Editing History of astronomy

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{{Lead too short|date=August 2023}}
{{More citations needed|date=April 2025}}[[File:Ioannis Bayeri Rhainani Vranometria 1661 (84132277) (cropped).jpg|thumb|upright=1.35|The [[Northern Hemisphere]] page from [[Johann Bayer]]'s 1661 edition of ''[[Uranometria]]'' - the first [[atlas]] to have [[star chart]]s covering the entire [[celestial sphere]]]]
[[File:Ioannis Bayeri Rhainani Vranometria 1661 (84132460) (cropped).jpg|thumb|upright=1.35|[[Southern Hemisphere]]]]
The '''history of astronomy''' focuses on the contributions civilizations have made to further their understanding of the [[universe]] beyond earth's atmosphere.<ref>https://www.amnh.org/explore/ology/astronomy/whatisastronomy#:~:text=Astronomy%20is%20the%20study%20of,faraway%20galaxies%20and%20tiny%20particles{{Dead link|date=October 2024 |bot=InternetArchiveBot |fix-attempted=yes }}.</ref>
[[Astronomy]] is one of the oldest [[natural sciences]], achieving a high level of success in the second half of the first millennium. Astronomy has origins in the [[religious]], [[mythological]], [[cosmological]], calendrical, and [[astrological]] beliefs and practices of prehistory. Early astronomical records date back to the [[Babylonians]] around 1000 BCE. There is also astronomical evidence of interest from early Chinese, Central American and North European cultures.<ref>{{cite web | url=https://pages.uoregon.edu/jschombe/ast121/lectures/lec02.html | title=History of Astronomy }}</ref>

Astronomy was used by early [[cultures]] for a variety of reasons. These include timekeeping, [[navigation]], spiritual and religious practices, and agricultural planning. Ancient astronomers used their observations to chart the skies in an effort to learn about the workings of the universe. During the [[Renaissance]] Period, revolutionary ideas emerged about astronomy. One such idea was contributed in 1593 by Polish astronomer [[Nicolaus Copernicus]], who developed a heliocentric model that depicted the planets orbiting the sun. This was the start of the [[Copernican Revolution]],<ref>{{cite web | url=https://www.asc-csa.gc.ca/eng/astronomy/basics/brief-history-astronomy.asp | title=A brief history of astronomy | date=12 March 2020 }}</ref> with the invention of the [[telescope]] in 1608 playing a key part. Later developments included the [[reflecting telescope]], [[astronomical photography]], [[astronomical spectroscopy]], [[radio telescopes]], [[cosmic ray astronomy]], [[infrared telescopes]], [[space telescopes]],[[ultraviolet astronomy]], [[X-ray astronomy]], [[gamma-ray astronomy]], [[space probes]],  [[neutrino astronomy]], and [[gravitational-wave astronomy]].

The success of astronomy, compared to other sciences, was achieved because of several reasons. Astronomy was the first science to have a mathematical foundation and have sophisticated procedures such as using [[armillary spheres]] and quadrants. This provided a solid base for collecting and verifying data.<ref>{{cite journal | url=https://academic.oup.com/astrogeo/article/51/3/3.25/224270#94074640 | doi=10.1111/j.1468-4004.2010.51325.x | title=The impact of astronomy | date=2010 | last1=Fabian | first1=Andy | journal=Astronomy & Geophysics | volume=51 | issue=3 | pages=3.25–3.30 | bibcode=2010A&G....51c..25F }}</ref><ref>{{cite web | url=https://www.britannica.com/science/astronomy/History-of-astronomy | title=Astronomy - Ancient, Celestial, Observations |publisher=Encyclopedia Britannica }}</ref>
Throughout the years, astronomy has broadened into multiple subfields such as [[astrophysics]], [[observational astronomy]], [[theoretical astronomy]], and [[astrobiology]].<ref>{{cite web | url=https://www.space.com/16014-astronomy.html#section-history-of-astronomy-the-beginnings | title=Astronomy: Everything you need to know | website=[[Space.com]] | date=28 October 2022 }}</ref>

==Early history==
[[File:Equinozio da Pizzo Vento,tramonto fondachelli fantina, sicilia.JPG|thumb|Sunset at the [[equinox]] from the prehistoric site of Pizzo Vento at [[Fondachelli-Fantina|Fondachelli Fantina]], [[Sicily]]]]

Early [[culture]]s identified celestial objects with [[mythology|god]]s and spirits.<ref>{{Citation | first=Edwin C. | last=Krupp | date=2003 | title=Echoes of the Ancient Skies: The Astronomy of Lost Civilizations | pages=62–72 | series=Astronomy Series | publisher=Courier Dover Publications | isbn=0-486-42882-6 | url=https://books.google.com/books?id=7rMAJ87WTF0C&pg=PA70}}</ref> They related these objects (and their movements) to phenomena such as [[rain]], [[drought]], [[season]]s, and [[tide]]s. It is generally believed that the first astronomers were [[priest]]s who understood [[Astronomical object|celestial objects]] and events to be manifestations of the [[divinity|divine]], hence the connection to what is now called [[astrology]]. A 32,500-year-old carved ivory [[mammoth]] tusk could contain the oldest known star chart (resembling the [[constellation]] [[Orion (constellation)|Orion]]).<ref>{{cite news
  | first=David | last=Whitehouse
  | date=January 21, 2003
  | title='Oldest star chart' found | publisher=[[BBC]]
  | url=http://news.bbc.co.uk/2/hi/science/nature/2679675.stm | access-date=2009-09-29}}</ref> It has also been suggested that drawings on the wall of the [[Lascaux]] caves in France dating from 33,000 to 10,000 years ago could be a graphical representation of the [[Pleiades]], the [[Summer Triangle]], and the [[Northern Crown]].<ref>{{cite news
  | first=Jack | last=Lucentini
  | title=Dr. Michael A. Rappenglueck sees maps of the night sky, and images of shamanistic ritual teeming with cosmological meaning
  | publisher=space.
  | url=http://www.space.com/scienceastronomy/planetearth/cave_paintings_000810.html
  | access-date=2009-09-29}}</ref><ref>{{cite web|url=http://news.bbc.co.uk/2/hi/science/nature/871930.stm|title=BBC News – SCI/TECH – Ice Age star map discovered|website=news.bbc.co.uk|access-date=13 April 2018}}</ref> Ancient structures with possibly [[Archaeoastronomy#Alignments|astronomical alignments]] (such as [[Stonehenge]]) probably fulfilled astronomical, [[religion|religious]], and [[social function]]s.

[[Calendar]]s of the world have often been set by observations of the Sun and Moon (marking the [[day]], [[month]], and [[year]]) and were important to [[agriculture|agricultural]] societies, in which the harvest depended on planting at the correct time of year. The nearly full moon was also the only lighting for night-time travel into city markets.<ref>{{Citation | last = Nilsson | first = Martin P. | author-link = Martin P. Nilsson | year = 1920 | title = Primitive Time-Reckoning. A Study in the Origins and Development of the Art of Counting Time among the Primitive and Early Culture Peoples | publisher = C. W. K. Gleerup | place = Lund | series = Skrifter utgivna av Humanistiska Vetenskapssamfundet i Lund | volume = 1 | oclc = 458893999}}</ref>

The [[Gregorian calendar|common modern calendar]] is based on the [[Roman calendar]]. Although originally a [[lunar calendar]], it broke the traditional link of the month to the phases of the Moon and divided the year into twelve almost-equal months, that mostly alternated between thirty and thirty-one days. [[Julius Caesar]] instigated [[calendar reform]] in 46&nbsp;[[BCE|BC]] and introduced what is now called the [[Julian calendar]], based upon the [[leap year|{{frac|365|1|4}} day year length]] originally proposed by the 4th&nbsp;century&nbsp;[[BCE|BC]] Greek astronomer [[Callippus]].

===Prehistoric Europe===
{{Main|Archaeoastronomy}}

Ancient astronomical artifacts have been found throughout [[Europe]]. The artifacts demonstrate that Neolithic and Bronze Age Europeans had a sophisticated knowledge of [[mathematics]] and astronomy.

Among the discoveries are:
* Paleolithic archaeologist [[Alexander Marshack]] put forward a theory in 1972 that bone sticks from locations like Africa and Europe from possibly as long ago as 35,000 BC could be marked in ways that tracked the Moon's phases,<ref>{{cite book|last = Marshak|first =  Alexander|date =1972|publisher = Littlehampton Book Services Ltd|title = The Roots of Civilization: the cognitive beginnings of man's first art, symbol, and notation|isbn = 978-0297994497}}</ref>{{page needed|date=January 2019}} an interpretation that has met with criticism.<ref>{{cite journal|last = Davidson|first =  Iain|date =1993|publisher = American Anthropologistd|title = The Roots of Civilization: The Cognitive Beginnings of Man's First Art, Symbol and Notation|journal=American Anthropologist|volume=95|number=4|pages=1027–1028|doi=10.1525/aa.1993.95.4.02a00350}}</ref>
* The [[Warren Field]] calendar in the Dee River valley of [[Scotland]]'s [[Aberdeenshire]] was first [[excavation (archaeology)|excavated]] in 2004 but was revealed in 2013 as a find of huge significance. It is to date the oldest known calendar, created around 8,000&nbsp;BC and predating all other calendars by some 5,000 years. The calendar takes the form of an early [[Mesolithic]] monument containing a series of 12 pits which appear to help the observer track lunar months by mimicking the phases of the Moon. It also aligns to sunrise at the winter solstice, thus coordinating the solar year with the lunar cycles. The monument had been maintained and periodically reshaped, perhaps up to hundreds of times, in response to shifting solar/lunar cycles, over the course of 6,000 years, until the calendar fell out of use around 4,000 years ago.<ref>{{cite news | url=http://www.birmingham.ac.uk/research/our/news/items/beginning-of-time.aspx | work=University of Birmingham | title=The Beginning of Time? | date=2013 | access-date=2014-10-01 | archive-date=2013-09-21 | archive-url=https://web.archive.org/web/20130921162036/http://www.birmingham.ac.uk/research/our/news/items/beginning-of-time.aspx | url-status=dead }}</ref><ref>{{cite news| url=https://www.bbc.com/news/uk-scotland-north-east-orkney-shetland-23286928 | work=BBC News | title='World's oldest calendar' discovered in Scottish field | date=2013}}</ref><ref>{{cite news| url=http://news.nationalgeographic.com/news/2013/07/130715-worlds-oldest-calendar-lunar-cycle-pits-mesolithic-scotland/ | archive-url=https://web.archive.org/web/20130718061637/http://news.nationalgeographic.com/news/2013/07/130715-worlds-oldest-calendar-lunar-cycle-pits-mesolithic-scotland | url-status=dead | archive-date=July 18, 2013 | work=Roff Smith, National Geographic | title=World's Oldest Calendar Discovered in U.K. | date=July 15, 2013}}</ref><ref>{{citation |last1=V. Gaffney |title=Time and a Place: A luni-solar 'time-reckoner' from 8th millennium BC Scotland |journal=Internet Archaeology |issue=34 |date=2013 |url=http://intarch.ac.uk/journal/issue34/gaffney_index.html |doi=10.11141/ia.34.1 |access-date=7 Oct 2014 |display-authors=etal|doi-access=free}}</ref>
* [[Goseck circle]] is located in [[Germany]] and belongs to the [[linear pottery culture]]. First discovered in 1991, its significance was only clear after results from archaeological digs became available in 2004. The site is one of hundreds of similar [[circular enclosure]]s built in a region encompassing [[Austria]], [[Germany]], and the [[Czech Republic]] during a 200-year period starting shortly after 5000&nbsp;BC.<ref>{{cite news |url=http://www.sonnenobservatorium-goseck.info/|title=Sonnenobservatorium Goseck}}</ref>
[[File:Nebra disc 1.jpg|thumb|The [[Nebra sky disk]], Germany, 1800–1600 BC]]

* The [[Nebra sky disk|Nebra sky disc]] is a [[Bronze Age]] bronze disc that was buried in Germany, not far from the Goseck circle, around 1600&nbsp;BC. It measures about {{Convert|30|cm|abbr=on}} diameter with a mass of {{Convert|2.2|kg|abbr=on}} and displays a blue-green patina (from oxidization) inlaid with gold symbols. Found by archeological thieves in 1999 and recovered in Switzerland in 2002, it was soon recognized as a spectacular discovery, among the most important of the 20th century.<ref>{{citation |title=The Nebra Sky Disc |publisher=Landesamt für Denkmalpflege und Archäologie Sachsen-Anhalt / Landesmuseum für Vorgeschichte |url=http://www.lda-lsa.de/en/nebra_sky_disc/ |access-date=15 October 2014 |archive-date=12 April 2014 |archive-url=https://web.archive.org/web/20140412185921/http://www.lda-lsa.de/en/nebra_sky_disc |url-status=dead }}</ref><ref>{{citation |title=Nebra Sky Disc |publisher=UNESCO Memory of the World Programme |url=https://www.unesco.org/en/memory-world/nebra-sky-disc |access-date=2025-04-22}}</ref> Investigations revealed that the object had been in use around 400 years before burial (2000 BC), but that its use had been forgotten by the time of burial. The inlaid gold depicted the full moon, a crescent moon about 4 or 5 days old, and the [[Pleiades]] star cluster in a specific arrangement, forming the earliest known depiction of celestial phenomena. Twelve lunar months pass in 354 days, requiring a calendar to insert a leap month every two or three years in order to keep synchronized with the solar year's seasons (making it [[Lunisolar calendar|lunisolar]]). The earliest known descriptions of this coordination were recorded by the Babylonians in the sixth or seventh centuries BC, over one thousand years later. Those descriptions verified ancient knowledge of the Nebra sky disc's celestial depiction as the precise arrangement needed to judge when to insert the [[Intercalation (timekeeping)|intercalary month]] into a lunisolar calendar, making it an astronomical clock for regulating such a calendar a thousand or more years before any other known method.<ref>{{citation |title=The Sky Disc of Nebra: Bronze Age Sky Disc Deciphered |publisher=Deutsche Welle |date=2002 |url=http://www.bibliotecapleyades.net/arqueologia/nebra_disk.htm |access-date=15 October 2014}}</ref>
* The [[Kokino]] site, discovered in 2001, sits atop an extinct [[volcanic cone]] at an elevation of {{convert|1013|m|ft}}, occupying about 0.5 hectares overlooking the surrounding countryside in [[North Macedonia]]. A [[Bronze Age Balkans|Bronze Age]] [[Observatory|astronomical observatory]] was constructed there around 1900&nbsp;BC and continuously served the nearby community that lived there until about 700&nbsp;BC. The central space was used to observe the rising of the Sun and full moon. Three markings locate sunrise at the summer and winter solstices and at the two equinoxes. Four more give the minimum and maximum declinations of the full moon: in summer, and in winter. Two measure the lengths of lunar months. Together, they reconcile solar and lunar cycles in marking the 235 [[lunation]]s that occur during 19 solar years, regulating a lunar calendar. On a platform separate from the central space, at lower elevation, four stone seats (thrones) were made in north–south alignment, together with a trench marker cut in the eastern wall. This marker allows the rising Sun's light to fall on only the second throne, at midsummer (about July 31). It was used for ritual ceremony linking the ruler to the local sun god, and also marked the end of the growing season and time for harvest.<ref>{{citation |title=Archaeo-astronomical Site Kokino |work=UNESCO World Heritage |date=2009 |url=https://whc.unesco.org/en/tentativelists/5413/ |access-date=27 October 2014}}</ref>
[[File:Berlin Gold hat calendar.jpg|alt=|thumb|Calendrical functions of the [[Berlin Gold Hat]] c.&nbsp;1000&nbsp;BC]]
* [[Golden hat]]s of Germany, [[France]] and [[Switzerland]] dating from 1400 to 800&nbsp;BC are associated with the Bronze Age [[Urnfield culture]]. The Golden hats are decorated with a spiral [[Motif (visual arts)|motif]] of the [[Sun]] and the [[Moon]]. They were probably a kind of [[calendar]] used to [[calibrate]] between the [[lunar calendar|lunar]] and [[solar calendar]]s.<ref>{{cite news| url=https://books.google.com/books?id=h0BIkXNZJZsC&pg=PA262 | work=T. Douglas Price, Oxford University Press | title=Europe Before Rome: A Site-by-Site Tour of the Stone, Bronze, and Iron Ages | page=262 | date=2013| isbn=978-0-19-991470-8 | last1=Douglas Price | first1=T.}}</ref><ref>{{cite news| url=https://books.google.com/books?id=GdlzA3yUlTUC&pg=PA14 | work=Geoff Stray, Bloomsbury Publishing USA | title=The Mayan and Other Ancient Calendars | page=14 | date=2007| isbn=9780802716347 | last1=Stray | first1=Geoff}}</ref> Modern [[scholarship]] has demonstrated that the ornamentation of the gold leaf cones of the [[Golden Hat of Schifferstadt|Schifferstadt type]], to which the [[Berlin Gold Hat]] example belongs, represent systematic sequences in terms of number and types of ornaments per band.  A detailed study of the Berlin example, which is the only fully preserved one, showed that the symbols probably represent a [[lunisolar]] calendar. The object would have permitted the determination of dates or periods in both [[lunar calendar|lunar]] and [[solar calendar]]s.<ref name="L2">Wilfried Menghin (Hrsg.): ''Acta Praehistorica et Archaeologica.'' Unze, Potsdam 32.2000, S. 31–108. {{ISSN|0341-1184}}</ref>

==Ancient times==
===Mesopotamia===
{{Main|Babylonian astronomy}}
{{Further|Babylonian astrology|Babylonian calendar}}

[[File:Babylonian tablet recording Halley's comet.jpg|thumb|upright|Babylonian tablet in the [[British Museum]] recording [[Halley's Comet]] in 164&nbsp;BC]]

The origins of astronomy can be found in [[Mesopotamia]], the "land between the rivers" [[Tigris]] and [[Euphrates]], where the ancient kingdoms of [[Sumer]], [[Assyria]], and [[Babylonia]] were located. A form of writing known as [[cuneiform]] emerged among the Sumerians around 3500–3000 BC. Our knowledge of Sumerian astronomy is indirect, via the earliest Babylonian star catalogues dating from about 1200&nbsp;BC. The fact that many star names appear in Sumerian suggests a continuity reaching into the Early Bronze Age. [[Astral theology]], which gave planetary gods an important role in [[Mesopotamian mythology]] and [[Mesopotamian religion|religion]], began with the [[Sumer]]ians. They also used a [[sexagesimal]] (base 60) place-value number system, which simplified the task of recording very large and very small numbers. The modern practice of dividing a circle into 360 [[degree (angle)|degrees]], or an hour into 60 minutes, began with the Sumerians. For more information, see the articles on [[Babylonian numerals]] and [[Babylonian mathematics|mathematics]].

Mesopotamia is worldwide the place of the earliest known astronomer and poet by name: [[Enheduanna]], [[Akkadian Empire|Akkadian]] high priestess to the [[lunar deity]] [[Sin (mythology)|Nanna/Sin]] and princess, daughter of [[Sargon the Great]] ({{circa|2334}} &ndash; {{circa|2279}} BCE). She had the Moon tracked in her chambers and wrote poems about her divine Moon.<ref name="c099">{{cite magazine | last=Winkler | first=Elizabeth | title=The Struggle to Unearth the World's First Author | magazine=The New Yorker | date=2022-11-19 | url=https://www.newyorker.com/books/page-turner/the-struggle-to-unearth-the-worlds-first-author | access-date=2025-02-10}}</ref>

Classical sources frequently use the [[wikt:Chaldean|term Chaldeans]] for the astronomers of Mesopotamia, who were originally [[Ancient Chaldeans|a people]], before being identified with priest-scribes specializing in [[astrology]] and other forms of [[divination]].

The first evidence of recognition that astronomical phenomena are periodic and of the application of mathematics to their prediction is Babylonian. Tablets dating back to the [[First Babylonian dynasty|Old Babylonian period]] document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of [[cuneiform]] tablets known as the ''[[Enūma Anu Enlil]]''. The oldest significant astronomical text that we possess is Tablet 63 of the ''Enūma Anu Enlil'', the [[Venus tablet of Ammisaduqa|Venus tablet]] of [[Ammi-saduqa]], which lists the first and last visible risings of Venus over a period of about 21 years and is the earliest evidence that the phenomena of a planet were recognized as periodic. The [[MUL.APIN]] contains catalogues of stars and constellations as well as schemes for predicting [[heliacal rising]]s and the settings of the planets, lengths of daylight measured by a [[water clock]], [[gnomon]], shadows, and [[Intercalation (timekeeping)|intercalations]]. The Babylonian GU text arranges stars in 'strings' that lie along declination circles and thus measure right-ascensions or time-intervals, and also employs the stars of the zenith, which are also separated by given right-ascensional differences.<ref>{{Harvtxt|Pingree|1998}}; {{Harvtxt|Rochberg|2004}}; {{Harvtxt|Evans|1998}}.</ref>

A significant increase in the quality and frequency of Babylonian observations appeared during the reign of [[Nabonassar]] (747–733 BC). The systematic records of ominous phenomena in [[Babylonian astronomical diaries]] that began at this time allowed for the discovery of a repeating 18-year cycle of [[lunar eclipse]]s, for example. The Greek astronomer [[Ptolemy]] later used Nabonassar's reign to fix the beginning of an era, since he felt that the earliest usable observations began at this time.

The last stages in the development of Babylonian astronomy took place during the time of the [[Seleucid Empire]] (323–60 BC). In the 3rd century BC, astronomers began to use "goal-year texts" to predict the motions of the planets. These texts compiled records of past observations to find repeating occurrences of ominous phenomena for each planet. About the same time, or shortly afterwards, astronomers created mathematical models that allowed them to predict these phenomena directly, without consulting records. A notable Babylonian astronomer from this time was [[Seleucus of Seleucia]], who was a supporter of the [[heliocentrism|heliocentric model]].

Babylonian astronomy was the basis for much of what was done in [[Greek astronomy|Greek and Hellenistic astronomy]], in classical [[Indian astronomy]], in Sassanian Iran, in Byzantium, in Syria, in [[Islamic astronomy]], in Central Asia, and in Western Europe.<ref name="dp1998">{{Harvtxt|Pingree|1998}}</ref>

===India===
{{Main|Indian astronomy}}
{{Further|History of science#Indian astronomy}}
{{See also|Hindu astrology}}Astronomy in the Indian subcontinent dates back to the period of [[Indus Valley Civilisation]] during 3rd millennium BC, when it was used to create calendars.<ref name="Bely">{{cite book|url=https://books.google.com/books?id=PbLPel3zRdEC&pg=PA197|title=A Question and Answer Guide to Astronomy|author1=Pierre-Yves Bely|author2=Carol Christian|author3=Jean-René Roy|publisher=Cambridge University Press|year=2010|isbn=978-0-521-18066-5|page=197}}</ref> As the Indus Valley civilization did not leave behind written documents, the oldest extant Indian astronomical text is the [[Vedanga Jyotisha]], dating from the [[Vedic period]].<ref name="Cosmic">{{cite book|chapter-url=https://books.google.com/books?id=PFTGKi8fjvoC&pg=FA25|title=Cosmic Perspectives|last=Subbarayappa|first=B. V.|date=14 September 1989|publisher=Cambridge University Press|isbn=978-0-521-34354-1|editor=Biswas, S. K.|pages=25–40|chapter=Indian astronomy: An historical perspective|editor2=Mallik, D. C. V.|editor3=[[C. V. Vishveshwara|Vishveshwara, C. V.]]}}</ref> The Vedanga Jyotisha is attributed to Lagadha and has an internal date of approximately 1350&nbsp;BC, and describes rules for tracking the motions of the Sun and the Moon for the purposes of ritual. It is available in two recensions, one belonging to the Rig Veda, and the other to the Yajur Veda. According to the Vedanga Jyotisha, in a ''yuga'' or "era", there are 5 solar years, 67 lunar sidereal cycles, 1,830 days, 1,835 sidereal days, and 62 synodic months. During the sixth century, astronomy was influenced by the Greek and Byzantine astronomical traditions.<ref name="Bely" /><ref>Neugebauer, O. (1952) Tamil Astronomy: A Study in the History of Astronomy in India. Osiris, 10:252–276.</ref><ref>{{Cite journal |last=Kak |first=Subhash |date=1995 |title=The Astronomy of the Age of Geometric Altars |journal=Quarterly Journal of the Royal Astronomical Society |volume=36 |pages=385–395|bibcode=1995QJRAS..36..385K}}</ref>

[[Aryabhata]] (476–550), in his magnum opus ''[[Aryabhatiya]]'' (499), propounded a computational system based on a planetary model in which the Earth was taken to be [[Earth's rotation|spinning on its axis]] and the periods of the planets were given with respect to the Sun. He accurately calculated many astronomical constants, such as the periods of the planets, times of the [[solar eclipse|solar]] and [[lunar eclipse|lunar]] [[eclipse]]s, and the instantaneous motion of the Moon.<ref name="Joseph">{{harvtxt|Joseph|2000}}.</ref><ref>Thurston, H, ''Early Astronomy.'' Springer, 1994, p. 178–188.</ref>{{Page needed|date=September 2010}} Early followers of Aryabhata's model included [[Varāhamihira]], [[Brahmagupta]], and [[Bhāskara II]].

Astronomy was advanced during the [[Shunga Empire]], and many [[star catalogue]]s were produced during this time. The Shunga period is known{{According to whom|date=May 2017}} as the "Golden age of astronomy in India".
It saw the development of calculations for the motions and places of various planets, their rising and setting, [[Astronomical conjunction|conjunctions]], and the calculation of eclipses.

By the sixth century, Indian astronomers believed that comets were celestial bodies that re-appeared periodically. This was the view expressed in the sixth century by the astronomers [[Varahamihira]] and Bhadrabahu. The tenth-century astronomer [[Bhattotpala]] listed the names and estimated periods of certain comets, but it is not known how these figures were calculated or how accurate they were.<ref>{{cite book|url=https://books.google.com/books?id=ILBuYcGASxcC&pg=PA293|title=Exploring Ancient Skies: A Survey of Ancient and Cultural Astronomy|last1=Kelley|first1=David H.|last2=Milone|first2=Eugene F.|date=2011|page=293|publisher=Springer |isbn=9781441976246}}</ref>

===Greece and Hellenistic world===
{{Main|Ancient Greek astronomy}}
[[File:Antikythera Fragment A (Front).webp|thumb|The [[Antikythera Mechanism]] was an [[analog computer]] dating from between 200 BC to 80&nbsp;BC designed to calculate the positions of astronomical objects.]]

The [[Ancient Greeks]] developed astronomy, which they treated as a branch of mathematics, to a highly sophisticated level. The first geometrical, three-dimensional models to explain the apparent motion of the planets were developed in the 4th century BC by [[Eudoxus of Cnidus]] and [[Callippus of Cyzicus]]. Their models were based on nested homocentric spheres centered upon the Earth. Their younger contemporary [[Heraclides Ponticus]] proposed that the Earth rotates around its axis.

A different approach to celestial phenomena was taken by natural philosophers such as [[Plato]] and [[Aristotle]]. They were less concerned with developing mathematical predictive models than with developing an explanation of the reasons for the motions of the Cosmos. In his ''Timaeus'', Plato described the universe as a spherical body divided into circles carrying the planets and governed according to harmonic intervals by a [[Anima mundi|world soul]].<ref>Plato, ''Timaeus,'' 33B-36D</ref> Aristotle, drawing on the mathematical model of Eudoxus, proposed that the universe was made of a complex system of concentric [[Celestial spheres|spheres]], whose circular motions combined to carry the planets around the Earth.<ref>Aristotle, ''Metaphysics,'' 1072a18-1074a32</ref> This basic cosmological model prevailed, in various forms, until the 16th century.

In the 3rd century BC [[Aristarchus of Samos]] was the first to suggest a [[heliocentric]] system, although only fragmentary descriptions of his idea survive.<ref>{{harvtxt|Pedersen|1993|pp=55–6}}.</ref> [[Eratosthenes]] estimated the [[circumference of the Earth]] with great accuracy (see also: [[history of geodesy]]).<ref>{{harvtxt|Pedersen|1993|pp=45–7}}.</ref>

Greek geometrical astronomy developed away from the model of concentric spheres to employ more complex models in which an [[deferent|eccentric]] circle would carry around a smaller circle, called an [[epicycle]] which in turn carried around a planet. The first such model is attributed to [[Apollonius of Perga]] and further developments in it were carried out in the 2nd century BC by [[Hipparchus|Hipparchus of Nicea]]. Hipparchus made a number of other contributions, including the first measurement of [[precession]] and the compilation of the first star catalog in which he proposed our modern system of [[apparent magnitude]]s.

The [[Antikythera mechanism]], an [[Ancient Greece|ancient Greek]] astronomical observational device for calculating the movements of the Sun and the Moon, possibly the planets, dates from about 150–100 BC, and was the first ancestor of an astronomical [[computer]]. It was discovered in an ancient shipwreck off the Greek island of [[Antikythera]], between [[Kythera]] and [[Crete]]. The device became famous for its use of a [[differential gear]], previously believed to have been invented in the 16th century, and the miniaturization and complexity of its parts, comparable to a clock made in the 18th century. The original mechanism is displayed in the Bronze collection of the [[National Archaeological Museum of Athens]], accompanied by a replica.

===Ptolemaic system===
{{main article|Ptolemaic system}}

Depending on the historian's viewpoint, the acme or corruption{{citation needed|date=August 2023}}{{dubious|date=August 2023}} of Classical physical astronomy is seen with [[Ptolemy]], a Greco-Roman astronomer from Alexandria of Egypt, who wrote the classic comprehensive presentation of geocentric astronomy, the ''Megale Syntaxis'' (Great Synthesis), better known by its Arabic title ''[[Almagest]]'', which had a lasting effect on astronomy up to the [[Renaissance]]. In his ''Planetary Hypotheses'', Ptolemy ventured into the realm of cosmology, developing a physical model of his geometric system, in a universe many times smaller than the more realistic conception of [[Aristarchus of Samos]] four centuries earlier.

===Egypt===
{{Main|Egyptian astronomy}}
[[File:Senenmut-Grab.JPG|thumb|Segment of the [[astronomical ceiling of Senenmut's Tomb]] (circa 1479–1458 BC), depicting constellations, protective deities, and twenty-four segmented wheels for the hours of the day and the months of the year]]

The precise orientation of the [[Egyptian pyramids]] affords a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BC. It has been shown the Pyramids were aligned towards the [[pole star]], which, because of the [[precession of the equinoxes]], was at that time [[Thuban]], a faint star in the constellation of [[Draco (constellation)|Draco]].<ref>Ruggles, C.L.N. (2005), ''Ancient Astronomy'', pages 354–355. ABC-Clio. {{ISBN|1-85109-477-6}}.</ref> Evaluation of the site of the temple of [[Amun-Re]] at [[Karnak]], taking into account the change over time of the [[obliquity of the ecliptic]], has shown that the Great Temple was aligned on the rising of the [[winter solstice|midwinter]] Sun.<ref>Krupp, E.C. (1988). "Light in the Temples", in C.L.N. Ruggles: Records in Stone: Papers in Memory of Alexander Thom. CUP, 473–499. {{ISBN|0-521-33381-4}}.</ref> The length of the corridor down which sunlight would travel would have limited illumination at other times of the year. The Egyptians also found the position of Sirius (the dog star), who they believed was Anubis, their jackal-headed god, moving through the heavens. Its position was critical to their civilisation as when it rose heliacal in the east before sunrise it foretold the flooding of the Nile. It is also the origin of the phrase "dog days of summer".<ref>{{Cite web |title=dog days {{!}} Etymology, origin and meaning of phrase dog days by etymonline |url=https://www.etymonline.com/word/dog%20days |access-date=2023-11-01 |website=www.etymonline.com}}</ref>

Astronomy played a considerable part in [[religious]] matters for fixing the dates of festivals and determining the hours of the [[night]]. The titles of several temple books are preserved recording the movements and phases of the [[Sun]], [[Moon]], and [[star]]s. The rising of [[Sirius]] ([[Egyptian language|Egyptian]]: Sopdet, [[Ancient Greek|Greek]]: Sothis) at the beginning of the inundation was a particularly important point to fix in the yearly calendar.

Writing in the [[Roman era]], [[Clement of Alexandria]] gives some idea of the importance of astronomical observations to the sacred rites:
<blockquote>And after the Singer advances the Astrologer (ὡροσκόπος), with a ''horologium'' (ὡρολόγιον) in his hand, and a ''palm'' (φοίνιξ), the symbols of [[ancient Egyptian astronomy|astrology]]. He must know by heart the [[Hermetism|Hermetic]] astrological books, which are four in number. Of these, one is about the arrangement of the fixed stars that are visible; one on the positions of the Sun and Moon and five planets; one on the conjunctions and phases of the Sun and Moon; and one concerns their risings.<ref>Clement of Alexandria, ''Stromata'', vi. 4</ref></blockquote>

The Astrologer's instruments (''horologium'' and ''palm'') are a [[plumb line]] and sighting instrument{{Clarify|date=November 2009}}<!--SEE TALK!-->. They have been identified with two inscribed objects in the [[Egyptian Museum of Berlin|Berlin Museum]]; a short handle from which a plumb line was hung, and a palm branch with a sight-slit in the broader end. The latter was held close to the eye, the former in the other hand, perhaps at arm's length. The "Hermetic" books which Clement refers to are the Egyptian theological texts, which probably have nothing to do with [[Hellenistic]] [[Hermetism]].<ref>Neugebauer O, ''Egyptian Planetary Texts'', Transactions, American Philosophical Society, Vol. 32, Part 2, 1942, Page 237.</ref>

From the tables of stars on the ceiling of the tombs of [[Rameses VI|Rameses&nbsp;VI]] and [[Rameses IX|Rameses&nbsp;IX]] it seems that for fixing the hours of the night a man seated on the ground faced the Astrologer in such a position that the line of observation of the [[pole star]] passed over the middle of his head. On the different days of the year each hour was determined by a fixed star [[culmination|culminating]] or nearly culminating in it, and the position of these stars at the time is given in the tables as in the centre, on the left eye, on the right shoulder, etc. According to the texts, in founding or rebuilding temples the [[north]] axis was determined by the same apparatus, and we may conclude that it was the usual one for astronomical observations. In careful hands it might give results of a high degree of accuracy.

===China===
{{Main|Chinese astronomy}}
{{See also|Book of Silk|Chinese astrology|Timeline of Chinese astronomy}}
[[Image:Su Song Star Map 2.JPG|thumb|[[History of typography in East Asia|Printed]] star map of [[Su Song]] (1020–1101) showing the south polar projection]]

The astronomy of [[East Asia]] began in [[China]]. [[Solar term]] was completed in [[Warring States period]]. The knowledge of Chinese astronomy was introduced into East Asia.

Astronomy in China has a long history. Detailed records of astronomical observations were kept from about the 6th century BC, until the introduction of Western astronomy and the telescope in the 17th century. Chinese astronomers were able to precisely predict eclipses.

Much of early Chinese astronomy was for the purpose of timekeeping. The Chinese used a lunisolar calendar, but because the cycles of the Sun and the Moon are different, astronomers often prepared new calendars and made observations for that purpose.

Astrological divination was also an important part of astronomy. Astronomers took careful note of [[Guest star (astronomy)|"guest stars"]] ({{Lang-zh|c=客星|p=kèxīng|l=guest star}}) which suddenly appeared among the [[fixed star]]s. They were the first to record a supernova, in the Astrological Annals of the Houhanshu in 185&nbsp;AD. Also, the supernova that created the [[Crab Nebula]] in 1054 is an example of a "guest star" observed by Chinese astronomers, although it was not recorded by their European contemporaries. Ancient astronomical records of phenomena like supernovae and comets are sometimes used in modern astronomical studies.

The world's first [[star catalogue]] was made by [[Gan De]], a [[:Category:Chinese astronomers|Chinese astronomer]], in the 4th century BC.

===Mesoamerica===
{{Main|Maya astronomy|Maya calendar|Aztec calendar}}
[[File:Chichen Itza Observatory 2 1.jpg|thumb|"El Caracol" observatory temple at [[Chichen Itza]], [[Mexico]]]]
[[Maya civilization|Maya]] astronomical [[Maya codices|codices]] include detailed tables for calculating [[Lunar phases|phases of the Moon]], the recurrence of eclipses, and the appearance and disappearance of [[Venus]] as morning and [[Venus#Observability|evening star]]. The Maya based their [[Maya calendar|calendrics]] in the carefully calculated cycles of the [[Pleiades]], the [[Sun]], the [[Moon]], [[Venus]], [[Jupiter]], [[Saturn]], [[Mars]], and also they had a precise description of the eclipses as depicted in the [[Dresden Codex]], as well as the ecliptic or zodiac, and the [[Milky Way]] was crucial in their Cosmology.<ref>[http://www.authenticmaya.com/maya_astronomy.htm Maya Astronomy] {{webarchive|url=https://web.archive.org/web/20070606210812/http://www.authenticmaya.com/maya_astronomy.htm|date=2007-06-06}}</ref> A number of important Maya structures are believed to have been oriented toward the extreme risings and settings of Venus. To the ancient Maya, Venus was the patron of war and many recorded battles are believed to have been timed to the motions of this planet. Mars is also mentioned in preserved astronomical codices and early [[Maya mythology|mythology]].<ref>{{harvtxt|Aveni|1980|pp=173–99}}.</ref>

Although the [[Maya calendar]] was not tied to the Sun, [[John E. Teeple|John Teeple]] has proposed that the Maya calculated the [[tropical year|solar year]] to somewhat greater accuracy than the [[Gregorian calendar]].<ref>{{harvtxt|Aveni|1980|pp=170–3}}.</ref> Both astronomy and an intricate numerological scheme for the measurement of time were vitally important components of [[Maya civilization#Religion|Maya religion]].

The Maya believed that the Earth was the center of all things, and that the stars, moons, and planets were gods. They believed that their movements were the gods traveling between the Earth and other celestial destinations. Many key events in Maya culture were timed around celestial events, in the belief that certain gods would be present.<ref>{{Cite web |title=How Does Ancient Mayan Astronomy Portray the Sun, Moon and Planets? |url=https://www.thoughtco.com/ancient-maya-astronomy-2136314 |access-date=2022-03-25 |website=ThoughtCo}}</ref>

==Middle Ages==
===Middle East===
{{Main|Astronomy in the medieval Islamic world}}
{{See also|Maragheh observatory|Ulugh Beg Observatory|Constantinople observatory of Taqi ad-Din}}
[[File:Astolabio di ahmad ibn muhammad al-naqqash, ottone inciso, saragozza, 1079-1080.JPG|thumb|Arabic [[astrolabe]] from 1079 to 1080&nbsp;AD]]

The Arabic and the Persian world under [[Islam]] had become highly cultured, and many important works of knowledge from [[Greek astronomy]], [[Indian astronomy]], and Persian astronomy were translated into Arabic, which were then used and stored in libraries throughout the area. An important contribution by Islamic astronomers was their emphasis on [[observational astronomy]].<ref>{{citation|title=The Astronomical Manuscripts of Naṣīr al-Dīn Ṭūsī|author=Ute Ballay|journal=[[Arabica (journal)|Arabica]]|volume=37|issue=3|date=November 1990|pages=389–392 [389]|publisher=[[Brill Publishers]]|jstor=4057148|doi=10.1163/157005890X00050}}</ref> This led to the emergence of the first astronomical [[Observatory|observatories]] in the [[Muslim world]] by the early 9th century.<ref name = "Micheau-992-3">{{citation|last=Micheau|first=Francoise|title=The Scientific Institutions in the Medieval Near East|pages=992–3}}, in Roshdi Rashed & Régis Morelon (1996), ''[[Encyclopedia of the History of Arabic Science]]'', pp. 985–1007, [[Routledge]], London and New York.</ref><ref>{{Citation |last=Nas |first=Peter J |title=Urban Symbolism |date=1993 |publisher=Brill Academic Publishers |isbn=90-04-09855-0 |pages=350}}</ref> [[Zij]] star catalogues were produced at these observatories.

In the ninth century, Persian astrologer [[Albumasar]] was thought to be one of the greatest astrologer at that time. His practical manuals for training astrologers profoundly influenced Muslim intellectual history and, through translations, that of western Europe and Byzantium In the 10th century,<ref>{{cite encyclopedia | last = Pingree | first = David | title = Abū Ma'shar al-Balkhī, Ja'far ibn Muḥammad | encyclopedia = [[Dictionary of Scientific Biography]] | volume = 1 | pages = 32–39 | publisher = [[Charles Scribner's Sons]] | location = New York | year = 1970 | isbn = 0-684-10114-9 | url = http://www.encyclopedia.com/doc/1G2-2830900030.html}}</ref> Albumasar's "Introduction" was one of the most important sources for the recovery of Aristotle for medieval European scholars.<ref>Richard Lemay, ''Abu Ma'shar and Latin Aristotelianism in the Twelfth Century, The Recovery of Aristotle's Natural Philosophy through Iranian Astrology'', 1962.</ref> [[Abd al-Rahman al-Sufi]] (Azophi) carried out observations on the [[star]]s and described their positions, [[apparent magnitude|magnitude]]s, brightness, and [[colour]] and drawings for each constellation in his ''[[Book of Fixed Stars]]''. He also gave the first descriptions and pictures of "A Little Cloud" now known as the [[Andromeda Galaxy]]. He mentions it as lying before the mouth of a Big Fish, an Arabic [[constellation]]. This "cloud" was apparently commonly known to the [[Isfahan (city)|Isfahan]] astronomers, very probably before 905&nbsp;AD.<ref name="NSOG">{{Citation |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= 0-943396-58-1 |pages=18}}</ref> The first recorded mention of the [[Large Magellanic Cloud]] was also given by al-Sufi.<ref name="obspm">{{cite web  | title=Observatoire de Paris (Abd-al-Rahman Al Sufi)  | url=http://messier.obspm.fr/xtra/Bios/alsufi.html  | access-date=2007-04-19}}</ref><ref name="obspm2">{{cite web  | publisher =Observatoire de Paris|title = The Large Magellanic Cloud, LMC  | url=http://messier.obspm.fr/xtra/ngc/lmc.html  |date = 11 March 2004}}</ref> In 1006, [[Ali ibn Ridwan]] observed [[SN 1006]], the brightest [[supernova]] in recorded history, and left a detailed description of the temporary star.

In the late tenth century, a huge observatory was built near [[Tehran]], [[Iran]], by the astronomer [[Abu-Mahmud al-Khujandi]] who observed a series of [[Meridian (astronomy)|meridian]] [[Astronomical transit|transits]] of the Sun, which allowed him to calculate the tilt of the Earth's axis relative to the Sun. He noted that measurements by earlier (Indian, then Greek) astronomers had found higher values for this angle, possible evidence that the axial tilt is not constant but was in fact decreasing.<ref>[http://www.encyclopedia.com/doc/1G2-2830902295.html Al-Khujandi, Abu Ma?mud ?amid Ibn Al-Khi?r], ''Complete Dictionary of Scientific Biography'', 2008.</ref><ref>{{MacTutor|id=Al-Khujandi|title=Abu Mahmud Hamid ibn al-Khidr Al-Khujandi}}</ref> In 11th-century Persia, [[Omar Khayyám]] compiled many tables and performed a reformation of the [[calendar]] that was more accurate than the [[Julian Calendar|Julian]] and came close to the [[Gregorian calendar|Gregorian]].

Other Muslim advances in astronomy included the collection and correction of previous astronomical data, resolving significant problems in the [[Geocentric model|Ptolemaic model]], the development of the universal latitude-independent [[astrolabe]] by [[Arzachel]],<ref>{{Citation |last=Krebs |first=Robert E. |title=Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Middle Ages and the Renaissance |date=2004 |publisher=Greenwood Press |isbn=0-313-32433-6 |pages=196}}</ref> the invention of numerous other astronomical instruments, [[Ja'far Muhammad ibn Mūsā ibn Shākir]]'s belief that the [[Astronomical object|heavenly bodies]] and [[celestial sphere]]s were subject to the same [[physical law]]s as [[Earth]],<ref>{{cite journal | last1 = Saliba | first1 = George | author-link = George Saliba | year = 1994 | title = Early Arabic Critique of Ptolemaic Cosmology: A Ninth-Century Text on the Motion of the Celestial Spheres | journal = Journal for the History of Astronomy | volume = 25 | issue = 2 | pages = 115–141 [116] | doi=10.1177/002182869402500205| bibcode = 1994JHA....25..115S| s2cid = 122647517}}</ref> and the introduction of empirical testing by [[Ibn al-Shatir]], who produced the first model of [[Moon|lunar]] motion which matched physical observations.<ref>{{cite journal | last1 = Faruqi | first1 = Y. M. | year = 2006 | title = Contributions of Islamic scholars to the scientific enterprise | journal = International Education Journal | volume = 7 | issue = 4| pages = 395–396}}</ref>

[[Natural philosophy]] (particularly [[Aristotelian physics]]) was separated from astronomy by [[Ibn al-Haytham]] (Alhazen) in the 11th century, by Ibn al-Shatir in the 14th century,<ref>Roshdi Rashed (2007). "The Celestial Kinematics of Ibn al-Haytham", ''Arabic Sciences and Philosophy'' '''17''', p. 7-55. [[Cambridge University Press]].</ref> and Qushji in the 15th century.<ref name=Ragep>F. Jamil Ragep (2001), "Tusi and Copernicus: The Earth's Motion in Context", ''Science in Context'' '''14''' (1–2), p. 145–163. [[Cambridge University Press]].</ref>

=== India ===
{{Main|Kerala school of astronomy and mathematics}}
[[File:Jantar Mantar at Jaipur.jpg|thumb|Historical [[Jantar Mantar (Jaipur)|Jantar Mantar]] observatory in [[Jaipur]], India]][[Bhāskara II]] (1114–1185) was the head of the astronomical observatory at Ujjain, continuing the mathematical tradition of Brahmagupta. He wrote the ''Siddhantasiromani'' which consists of two parts: ''Goladhyaya'' (sphere) and ''Grahaganita'' (mathematics of the planets). He also calculated the time taken for the Sun to orbit the Earth to nine decimal places. The Buddhist University of [[Nalanda]] at the time offered formal courses in astronomical studies.

Other important astronomers from India include [[Madhava of Sangamagrama]], [[Nilakantha Somayaji]] and [[Jyeshtadeva]], who were members of the [[Kerala school of astronomy and mathematics]] from the 14th century to the 16th century. Nilakantha Somayaji, in his ''Aryabhatiyabhasya'', a commentary on Aryabhata's ''Aryabhatiya'', developed his own computational system for a partially [[heliocentrism|heliocentric]] planetary model, in which Mercury, Venus, [[Mars]], [[Jupiter]] and [[Saturn]] orbit the [[Sun]], which in turn orbits the [[Earth]], similar to the [[Tychonic system]] later proposed by [[Tycho Brahe]] in the late 16th century. Nilakantha's system, however, was mathematically more efficient than the Tychonic system, due to correctly taking into account the equation of the centre and [[latitude|latitudinal]] motion of Mercury and Venus. Most astronomers of the [[Kerala school of astronomy and mathematics]] who followed him accepted his planetary model.<ref name="Joseph408">{{harvtxt|Joseph|2000|p=408}}.</ref><ref name=":6">{{cite journal |last1=Ramasubramanian |first1=K. |last2=Srinivas |first2=M. D. |last3=Sriram |first3=M. S. |year=1994 |title=Modification of the earlier Indian planetary theory by the Kerala astronomers (c. 1500 AD) and the implied heliocentric picture of planetary motion |journal=[[Current Science]] |volume=66 |pages=784–790}}</ref>

===Western Europe===
{{Further|Science in the Middle Ages}}
[[File:Aratea 93v.jpg|thumb|9th-century diagram of the positions of the [[Classical planet|seven planets]] on 18 March 816, from the [[Leiden Aratea]]]]

After the significant contributions of Greek scholars to the development of astronomy, it entered a relatively static era in Western Europe from the Roman era through the 12th century. This lack of progress has led some astronomers to assert that nothing happened in Western European astronomy during the Middle Ages.<ref>Henry Smith Williams, ''The Great Astronomers'' (New York: Simon and Schuster, 1930), pp. 99–102 describes "the record of astronomical progress" from the Council of Nicea (325 AD) to the time of Copernicus (1543 AD) on four blank pages.</ref>  Recent investigations, however, have revealed a more complex picture of the study and teaching of astronomy in the period from the 4th to the 16th centuries.<ref>{{Harvtxt|McCluskey|1998}}</ref>

[[Western Europe]] entered the Middle Ages with great difficulties that affected the continent's intellectual production. The advanced astronomical treatises of [[classical antiquity]] were written in [[Greek language|Greek]], and with the decline of knowledge of that language, only simplified summaries and practical texts were available for study. The most influential writers to pass on this ancient tradition in [[Latin]] were [[Macrobius]], [[Pliny the Elder|Pliny]], [[Martianus Capella]], and [[Calcidius]].<ref>Bruce S. Eastwood, ''Ordering the Heavens: Roman Astronomy and Cosmology in the Carolingian Renaissance'', (Leiden: Brill, 2007) {{ISBN|978-90-04-16186-3}}.</ref>  In the 6th century Bishop [[Gregory of Tours]] noted that he had learned his astronomy from reading Martianus Capella, and went on to employ this rudimentary astronomy to describe a method by which monks could determine the time of prayer at night by watching the stars.<ref>{{Harvtxt|McCluskey|1998|pp = 101–110}}</ref>

In the 7th century the English monk [[Bede of Jarrow]] published an influential text, ''[[De temporum ratione|On the Reckoning of Time]]'', providing churchmen with the practical astronomical knowledge needed to compute the proper date of [[Easter]] using a procedure called the ''[[computus]]''. This text remained an important element of the education of clergy from the 7th century until well after the rise of the [[Medieval university#Origins|Universities]] in the [[Renaissance of the 12th century|12th century]].<ref>Faith Wallis, ed. and trans, ''Bede: The Reckoning of Time'', (Liverpool: Liverpool University Press, 2004), pp. xviii–xxxiv {{ISBN|0-85323-693-3}}</ref>

The range of surviving ancient Roman writings on astronomy and the teachings of Bede and his followers began to be studied in earnest during the [[Carolingian Renaissance|revival of learning]] sponsored by the emperor [[Charlemagne]].<ref>{{Harvtxt|McCluskey|1998|pp = 131–164}}</ref>  By the 9th century rudimentary techniques for calculating the position of the planets were circulating in Western Europe; medieval scholars recognized their flaws, but texts describing these techniques continued to be copied, reflecting an interest in the motions of the planets and in their astrological significance.<ref>David Juste, "Neither Observation nor Astronomical Tables: An Alternative Way of Computing the Planetary Longitudes in the Early Western Middle Ages," pp. 181–222 in Charles Burnett, Jan P. Hogendijk, [[Kim Plofker]], and Michio Yano, ''Studies in the Exact Sciences in Honour of David Pingree'', (Leiden: Brill, 2004)</ref>

Building on this astronomical background, in the 10th century European scholars such as [[Gerbert of Aurillac]] began to travel to Spain and Sicily to seek out learning which they had heard existed in the Arabic-speaking world. There they first encountered various practical astronomical techniques concerning the calendar and timekeeping, most notably those dealing with the [[astrolabe]]. Soon scholars such as [[Hermann of Reichenau]] were writing texts in Latin on the uses and construction of the astrolabe and others, such as [[Walcher of Malvern]], were using the astrolabe to observe the time of eclipses in order to test the validity of computistical tables.<ref>{{Harvtxt|McCluskey|1998|pp = 171–187}}</ref>

By the 12th century, scholars were traveling to Spain and Sicily to seek out more advanced astronomical and astrological texts, which they [[Latin translations of the 12th century|translated into Latin]] from Arabic and Greek to further enrich the astronomical knowledge of Western Europe. The arrival of these new texts coincided with the rise of the universities in medieval Europe, in which they soon found a home.<ref>{{Harvtxt|McCluskey|1998|pp = 188–192}}</ref>  Reflecting the introduction of astronomy into the universities, [[Johannes de Sacrobosco|John of Sacrobosco]] wrote a series of influential introductory astronomy textbooks: the [[De sphaera mundi|Sphere]], a Computus, a text on the [[Quadrant (instrument)|Quadrant]], and another on Calculation.<ref>{{cite journal | last1 = Pedersen | first1 = Olaf | year = 1985 | title = In Quest of Sacrobosco | journal = Journal for the History of Astronomy | volume = 16 | issue = 3 | pages = 175–221 |bibcode = 1985JHA....16..175P | doi = 10.1177/002182868501600302 | s2cid = 118227787}}</ref>

In the 14th century, [[Nicole Oresme]], later bishop of Liseux, showed that neither the scriptural texts nor the physical arguments advanced against the movement of the Earth were demonstrative and adduced the argument of simplicity for the theory that the Earth moves, and ''not'' the heavens. However, he concluded "everyone maintains, and I think myself, that the heavens do move and not the earth: For God hath established the world which shall not be moved."<ref>Nicole Oresme, ''Le Livre du ciel et du monde'', xxv, ed. A. D. Menut and A. J. Denomy, trans. A. D. Menut, (Madison: Univ. of Wisconsin Pr., 1968), quotation at pp. 536–7.</ref> In the 15th century, Cardinal [[Nicholas of Cusa]] suggested in some of his scientific writings that the Earth revolved around the Sun, and that each star is itself a distant sun.

==Renaissance and Early Modern Europe==
{{anchor|Renaissance and Early Modern Europe}}

===Copernican Revolution===
{{See also|Astronomia nova|Epitome Astronomiae Copernicanae}}
During the renaissance period, astronomy began to undergo a revolution in thought known as the [[Copernican Revolution]], which gets the name from the astronomer [[Nicolaus Copernicus]], who proposed a heliocentric system, in which the planets revolved around the Sun and not the Earth. His ''[[De revolutionibus orbium coelestium]]'' was published in 1543.<ref name=":0">Westman, Robert S. (2011). ''The Copernican Question: Prognostication, Skepticism, and Celestial Order''. Los Angeles: University of California Press. {{ISBN|9780520254817}}.</ref> While in the long term this was a very controversial claim, in the very beginning it only brought minor controversy.<ref name=":0" /> The theory became the dominant view because many figures, most notably [[Galileo Galilei]], [[Johannes Kepler]] and [[Isaac Newton]] championed and improved upon the work. Other figures also aided this new model despite not believing the overall theory, like [[Tycho Brahe]], with his well-known observations.<ref name=":1">[[John Louis Emil Dreyer]], ''Tycho Brahe: a Picture of Scientific Life and Work in the Sixteenth Century'', A. & C. Black (1890), pp. 162–3</ref>

Brahe, a Danish noble, was an essential astronomer in this period.<ref name=":1" /> He came on the astronomical scene with the publication of ''De nova stella'', in which he disproved conventional wisdom on the supernova [[SN 1572]]<ref name=":1" /> (As bright as Venus at its peak, SN 1572 later became invisible to the naked eye, disproving  the [[Aristotle|Aristotelian]] doctrine of the immutability of the heavens.)<ref name=":11">{{cite journal|last=Kollerstrom|first=N.|author-link=Nicholas Kollerstrom|date=October 2004|title=Galileo and the new star|url=http://www.dioi.org/kn/NewStar.pdf|journal=[[Astronomy Now]]|volume=18|issue=10|pages=58–59|bibcode=2004AsNow..18j..58K|issn=0951-9726|access-date=20 February 2017}}</ref><ref name=ruiz>{{cite journal|arxiv=astro-ph/0309009|bibcode=2004ApJ...612..357R|title=Tycho Brahe's Supernova: Light from Centuries Past|journal=The Astrophysical Journal|volume=612|pages=357–363|last1=Ruiz-Lapuente|first1=Pilar|year=2004|issue=1|doi=10.1086/422419|s2cid=15830343}}</ref> He also created the [[Tychonic system]], where the Sun and Moon and the stars revolve around the Earth, but the other five planets revolve around the Sun. This system blended the mathematical benefits of the Copernican system with the "physical benefits" of the Ptolemaic system.<ref name="Westman, Robert S 1975 p. 322">[[Patronage in astronomy#Robert Westman|Westman, Robert S.]] (1975). ''The Copernican achievement''. University of California Press. p. 322. {{ISBN|978-0-520-02877-7}}. [[OCLC]] 164221945.</ref> This was one of the systems people believed in when they did not accept heliocentrism, but could no longer accept the Ptolemaic system.<ref name="Westman, Robert S 1975 p. 322"/> He is most known for his highly accurate observations of the stars and the planets. Later he moved to Prague and continued his work. In Prague he was at work on the [[Rudolphine Tables]], that were not finished until after his death.<ref name=":2">Athreya, A.; Gingerich, O. (December 1996). "An Analysis of Kepler's Rudolphine Tables and Implications for the Reception of His Physical Astronomy". ''Bulletin of the American Astronomical Society''. '''28''' (4): 1305.</ref> The Rudolphine Tables was a star map designed to be more accurate than either the [[Alfonsine tables]], made in the 1300s, and the [[Prutenic Tables]], which were inaccurate.<ref name=":2" /> He was assisted at this time by his assistant Johannes Kepler, who would later use his observations to finish Brahe's works and for his theories as well.<ref name=":2" />

After the death of Brahe, Kepler was deemed his successor and was given the job of completing Brahe's uncompleted works, like the Rudolphine Tables.<ref name=":2" /> He completed the Rudolphine Tables in 1624, although it was not published for several years.<ref name=":2" /> Like many other figures of this era, he was subject to religious and political troubles, like the [[Thirty Years' War]], which led to chaos that almost destroyed some of his works. Kepler was, however, the first to attempt to derive mathematical predictions of celestial motions from assumed physical causes. He discovered the three [[Kepler's laws of planetary motion]] that now carry his name, those laws being as follows:

# The orbit of a planet is an ellipse with the Sun at one of the two foci.
# A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
# The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.<ref>{{harvtxt|Stephenson|1994|p=170}}.</ref>

With these laws, he managed to improve upon the existing heliocentric model. The first two were published in 1609. Kepler's contributions improved upon the overall system, giving it more credibility because it adequately explained events and could cause more reliable predictions. Before this, the Copernican model was just as unreliable as the Ptolemaic model.  This improvement came because Kepler realized the orbits were not perfect circles, but ellipses.

===Galileo===
[[Image:galileo.arp.300pix.jpg|thumb|[[Galileo Galilei]] (1564–1642) crafted his own telescope and discovered that the Moon had craters, that Jupiter had moons, that the Sun had spots, and that Venus had phases like the Moon. Portrait by [[Justus Sustermans]].]] The invention of the [[telescope]] in 1608 revolutionized the study of astronomy. [[Galileo Galilei]] was among the first to use a telescope<ref>http://galileo.rice.edu/sci/instruments/telescope.html</ref> to observe the sky, after constructing a 20x refractor telescope.<ref>GINGERICH, O. (2011). Galileo, the Impact of the Telescope, and the Birth of Modern Astronomy. ''Proceedings of the American Philosophical Society,'' ''155'' (2), 134–141.</ref> He discovered the four largest moons of Jupiter in 1610, which are now collectively known as the [[Galilean moons]], in his honor.<ref name=":3">"Satellites of Jupiter". ''The Galileo Project''. [[Rice University]]. 1995.</ref> This discovery was the first known observation of satellites orbiting another planet.<ref name=":3" /> He also found that the Moon had craters and observed, and correctly explained sunspots, and that Venus exhibited a full set of phases resembling lunar phases.<ref name=":4">{{cite web|url=http://solar-center.stanford.edu/gal-challenge/gquiz6c.htm|title=How did Galileo prove the Earth was not the center of the solar system?|access-date=13 April 2021|publisher=Stanford Solar Center}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Galileo argued that these facts demonstrated incompatibility with the Ptolemaic model, which could not explain the phenomenon and would even contradict it.<ref name=":4" /> With Jupiter's moons, he demonstrated that the Earth does not have to have everything orbiting it and that other bodies could orbit another planet, such as the Earth orbiting the Sun.<ref name=":3" /> In the Ptolemaic system the celestial bodies were supposed to be perfect so such objects should not have craters or sunspots.<ref>Lawson, Russell M. (2004). ''Science in the Ancient World: An Encyclopedia''. [[ABC-CLIO]]. pp. 29–30. {{ISBN|1851095349}}.</ref> The phases of Venus could only happen in the event that Venus orbits around the Sun, which did not happen in the Ptolemaic system. He, as the most famous example, had to face challenges from church officials, more specifically the [[Roman Inquisition]].<ref name=":5">Finnocchiaro, Maurice (1989). ''The Galileo Affair''. Berkeley and Los Angeles, California: University of California Press. p. 291.</ref> They accused him of heresy because these beliefs went against the teachings of the Roman Catholic Church and were challenging the Catholic church's authority when it was at its weakest.<ref name=":5" /> While he was able to avoid punishment for a little while he was eventually tried and pled guilty to heresy in 1633.<ref name=":5" /> Although this came at some expense, his book was banned, and he was put under house arrest until he died in 1642.<ref>{{cite book|title=Parallax: The Race to Measure the Cosmos|last=Hirschfeld|first=Alan|date=2001|publisher=Henry Holt|isbn=978-0-8050-7133-7|location=New York, New York}}</ref>[[Image:Table of Astronomy, Cyclopaedia, Volume 1, p 164.jpg|thumb|left|Plate with figures illustrating articles on astronomy, from the 1728 ''[[Cyclopædia, or an Universal Dictionary of Arts and Sciences|Cyclopædia]]'']] [[Sir Isaac Newton]] developed further ties between physics and astronomy through his [[Newton's law of universal gravitation|law of universal gravitation]]. Realizing that the same force that attracts objects to the surface of the Earth held the Moon in orbit around the Earth, Newton was able to explain – in one theoretical framework – all known gravitational phenomena. In his ''[[Philosophiæ Naturalis Principia Mathematica]]'', he derived Kepler's laws from first principles. Those first principles are as follows:

# In an [[inertial frame of reference]], an object either remains at rest or continues to move at constant [[velocity]], unless acted upon by a [[force]].
# In an inertial reference frame, the [[vector sum]] of the forces F on an object is equal to the [[mass]] m of that object multiplied by the [[acceleration]] a of the object: F = ma. (It is assumed here that the mass m is constant)
# When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.<ref>Andrew Motte translation of Newton's ''Principia'' (1687) ''Axioms or Laws of Motion''</ref>

Thus while Kepler explained how the planets moved, Newton accurately managed to explain why the planets moved the way they do. Newton's theoretical developments laid many of the foundations of modern physics.

===Completing the Solar System===
Outside of England, Newton's theory took some time to become established. [[René Descartes]]' [[Descartes' vortex theory|theory of vortices]] held sway in France, and [[Christiaan Huygens]], [[Gottfried Wilhelm Leibniz]] and [[Jacques Cassini]] accepted only parts of Newton's system, preferring their own philosophies. [[Voltaire]] published a popular account in 1738.<ref>
{{cite book|first=Walter W.|last=Bryant|title=A History of Astronomy|date=1907|url=https://archive.org/stream/AHistoryOfAstronomy/Bryant-AHistoryOfAstronomy#page/n75|page=53}}
</ref> In 1748, the [[French Academy of Sciences]] offered a reward for solving the question of the perturbations of Jupiter and Saturn, which was eventually done by [[Euler]] and [[Lagrange]]. [[Laplace]] completed the theory of the planets, publishing from 1798 to 1825. The early origins of the [[nebular hypothesis|solar nebular model]] of planetary formation had begun.

[[Edmond Halley]] succeeded [[John Flamsteed]] as [[Astronomer Royal]] in England and succeeded in predicting the return of the [[Halley's comet|comet that bears his name]] in 1758. [[William Herschel]] found the first new planet, [[Uranus]], to be observed in modern times in 1781. The gap between the planets Mars and Jupiter disclosed by the [[Titius–Bode law]] was filled by the discovery of the [[asteroid]]s [[Ceres (dwarf planet)|Ceres]] and [[2 Pallas|Pallas]] in 1801 and 1802 with many more following.

At first, [[Colonial American Astronomy|astronomical thought in America]] was based on [[Aristotelian philosophy]],<ref>{{Citation|last=Brasch|first=Frederick|author-link=Frederick Edward Brasch|title=The Royal Society of London and its Influence upon Scientific Thought in the American Colonies|journal=The Scientific Monthly|date=October 1931|volume=33|issue=4|pages=338|postscript=.}}</ref> but interest in the new astronomy began to appear in [[Almanacs]] as early as 1659.<ref>{{Citation|last=Morison|first=Samuel Eliot|title=The Harvard School of Astronomy in the Seventeenth Century|journal=The New England Quarterly|date=March 1934|volume=7|issue=1|pages=3–24|postscript=.|doi=10.2307/359264|jstor=359264}}</ref>

===Stellar astronomy===
[[Cosmic pluralism]] is the name given to the idea that the stars are distant suns, perhaps with their own planetary systems.
Ideas in this direction were expressed in antiquity, by [[Anaxagoras]] and  by [[Aristarchus of Samos]], but did not find mainstream acceptance. The first astronomer of the European Renaissance to suggest that the stars were distant suns was [[Giordano Bruno]] in his ''De l'infinito universo et mondi'' (1584). This idea, together with a belief in intelligent extraterrestrial life, was among the charges brought against him by the Inquisition.
The idea became mainstream in the later 17th century, especially following the publication of ''[[Conversations on the Plurality of Worlds]]'' by [[Bernard Le Bovier de Fontenelle]] (1686), and by the early 18th century it was the default working assumptions in stellar astronomy.

The Italian astronomer [[Geminiano Montanari]] recorded observing variations in luminosity of the star [[Algol]] in 1667. Edmond Halley published the first measurements of the [[proper motion]] of a pair of nearby "fixed" stars, demonstrating that they had changed positions since the time of the ancient [[Ancient Greece|Greek]] astronomers Ptolemy and Hipparchus. [[William Herschel]] was the first astronomer to attempt to determine the distribution of stars in the sky. During the 1780s, he established a series of gauges in 600 directions and counted the stars observed along each line of sight. From this he deduced that the number of stars steadily increased toward one side of the sky, in the direction of the Milky Way [[Galactic Center|core]]. His son [[John Herschel]] repeated this study in the southern hemisphere and found a corresponding increase in the same direction.<ref>{{cite journal
 | last=Proctor | first=Richard A.
 | title=Are any of the nebulæ star-systems? | journal=Nature
 | date=1870 | pages=331–333
 | url=http://digicoll.library.wisc.edu/cgi-bin/HistSciTech/HistSciTech-idx?type=div&did=HISTSCITECH.0012.0052.0005&isize=M
 | issue=13
 | doi=10.1038/001331a0 | volume=1 |bibcode= 1870Natur...1..331P| doi-access=free}}</ref> In addition to his other accomplishments, William Herschel is noted for his discovery that some stars do not merely lie along the same line of sight, but are physical companions that form binary star systems.<ref name="Magill1992">{{cite book|author=Frank Northen Magill|title=Magill's Survey of Science: A-Cherenkov detectors|url=https://books.google.com/books?id=W33WAAAAMAAJ|year=1992|publisher=Salem Press|isbn=978-0-89356-619-7|page=219}}</ref>

==Modern astronomy==
{{further|Astronomy|Observational astronomy|Physical cosmology#History of study}}

===19th century===
[[Image:Karte Mars Schiaparelli MKL1888.png|thumb|[[Mars]] surface map of [[Giovanni Schiaparelli]]]]

Pre-photography, data recording of astronomical data was limited by the human eye. In 1840, [[John W. Draper]], a chemist, created the earliest known astronomical photograph of the Moon. And by the late 19th century thousands of photographic plates of images of planets, stars, and galaxies were created. Most photography had lower quantum efficiency (i.e. captured less of the incident photons) than human eyes but had the advantage of long integration times (100 ms for the human eye compared to hours for photos). This vastly increased the data available to astronomers, which led to the rise of [[human computers]], famously the [[Harvard Computers]], to track and analyze the data.

Scientists began discovering forms of light which were invisible to the naked eye: [[X-ray]]s, [[gamma ray]]s, [[radio wave]]s, [[microwave]]s, [[ultraviolet radiation]], and [[infrared radiation]]. This had a major impact on astronomy, spawning the fields of [[infrared astronomy]], [[radio astronomy]], [[x-ray astronomy]] and finally [[gamma-ray astronomy]]. With the advent of [[spectroscopy]] it was proven that other stars were similar to the Sun, but with a range of [[temperature]]s, [[mass]]es and sizes.

The science of [[astronomical spectroscopy|stellar spectroscopy]] was pioneered by [[Joseph von Fraunhofer]] and [[Angelo Secchi]]. By comparing the spectra of stars such as [[Sirius]] to the Sun, they found differences in the strength and number of their [[spectral line|absorption lines]]—the dark lines in stellar spectra caused by the atmosphere's absorption of specific frequencies. In 1865, Secchi began classifying stars into [[stellar classification|spectral types]].<ref>{{cite web
 | last=MacDonnell | first=Joseph
 | url=http://www.faculty.fairfield.edu/jmac/sj/scientists/secchi.htm
 | archive-url=https://web.archive.org/web/20110721210124/http://www.faculty.fairfield.edu/jmac/sj/scientists/secchi.htm
 | archive-date=2011-07-21
 | title=Angelo Secchi, S.J. (1818–1878) the Father of Astrophysics
 | publisher=[[Fairfield University]]
 | access-date=2006-10-02}}</ref> The first evidence of helium was observed on August 18, 1868, as a bright yellow spectral line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.

The first direct measurement of the distance to a star ([[61 Cygni]] at 11.4 [[light-years]]) was made in 1838 by [[Friedrich Bessel]] using the [[parallax]] technique. Parallax measurements demonstrated the vast separation of the stars in the heavens.{{Citation needed|date=October 2021}} Observation of double stars gained increasing importance during the 19th century. In 1834, Friedrich Bessel observed changes in the proper motion of the star Sirius and inferred a hidden companion. [[Edward Charles Pickering|Edward Pickering]] discovered the first [[spectroscopic binary]] in 1899 when he observed the periodic splitting of the spectral lines of the star [[Mizar (star)|Mizar]] in a 104-day period. Detailed observations of many binary star systems were collected by astronomers such as [[Friedrich Georg Wilhelm von Struve]] and [[Sherburne Wesley Burnham|S. W. Burnham]], allowing the masses of stars to be determined from the computation of [[orbital elements]]. The first solution to the problem of deriving an orbit of binary stars from telescope observations was made by Felix Savary in 1827.<ref>{{cite book
 | first=Robert G. | last=Aitken | title=The Binary Stars | page=66
 | publisher=Dover Publications Inc. | location=New York
 | date=1964 | isbn=978-0-486-61102-0}}</ref>
In 1847, [[Maria Mitchell]] discovered a comet using a telescope.

===20th century===
[[File:Hubble 01 Cropped.jpg|thumb|The [[Hubble Space Telescope]]]]

With the accumulation of large sets of astronomical data, teams like the [[Harvard Computers]] rose in prominence which led to many female astronomers, previously relegated as assistants to male astronomers, gaining recognition in the field. The [[United States Naval Observatory]] (USNO) and other astronomy research institutions hired [[Human computer|human "computers"]],  who performed the tedious calculations while scientists performed research requiring more background knowledge.<ref>{{Cite web|url=http://maia.usno.navy.mil/women_history/history.html|archive-url=https://web.archive.org/web/20041030073611/http://maia.usno.navy.mil/women_history/history.html|url-status=dead|archive-date=October 30, 2004|title=history of women|date=October 30, 2004}}</ref> A number of discoveries in this period were originally noted by the women "computers" and reported to their supervisors. [[Henrietta Swan Leavitt]] discovered the [[cepheid variable]] star [[period-luminosity relation]] which she further developed into a method of measuring distance outside of the Solar System.

A veteran of the Harvard Computers, [[Annie Jump Cannon|Annie J. Cannon]] developed the modern version of the stellar classification scheme in during the early 1900s (O B A F G K M, based on color and temperature), manually classifying more stars in a lifetime than anyone else (around 350,000).<ref name="HubenyMihalas2014">{{cite book|author1=Ivan Hubeny|author2=Dimitri Mihalas|title=Theory of Stellar Atmospheres: An Introduction to Astrophysical Non-equilibrium Quantitative Spectroscopic Analysis|url=https://books.google.com/books?id=TmuYDwAAQBAJ&pg=PA23|date=26 October 2014|publisher=Princeton University Press|isbn=978-0-691-16329-1|pages=23}}</ref><ref>{{Cite web|url=https://scriptamus.wordpress.com/2009/12/14/ladies-of-the-laboratory-2-how-in-a-few-months-late-in-the-19th-century-one-man-who-had-little-interest-in-gender-equality-hired-more-female-astronomers-than-the-world-had-ever-known/|title=Ladies of the Laboratory 2: How in a Few Months Late in the 19th Century One Man Who Had Little Interest in Gender Equality Hired More Female Astronomers than the World Had Ever Known|date=December 14, 2009}}</ref>
The twentieth century saw increasingly rapid advances in the scientific study of stars.
[[Karl Schwarzschild]] discovered that the color of a star and, hence, its temperature, could be determined by comparing the [[visual magnitude]] against the [[photographic magnitude]]. The development of the [[Photoelectric effect|photoelectric]] [[photometer]] allowed precise measurements of magnitude at multiple wavelength intervals. In 1921 [[Albert A. Michelson]] made the first measurements of a stellar diameter using an [[interferometer]] on the [[Mount Wilson Observatory#100-inch Hooker telescope|Hooker telescope]] at [[Mount Wilson Observatory]].<ref>{{cite journal
 | last1=Michelson | first1=A. A. | last2=Pease | first2=F. G.
 | title=Measurement of the diameter of Alpha Orionis with the interferometer
 | journal=Astrophysical Journal | date=1921 | volume=53 | issue=5 | pages=249–259
 | bibcode=1921ApJ....53..249M | doi= 10.1086/142603 | pmid=16586823 | s2cid=21969744 | pmc=1084808}}</ref>

[[File:PIA16874-CobeWmapPlanckComparison-20130321.jpg|thumb|left|Comparison of [[CMB]] (Cosmic microwave background) results from satellites [[Cosmic Background Explorer|COBE]], [[WMAP]] and ''[[Planck (spacecraft)|Planck]]'' documenting a progress in 1989–2013]]
Important theoretical work on the physical structure of stars occurred during the first decades of the twentieth century. In 1913, the [[Hertzsprung–Russell diagram]] was developed, propelling the astrophysical study of stars.
In [[Potsdam]] in 1906, the Danish astronomer [[Ejnar Hertzsprung]] published the first plots of color versus [[luminosity]] for these stars. These plots showed a prominent and continuous sequence of stars, which he named the Main Sequence.
At [[Princeton University]], [[Henry Norris Russell]] plotted the spectral types of these stars against their absolute magnitude, and found that dwarf stars followed a distinct relationship. This allowed the real brightness of a dwarf star to be predicted with reasonable accuracy.
Successful [[Stellar model|models]] were developed to explain the interiors of stars and stellar evolution. [[Cecilia Payne-Gaposchkin]] first proposed that stars were made primarily of hydrogen and helium in her 1925 doctoral thesis.<ref>{{cite web
 |url        = http://cwp.library.ucla.edu/Phase2/Payne-Gaposchkin,_Cecilia_Helena@861234567.html
 |archive-url = https://web.archive.org/web/20050318221903/http://cwp.library.ucla.edu/Phase2/Payne-Gaposchkin,_Cecilia_Helena@861234567.html
 |url-status=dead
 |archive-date = 2005-03-18
 |title      = " Payne-Gaposchkin, Cecilia Helena." CWP
 |publisher  = [[University of California]]
 |access-date = 2013-02-21
}}</ref> The spectra of stars were further understood through advances in [[quantum mechanics|quantum physics]]. This allowed the chemical composition of the stellar atmosphere to be determined.<ref name="new cosmos">{{cite book
 | last1=Unsöld | first1=Albrecht | title=The New Cosmos
 | publisher=Springer | location=New York
 | date=2001 | edition=5th | pages=180–185, 215–216
 | isbn=978-3-540-67877-9}}</ref>
As evolutionary models of stars were developed during the 1930s, [[Bengt Strömgren]] introduced the term Hertzsprung–Russell diagram to denote a luminosity-spectral class diagram.
A refined scheme for [[stellar classification]] was published in 1943 by [[William Wilson Morgan]] and [[Philip Childs Keenan]].

[[File:Milky way map.png|thumb|upright=1.4|Map of the [[Milky Way]] Galaxy, with the [[constellations]] that cross the [[galactic plane]] in each direction and the known prominent components annotated including [[Spiral arm|main arms]], spurs, bar, [[Galactic Center|nucleus/bulge]], notable [[nebulae]] and [[globular clusters]]]]
The existence of our [[galaxy]], the [[Milky Way]], as a separate group of stars was only proven in the 20th century, along with the existence of "external" galaxies, and soon after, the expansion of the [[universe]] seen in the recession of most galaxies from us. The "[[Great Debate (astronomy)|Great Debate]]" between [[Harlow Shapley]] and [[Heber Curtis]], in the 1920s, concerned the nature of the Milky Way, spiral nebulae, and the dimensions of the universe.<ref>{{cite web
 |last1=Weaver
 |first1=H. F.
 |title=Robert Julius Trumpler
 |url=http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
 |publisher=[[United States National Academy of Sciences|US National Academy of Sciences]]
 |access-date=January 5, 2007
 |archive-date=December 24, 2013
 |archive-url=https://web.archive.org/web/20131224112329/http://www.nap.edu/readingroom/books/biomems/rtrumpler.html
 |url-status=live
}}</ref>

With the advent of [[quantum physics]], [[spectroscopy]] was further refined.

The Sun was found to be part of a [[galaxy]] made up of more than 10<sup>10</sup> stars (10 billion stars). The existence of other galaxies, one of the matters of ''[[the great debate]]'', was settled by [[Edwin Hubble]], who identified the [[Andromeda Galaxy|Andromeda nebula]] as a different galaxy, and many others at large distances and receding, moving away from our galaxy.

[[Physical cosmology]], a discipline that has a large intersection with astronomy, made huge advances during the 20th century, with the model of the hot [[Big Bang]] heavily supported by the evidence provided by astronomy and physics, such as the [[redshift]]s of very distant galaxies and radio sources, the [[cosmic microwave background radiation]], [[Hubble's law]] and [[Big Bang nucleosynthesis|cosmological abundances of elements]].

==See also==
<!-- New links in alphabetical order please -->
{{div col|colwidth=30em}}
* [[Age of the universe]]
* [[Anthropic principle]]
* [[Astrotheology]]
* [[Expansion of the universe]]
* [[Hebrew astronomy]]
* [[History of astrology]]
* [[History of Mars observation]]
* [[History of supernova observation]]
* [[History of the telescope]]
* ''[[Letters on Sunspots]]''
* [[List of astronomers]]
** [[List of French astronomers]]
** [[List of Hungarian astronomers]]
** [[List of Russian astronomers and astrophysicists]]
** [[List of Slovenian astronomers]]
** [[List of women astronomers]]
* [[List of astronomical instrument makers]]
* [[List of astronomical observatories]]
* [[Patronage in astronomy]]
* [[Society for the History of Astronomy]]
* [[Timeline of astronomy]]
* [[Timeline of Solar System astronomy]]
* [[Worship of heavenly bodies]]
{{div col end}}

==References==
{{citation style|date=January 2024}}

===Citations===
{{Reflist}}

===Works cited===
* {{cite book |last=Aveni |first=Anthony F. |title=Skywatchers of Ancient Mexico |publisher=University of Texas Press |year=1980 |isbn=0-292-77557-1}}
* {{cite book |last=Evans |first=James |year=1998 |title=The History and Practice of Ancient Astronomy |publisher=Oxford University Press |isbn=0-19-509539-1}}
* {{cite book |first=George G. |last=Joseph |year=2000 |title=The Crest of the Peacock: Non-European Roots of Mathematics |edition=2nd |publisher=Penguin Books |place=London |isbn=0-691-00659-8}}
* {{cite book |last=McCluskey |first=Stephen C. |title=Astronomies and Cultures in Early Medieval Europe |publisher=Cambridge University Press |year=1998 |isbn=0-521-77852-2}}
* {{cite book |author-link=Olaf Pedersen |last=Pedersen |first=Olaf |year=1993 |title=Early Physics and Astronomy: A Historical Introduction |edition=rev. |publisher=Cambridge University Press |isbn=0-521-40899-7}}
* {{cite book |last=Pingree |first=David |author-link=David Pingree |date=1998 |contribution=Legacies in Astronomy and Celestial Omens |editor-last=Dalley |editor-first=Stephanie |editor-link=Stephanie Dalley |title=The Legacy of Mesopotamia |publisher=Oxford University Press |pages=125–137 |isbn =0-19-814946-8}}
* {{cite book |last=Rochberg |first=Francesca |year=2004 |title=The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture |publisher=Cambridge University Press}}{{missing ISBN}}
* {{cite book |last=Stephenson |first=Bruce |date=1994 |title=Kepler's Physical Astronomy |publisher=[[Princeton University Press]] |isbn=0-691-03652-7}}

==Further reading==
* {{cite book |last=Aaboe |first=Asger |author-link=Asger Aaboe |title=Episodes from the Early History of Astronomy |publisher=Springer-Verlag |year=2001 |isbn=0-387-95136-9 |ref=none}}
* {{cite book |last=Berry |first=Arthur |year=1898 |url=https://archive.org/details/shorthistoryofas025511mbp |title=A Brief History of Astronomy |via=[[Internet Archive]] |ref=none}}
* {{cite book |author-link=J. L. E. Dreyer |last=Dreyer |first=J. L. E. |title=History of Astronomy from Thales to Kepler |edition=2nd |publisher=Dover Publications |year=1953 |orig-year=1906 |ref=none}}
* {{cite book |last=Eastwood |first=Bruce |title=The Revival of Planetary Astronomy in Carolingian and Post-Carolingian Europe |series=Variorum Collected Studies Series |volume=CS 279 |publisher=Ashgate |year=2002 |isbn=0-86078-868-7 |ref=none}}
* {{cite book |editor-last=Hodson |editor-first=F. R. |title=The Place of Astronomy in the Ancient World: A Joint Symposium of the Royal Society and the British Academy |publisher=Oxford University Press |year=1974 |isbn=0-19-725944-8 |ref=none}}
* {{cite book |last=Hoskin |first=Michael |year=2003 |title=The History of Astronomy: A Very Short Introduction |publisher=Oxford University Press |isbn=0-19-280306-9 |ref=none}}
* {{cite arXiv |last=Magli |first=Giulio |title=On the possible discovery of precessional effects in ancient astronomy |eprint=physics/0407108 |year=2004 |ref=none}}
* {{cite book |edition=2 |publisher=[[Dover Publications]] |last=Neugebauer |first=Otto |author-link=Otto E. Neugebauer |title=The Exact Sciences in Antiquity |orig-year=1957 |year=1969 |isbn=978-0-486-22332-2 |ref=none}}
* {{cite book |author-link=Anton Pannekoek |last=Pannekoek |first=Anton |year=1989 |title=A History of Astronomy |publisher=Dover Publications |ref=none}}{{missing ISBN}}
* {{cite book |editor-last=Walker |editor-first=Christopher |title=Astronomy before the telescope |publisher=British Museum Press |year=1996 |isbn=0-7141-1746-3 |ref=none}}

==External links==
* {{commons category-inline}}
* [https://www.bbc.co.uk/programmes/p003c1cd Astronomy & Empire], BBC Radio 4 discussion with Simon Schaffer, Kristen Lippincott & Allan Chapman (''In Our Time'', May 4, 2006)
* [https://bibnum.obspm.fr/ Bibliothèque numérique de l'Observatoire de Paris] (Digital library of the Paris Observatory)
* [https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/home.html Caelum Antiquum]: Ancient Astronomy and Astrology Resources on [[LacusCurtius]]
* [https://jqjacobs.net/mesoamerica/meso_astro.html Mesoamerican Archaeoastronomy]:  A Review of Contemporary Understandings of Prehispanic Astronomical Knowledge
* [https://www.astronomicalheritage.net UNESCO-IAU Portal to the Heritage of Astronomy]

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