical Review |volume=55 |issue=4 |pages=374–381 |doi=10.1103/PhysRev.55.374 |bibcode=1939PhRv...55..374O}}</ref> and neutron stars.<ref>{{cite book |last1=Bird |first1=Kai |author-link=Kai Bird |first2=Martin J. |last2=Sherwin |author-link2=Martin J. Sherwin |title=American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer |location=New York |publisher=Alfred A. Knopf |year=2005 |isbn=978-0-375-41202-8 |url=https://archive.org/details/americanpromethe00bird/mode/2up |url-access=registration }}</ref>{{rp|89}}<ref>{{cite journal |journal=Physical Review |volume=46 |title=Remarks on Super-Novae and Cosmic Rays |issue=1 |last1=Baade |first1=Walter |author-link=Walter Baade |last2=Zwicky |first2=Fritz |author-link2=Fritz Zwicky |pages=76–77 |doi=10.1103/PhysRev.46.76.2 |date=1934 |bibcode=1934PhRv...46...76B |url=https://authors.library.caltech.edu/5999/1/BAApr34.pdf |access-date=2019-09-16 |archive-date=2021-02-24 |archive-url=https://web.archive.org/web/20210224205601/https://authors.library.caltech.edu/5999/1/BAApr34.pdf |url-status=live }}</ref> These have been used to explain phenomena such as quasars<ref name="Schmidt 1963">{{Cite journal |last=Schmidt |first=M. |author-link=Maarten Schmidt |date=March 1963 |title=3C 273: A Star-Like Object with Large Red-Shift |journal=Nature |volume=197 |issue=4872 |page=1040 |bibcode=1963Natur.197.1040S |doi=10.1038/1971040a0 |s2cid=4186361 |doi-access=free}}</ref> and pulsars.<ref name="Gold 1968">{{Cite journal |last1=Gold |first1=T. |title=Rotating Neutron Stars as the Origin of the Pulsating Radio Sources |journal=Nature |volume=218 |pages=731–732 |year=1968 |doi=10.1038/218731a0 |bibcode=1968Natur.218..731G |issue=5143|s2cid=4217682}}</ref>

Space telescopes have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.<ref>{{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 }}</ref> The LIGO project detected evidence of gravitational waves in 2015.<ref name="Discovery 2016">{{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 |doi-access=free }}</ref><ref name='Abbot'>{{cite journal |last=Abbott |first=B.P. |title=Observation of Gravitational Waves from a Binary Black Hole Merger |collaboration=LIGO Scientific Collaboration and Virgo Collaboration |journal=Physical Review Letters |year=2016 |volume=116 |issue=6 |article-number=061102 |doi=10.1103/PhysRevLett.116.061102 |pmid=26918975 |bibcode=2016PhRvL.116f1102A |arxiv=1602.03837 |s2cid=124959784}}</ref>

==Observational astronomy==

[[File:Openstax Astronomy EM spectrum and atmosphere.jpg |thumb |upright=1.6|center |Overview of types of observational astronomy, relating wavelengths and their observability]]

Observational astronomy relies on many different wavelengths of electromagnetic radiation and the forms of astronomy are categorized according to the corresponding region of the electromagnetic spectrum on which the observations are made.<ref>{{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 }}</ref> Specific information on these subfields is given below.

===Radio===

[[File:USA.NM.VeryLargeArray.02.jpg |thumb |The Very Large Array in New Mexico, a radio telescope ]]

Radio astronomy uses radiation with long wavelengths, mainly between 1 millimeter and 15 meters (frequencies from 20 MHz to 300 GHz), far outside the visible range.<ref name="RAL">{{cite web |title=What is radio astronomy |url=http://www.radioastrolab.it/en/radio-astronomy/what-is-radio-astronomy/ |publisher=RadioAstroLab |access-date=12 August 2025 |archive-url=https://archive.today/20130704122042/http://www.radioastrolab.it/en/radio-astronomy/what-is-radio-astronomy/ |archive-date=2013-07-04}}</ref> Hydrogen, otherwise an invisible gas, produces a spectral line at 21 cm (1420 MHz) which is observable at radio wavelengths.<ref name="SKAO">{{cite web |title=What is radio astronomy? |url=https://www.skao.int/en/resources/what-radio-astronomy |publisher=SKAO |access-date=13 August 2025 |date=2025}}</ref> Objects observable at radio wavelengths include interstellar gas,<ref name="SKAO"/> pulsars,<ref name="SKAO"/> fast radio bursts,<ref name="SKAO"/> supernovae,<ref>{{cite web |title=Radio Wave Emissions from Supernova 1987a |url=https://www.jpl.nasa.gov/news/radio-wave-emissions-from-supernova-1987a/ |publisher=Jet Propulsion Laboratory |access-date=13 August 2025 |date=March 11, 1987}}</ref> and active galactic nuclei.<ref name="Radcliffe Barthel Garrett 2021">{{cite journal |last1=Radcliffe |first1=J. F. |last2=Barthel |first2=P. D. |last3=Garrett |first3=M. A. |last4=Beswick |first4=R. J. |last5=Thomson |first5=A. P. |last6=Muxlow |first6=T. W. B. |title=The radio emission from active galactic nuclei |journal=Astronomy & Astrophysics |volume=649 |date=2021 |doi=10.1051/0004-6361/202140791 |doi-access=free |page=L9 |arxiv=2104.04519 |bibcode=2021A&A...649L...9R }}</ref>

===Infrared===

[[File:The Keck Subaru and Infrared obervatories.JPG |thumb |The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, both observatories that operate 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.]]

Infrared astronomy detects infrared radiation with wavelengths longer than red visible light, 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 disks 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 clouds and the cores of galaxies. Observations from the Wide-field Infrared Survey Explorer (WISE) have been particularly effective at unveiling numerous galactic protostars and their host star clusters.<ref name="wright">{{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}}</ref><ref name=ma2013>{{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}}</ref>

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.<ref>{{cite news |date=11 September 2003 |title=Why infrared astronomy is a hot topic |publisher=ESA |url=http://www.esa.int/esaCP/SEMX9PZO4HD_FeatureWeek_0.html |access-date=11 August 2008 |archive-date=30 July 2012 |archive-url=https://archive.today/20120730/http://www.esa.int/esaCP/SEMX9PZO4HD_FeatureWeek_0.html |url-status=live}}</ref> Some molecules radiate strongly in the infrared. This allows the study of the chemistry of space.<ref>{{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}}</ref>

The James Webb Space Telescope senses infrared radiation to detect very distant galaxies. Visible light from these galaxies was emitted billions of years ago and the expansion of the universe shifted the light in to the infrared range. By studying these distant galaxies astronomers hope to learn about the formation of the first galaxies.<ref>{{Cite journal |last1=Rieke |first1=Marcia J. |last2=Kelly |first2=Douglas |last3=Horner |first3=Scott |date=2005-08-18 |editor-last=Heaney |editor-first=James B. |editor2-last=Burriesci |editor2-first=Lawrence G. |title=Overview of James Webb Space Telescope and NIRCam's Role |url=https://ircamera.as.arizona.edu/nircam/pdfs/5904-1_Rieke.pdf |journal=Proc. SPIE 5904, Cryogenic Optical Systems and Instruments XI |series=Cryogenic Optical Systems and Instruments XI |volume=5904 |page=590401 |doi=10.1117/12.615554 |bibcode=2005SPIE.5904....1R }}</ref>

===Optical===

Historically, optical astronomy, which has been also called visible light astronomy, is the oldest form of astronomy.<ref name="moore1997">{{cite book |last1=Moore |first1=Patrick |title=Philip's atlas of the universe |date=2007 |publisher=Philip's |location=London |isbn=978-0-540-09118-8 |pages=20–21 |edition=6., new |chapter=Invisible Astronomy}}</ref> 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 devices (CCDs) and recorded on modern medium. Although visible light itself extends from approximately 380 to 700 nm<ref>{{cite web |title=Visible Light - NASA Science |url=https://science.nasa.gov/ems/09_visiblelight/ |website=NASA.gov |publisher=NASA |access-date=5 August 2025 |date=10 August 2016}}</ref> that same equipment can be used to observe some near-ultraviolet and near-infrared radiation.<ref>{{cite web |title=Glossary term: Optical Astronomy |url=https://astro4edu.org/resources/glossary/term/229/ |website=IAU Office of Astronomy for Education |publisher=International Astronomical Union |access-date=5 August 2025}}</ref>

===Ultraviolet===

Ultraviolet astronomy employs ultraviolet wavelengths which are absorbed by the Earth's atmosphere, requiring observations 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 OB stars that are very bright at these wavelengths.<ref>{{cite book |last=Mohammed |first=Steven Matthew |title=Probing the Ultraviolet Milky Way: The Final Galactic Puzzle Piece |date=2021 |publisher=Columbia University (PhD thesis) |pages=11–13 |doi=10.7916/d8-vqqh-qz10 |url=https://academiccommons.columbia.edu/doi/10.7916/d8-vqqh-qz10/download}}</ref>

===X-ray===

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

X-ray astronomy uses X-radiation, produced by extremely hot and high-energy processes. Since X-rays are absorbed by the Earth's atmosphere, observations must be performed at high altitude, such as from balloons, rockets, or specialized satellites. X-ray sources include X-ray binaries, supernova remnants, clusters of galaxies, and active galactic nuclei.<ref name="Arnaud 2007">{{cite web |last1=Arnaud |first1=Keith |title=An Introduction to X-ray Astronomy |url=https://heasarc.gsfc.nasa.gov/docs/xrayschool-2007/arnaud_intro.pdf |publisher=NASA |access-date=13 August 2025 |date=2007}}</ref> Since the Sun's surface is relatively cool, X-ray images of the Sun and other stars give valuable information on the hot solar corona.<ref>{{Cite journal |last=Godel |first=Manuel |date=2004 |title=X-ray astronomy of stellar coronae |url=http://link.springer.com/10.1007/s00159-004-0023-2 |journal=The Astronomy and Astrophysics Review |language=en |volume=12 |issue=2–3 |page=71 |doi=10.1007/s00159-004-0023-2 |arxiv=astro-ph/0406661 |bibcode=2004A&ARv..12...71G |issn=0935-4956}}</ref>

===Gamma-ray===

Gamma ray astronomy observes astronomical objects at the shortest wavelengths (highest energy) of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as the Compton Gamma Ray Observatory,<ref>{{cite web |url=http://imagine.gsfc.nasa.gov/docs/science/know_l1/history_gamma.html |archive-url=https://web.archive.org/web/19980520035819/http://imagine.gsfc.nasa.gov/docs/science/know_l1/history_gamma.html |archive-date=May 20, 1998 |title=The History of Gamma-ray Astronomy |publisher=NASA |access-date=November 14, 2010}}</ref> or by specialized telescopes called atmospheric Cherenkov telescopes. 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.<ref>{{cite web |title=MAGIC telescopes webpage |url=http://magic.mppmu.mpg.de/introduction/iact.html |access-date=2012-06-15 |archive-url=https://web.archive.org/web/20120511032953/http://magic.mppmu.mpg.de/introduction/iact.html|archive-date=2012-05-11}}</ref><ref name="spectrum">{{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}}</ref> Gamma-ray astronomy provides information on the origin of cosmic rays, possible annihilation events for dark matter, relativistic particles outflows from active galactic nuclei (AGN), and, using AGN as distant sources, properties of intergalactic space.<ref> {{Cite journal |last=Funk |first=Stefan |date=2015-10-19 |title=Ground- and Space-Based Gamma-Ray Astronomy |url=https://www.annualreviews.org/content/journals/10.1146/annurev-nucl-102014-022036 |journal=Annual Review of Nuclear and Particle Science |language=en |volume=65 |issue= |pages=245–277 |doi=10.1146/annurev-nucl-102014-022036 |arxiv=1508.05190 |bibcode=2015ARNPS..65..245F |issn=0163-8998}}</ref> Gamma-ray bursts, which radiate transiently, are extremely energetic events, and are the brightest (most luminous) phenomena in the universe.<ref>{{Cite journal |last1=Gehrels |first1=Neil |author-link=Neil Gehrels |last2=Mészáros |first2=Péter |author-link2=Péter Mészáros |date=2012-08-24 |title=Gamma-Ray Bursts |journal=Science |volume=337 |issue=6097 |pages=932–936 |doi=10.1126/science.1216793 |pmid=22923573 |arxiv=1208.6522 |bibcode=2012Sci...337..932G }}</ref>

===Non-electromagnetic observation===

[[File:Antares Neutrinoteleskop.jpg|thumb|The underground ANTARES neutrino telescope ]]

Some events originating from great distances may be observed from the Earth using systems that do not rely on electromagnetic radiation.<ref name="Gaisser 1990"/><ref name="Abbott 2016"/>

In neutrino astronomy, astronomers use heavily shielded underground facilities such as SAGE, GALLEX, and Kamioka II/III for the detection of neutrinos. The vast majority of the neutrinos streaming through the Earth originate from the Sun, but 24 neutrinos were also detected from supernova 1987A. Cosmic rays, 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.<ref name="Gaisser 1990">{{cite book |last=Gaisser |first=Thomas K. |date=1990 |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] |publisher=Cambridge University Press |isbn=978-0-521-33931-5}}</ref>

Gravitational-wave astronomy employs gravitational-wave detectors 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 detection on 14 September 2015, observing gravitational waves from a binary black hole.<ref name="Abbott 2016">{{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 |article-number=061102 |year=2016 |doi=10.1103/PhysRevLett.116.061102 |arxiv=1602.03837 |bibcode=2016PhRvL.116f1102A |pmid=26918975 |s2cid=124959784 }}</ref><ref>{{cite magazine |last1=Moskowitz |first1=Clara |title=Gravitational Waves Discovered from Colliding Black Holes |magazine=Scientific American |date=February 11, 2016 |url=https://www.scientificamerican.com/article/gravitational-waves-discovered-from-colliding-black-holes1/}}</ref> A second gravitational wave was detected on 26 December 2015 and additional observations should continue but gravitational waves require extremely sensitive instruments.<ref>{{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 }}</ref><ref>{{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 |article-number=241103 |doi=10.1103/PhysRevLett.116.241103 |pmid=27367379 |arxiv=1606.04855 |bibcode=2016PhRvL.116x1103A |s2cid=118651851 }}</ref>

The combination of observations made using electromagnetic radiation, neutrinos or gravitational waves and other complementary information, is known as multi-messenger astronomy.<ref>{{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}}</ref><ref>{{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 }}</ref>

===Astrometry and celestial mechanics===

[[File:Interferometric astrometry.svg|thumb|upright=1.3|Use of optical interferometry to determine precise positions of stars]]

One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects known as astrometry.<ref>{{Cite book |last1=Kovalevsky |first1=Jean |url=https://www.cambridge.org/core/product/identifier/9781139106832/type/book |title=Fundamentals of Astrometry |last2=Seidelmann |first2=P. Kenneth |date=2004-06-03 |publisher=Cambridge University Press |isbn=978-0-521-64216-3 |edition=1 |doi=10.1017/cbo9781139106832}}</ref> 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 calendars.<ref name=":0">{{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 |page=39}}</ref> Careful measurement of the positions of the planets has led to a solid understanding of gravitational perturbations, and an ability to determine past and future positions of the planets with great accuracy, a field known as celestial mechanics.<ref>{{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}}</ref> 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.<ref name="UWA cosmic distance ladder">{{cite web |title=Climbing the cosmic distance ladder |url=https://www.uwa.edu.au/study/-/media/Faculties/Science/Docs/Climbing-the-cosmic-distance-ladder.pdf |publisher=University of Western Australia |access-date=12 August 2025}}</ref> Measurements of the radial velocity<ref name="Lindegren2003">{{cite journal |last1=Lindegren |first1=Lennart |last2=Dravins |first2=Dainis |date=April 2003 |title=The fundamental definition of "radial velocity" |journal=Astronomy and Astrophysics |volume=401 |issue=3 |pages=1185–1201 |doi=10.1051/0004-6361:20030181 |bibcode=2003A&A...401.1185L |arxiv=astro-ph/0302522 |s2cid=16012160 }}</ref><ref>{{cite journal |first1=Dainis |last1=Dravins |first2=Lennart|last2=Lindegren |first3=Søren |last3=Madsen |year=1999 |journal=Astron. Astrophys. |volume=348 |pages=1040–1051|bibcode=1999A&A...348.1040D |title=Astrometric radial velocities. I. Non-spectroscopic methods for measuring stellar radial velocity |arxiv=astro-ph/9907145 }}</ref> and proper motion of stars allow astronomers to plot the movement of these systems through the Milky Way galaxy.<ref>{{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 }}</ref>

== Subfields by scale ==

=== Physical cosmology ===

[[File:Hubble Extreme Deep Field (full resolution).png |thumb |Hubble Extreme Deep Field]]

Physical cosmology, the study of large-scale structure of the Universe, seeks to understand the formation and evolution of the cosmos. Fundamental to modern cosmology is the well-accepted theory of the Big Bang, the concept that the universe begin extremely dense and hot, then expanded over the course of 13.8 billion years<ref>{{cite web |title=Cosmic Detectives |url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives |publisher=The European Space Agency (ESA) |date=2 April 2013 |access-date=15 April 2013 |archive-date=11 February 2019 |archive-url=https://web.archive.org/web/20190211204726/http://www.esa.int/Our_Activities/Space_Science/osmic_detectives |url-status=live}}</ref> to its present condition.<ref name=Dodelson2003/> The concept of the Big Bang became widely accepted after the discovery of the microwave background radiation in 1965.<ref name=Dodelson2003>{{cite book |last=Dodelson |first=Scott |title=Modern cosmology |date=2003 |isbn=978-0-12-219141-1 |publisher=Academic Press |pages=1–22}}</ref> Dark matter and dark energy are now thought form 96% of the mass of the Universe. For this reason, much effort is expended in trying to understand the physics of these components.<ref>{{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}}</ref>

=== Extragalactic ===

[[File:grav.lens1.arp.750pix.jpg |thumb |upright=0.8 |The blue, loop-shaped objects are multiple images of the same galaxy, duplicated by gravitational lensing. The cluster's gravitational field bends light, magnifying and distorting the image of a more distant object.]]

The study of objects outside our galaxy is concerned with the formation and evolution of galaxies, their morphology (description) and classification, the observation of active galaxies, and at a larger scale, the groups and clusters of galaxies. These assist the understanding of the large-scale structure of the cosmos.<ref name=":0"/>

===Galactic ===

Galactic astronomy studies galaxies including the Milky Way, a barred spiral galaxy that is a prominent member of the Local Group of galaxies and contains the Solar System. It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is within the dusty outer arms, large portions of the Milky Way are obscured from view.<ref name=":0"/>{{rp |pages=837–842, 944}}

Kinematic studies of matter in the Milky Way and other galaxies show 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.<ref>{{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}}</ref>

===Stellar ===

{{further|Star}}

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.<ref name=Amos7>Harpaz, 1994, pp. 7–18</ref> Aspects studied include star formation in giant molecular clouds; the formation of protostars; and the transition to nuclear fusion and main-sequence stars,<ref name=Smith2004>{{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}}</ref> carrying out nucleosynthesis.<ref name=Amos7/> Further processes studied include stellar evolution,<ref name=Amos>Harpaz, 1994, p. 20 and whole book</ref> ending either with supernovae<ref>Harpaz, 1994, pp. 173–78</ref> or white dwarfs. The ejection of the outer layers forms a planetary nebula.<ref>Harpaz, 1994, pp. 111–18</ref> 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.<ref>Harpaz, 1994, pp. 189–210</ref>

===Solar ===

[[File:Uvsun trace big.jpg |thumb |upright=0.8 |An ultraviolet image of the Sun's active photosphere as viewed by the NASA's TRACE space telescope.]]

Solar astronomy is the study of the Sun, a typical main-sequence dwarf star of stellar class G2 V, and about 4.6 billion years (Gyr) old. Processes studied by the science include the sunspot cycle,<ref name="solar FAQ">{{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}}</ref> the sun's changes in luminosity, both steady and periodic,<ref name="Environmental issues : essential primary sources.">{{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}}</ref><ref name="future-sun">{{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 }}</ref> and the behavior of the sun's various layers, namely its core with its nuclear fusion, the radiation zone, the convection zone, the photosphere, the chromosphere, and the corona.<ref name=":0"/>{{rp |pages=498–502}}

===Planetary science===

[[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 Martian atmosphere (comparable to a terrestrial tornado) created the long, dark streak.]]

Planetary science is the study of the assemblage of planets, moons, dwarf planets, comets, asteroids, and other bodies orbiting the Sun, as well as exoplanets orbiting distant stars. The Solar System has been relatively well-studied, initially through telescopes and then later by spacecraft.<ref name="geology">{{cite book |url=https://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 }}</ref><ref name="Montmerle2006">{{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}}</ref>

Processes studied include planetary differentiation; the generation of, and effects created by, a planetary magnetic field;<ref>Montmerle, 2006, pp. 87–90</ref> and the creation of heat within a planet, such as by collisions, radioactive decay, and tidal heating. In turn, that heat can drive geologic processes such as volcanism, tectonics, and surface erosion, studied by branches of geology.<ref name="new solar system">{{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=70 |edition=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}}</ref>

== Interdisciplinary subfields ==

=== Astrochemistry ===

Astrochemistry is an overlap of astronomy and chemistry. It studies the abundance and reactions of molecules in the Universe, and their interaction with radiation. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. Studies in this field contribute for example to the understanding of the formation of the Solar System.<ref>{{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}}</ref>

=== Astrobiology ===

Astrobiology (or exobiology<ref>[http://www.merriam-webster.com/dictionary/exobiology Merriam 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)</ref>) studies the origin of life and its development other than on earth. It considers whether extraterrestrial life exists, and how humans can detect it if it does.<ref name="about">{{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}}</ref> It makes use of astronomy, biochemistry, geology, microbiology, physics, and planetary science to investigate the possibility of life on other worlds and help recognize biospheres that might be different from that on Earth.<ref>{{cite web |title=Astrobiology |url=https://www.ucl.ac.uk/planetary-sciences/research/astrobiology |publisher=University College London |access-date=13 August 2025}}</ref> The origin and early evolution of life is an inseparable part of the discipline of astrobiology.<ref>{{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 }}</ref> That encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.<ref name="Goals2016">{{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 }}</ref><ref name="NYT-20151218-jc">{{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 }}</ref><ref>{{cite news |last=Cockell |first=Charles S. |title=How the search for aliens can help sustain life on Earth |date=4 October 2012 |url=https://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 }}</ref>

=== Other ===

Astronomy and astrophysics have developed interdisciplinary links with other major scientific fields. Archaeoastronomy is the study of ancient or traditional astronomies in their cultural context, using archaeological and anthropological evidence.<ref>{{cite journal |last=Aveni |first=Anthony F. |author-link=Anthony F. Aveni |date=1995 |title=Frombork 1992: Where Worlds and Disciplines Collide |journal=Archaeoastronomy: Supplement to the Journal for the History of Astronomy |volume=26 |issue=20 |pages=S74–S79 |bibcode=1995JHAS...26...74A |doi=10.1177/002182869502602007 |s2cid=220911940 }}</ref> Astrostatistics is the application of statistics to the analysis of large quantities of observational astrophysical data.<ref name="Hilbe 2017">{{cite book |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=978-1-118-44511-2 }}</ref> As "forensic astronomy", finally, methods from astronomy have been used to solve problems of art history<ref>{{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 }}</ref><ref>{{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 }}</ref> and occasionally of law.<ref>{{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}}</ref>

== Amateur ==

[[File:Telescope trailer 22.jpg |upright |thumb |Amateur astronomers can build their own equipment, and hold star parties and gatherings, such as Stellafane.]]

Astronomy is one of the sciences to which amateurs can contribute the most.<ref>{{cite journal |last=Mims III |first=Forrest M. |title=Amateur Science—Strong Tradition, Bright Future |journal=Science |date=1999 |volume=284 |issue=5411 |pages=55–56 |doi=10.1126/science.284.5411.55 |quote=Astronomy has traditionally been among the most fertile fields for serious amateurs [...] |bibcode=1999Sci...284...55M |s2cid=162370774 }}</ref> Collectively, amateur astronomers observe celestial objects and phenomena, sometimes with consumer-level equipment or equipment that they build themselves. Common targets include the Sun, the Moon, planets, stars, comets, meteor showers, and deep-sky objects such as star clusters, galaxies, and nebulae. Astronomy clubs throughout the world have programs to help their members set up and run observational programs such as to observe all the objects in the Messier (110 objects) or Herschel 400 catalogues.<ref>{{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}}</ref><ref>{{cite web |last=Lodriguss |first=Jerry |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}}</ref> Most amateurs work at visible wavelengths, but some have experimented with wavelengths outside the visible spectrum. The pioneer of amateur radio astronomy, Karl Jansky, discovered a radio source at the centre of the Milky Way.<ref name="Imbriale 1998">{{cite journal |last=Imbriale |first=William A. |title=Introduction to "Electrical Disturbances Apparently of Extraterrestrial Origin" |journal=Proceedings of the IEEE |date=July 1998 |volume=86 |issue=7 |pages=1507–1509 |doi=10.1109/JPROC.1998.681377 |bibcode=1998IEEEP..86.1507I }}</ref> Some amateur astronomers use homemade telescopes or radio telescopes originally built for astronomy research (''e.g.'' the One-Mile Telescope).<ref>{{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}}</ref><ref>{{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}}</ref>

Amateurs can make occultation measurements to refine the orbits of minor planets. They can discover comets, and perform regular observations of variable stars. Improvements in digital technology have allowed amateurs to make advances in astrophotography.<ref>{{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}}</ref><ref>{{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}}</ref><ref>{{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}}</ref>

== Unsolved problems ==

In the 21st century, there remain important unanswered questions in astronomy. Some are cosmic in scope: for example, what are the dark matter and dark energy that dominate the evolution and fate of the cosmos?<ref name="physics questions">{{cite web |url=http://www.pnl.gov/energyscience/01-02/11-questions/11questions.htm |title=11 Physics Questions for the New Century |publisher=Pacific Northwest National Laboratory |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}}</ref> What will be the ultimate fate of the universe?<ref>{{cite web |last=Hinshaw |first=Gary |date=15 December 2005 |url=http://map.gsfc.nasa.gov/m_uni/uni_101fate.html |title=What is the Ultimate Fate of the Universe? |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}}</ref> Why is the abundance of lithium in the cosmos four times lower than predicted by the standard Big Bang model?<ref>{{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}}</ref> Others pertain to more specific classes of phenomena. For example, is the Solar System normal or atypical?<ref>{{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 |doi-access=free |arxiv=astro-ph/0407476 |bibcode=2004MNRAS.354..763B |s2cid=119552423 }}</ref> What is the origin of the stellar mass spectrum, i.e. why do astronomers observe the same distribution of stellar masses—the initial mass function—regardless of initial conditions?<ref>{{cite journal |last=Kroupa |first=Pavel |title=The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems |journal=Science |date=2002 |volume=295 |issue=5552 |pages=82–91 |doi=10.1126/science.1067524 |pmid=11778039 |arxiv=astro-ph/0201098 |bibcode=2002Sci...295...82K |s2cid=14084249}}</ref> Likewise, questions remain about the formation of the first galaxies,<ref>{{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}}</ref> the origin of supermassive black holes,<ref>{{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}}</ref> the source of ultra-high-energy cosmic rays,<ref>{{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 }}</ref> and whether there is other life in the Universe, especially other intelligent life.<ref>{{cite web |url=http://www.astrobio.net/debate/236/complex-life-elsewhere-in-the-universe |archive-url=https://web.archive.org/web/20110628214416/http://www.astrobio.net/debate/236/complex-life-elsewhere-in-the-universe |archive-date=28 June 2011 |title=Rare Earth: Complex Life Elsewhere in the Universe? |work=Astrobiology Magazine |access-date=12 August 2006 |date=15 July 2002}}</ref><ref>{{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}}</ref>

==Notes== {{noteslist}}

==See also==

* {{Annotated link |Cosmogony}} * {{Annotated link |Outline of astronomy}} * {{Annotated link |Outline of space science}} * {{Annotated link |Space exploration}} * {{Annotated link |Local (astronomy)}}

=== Lists ===

* Glossary of astronomy * List of astronomers * List of astronomical instruments * List of astronomical observatories * List of astronomy acronyms * List of astronomical societies * List of software for astronomy research and education

==References== {{Reflist}}

==Sources==

* {{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 }} * {{cite book |last=Harpaz |first=Amos |title=Stellar Evolution |date=1994 |isbn=978-1-56881-012-6 |url=https://books.google.com/books?id=kd4VEZv8oo0C |publisher=A K Peters |ref=none}} * {{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. |ref=none}}

==External links== {{Commons}} {{Wikibooks}}  * [http://ned.ipac.caltech.edu/ NASA/IPAC Extragalactic Database (NED)] ([http://ned.ipac.caltech.edu/Library/Distances/ NED-Distances]) * [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 * https://viewspace.org/ veiwspace.org - interactives and videos about astronomy

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