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{{short description|Swedish astronomer and physicist (1701–1744)}}
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{{Infobox scientist
| name              = Anders Celsius
| image             = Headshot of Anders Celsius.jpg
| image_size        = 215px
| caption           = Portrait by [[Olof Arenius]]
| birth_date        = {{birth date|df=yes|1701|11|27}}
| birth_place       = [[Uppsala]], [[Sweden]]
| death_date        = {{death date and age|df=yes|1744|04|25|1701|11|27}}
| death_place       = Uppsala, Sweden
| field             = [[Astronomy]], [[physics]], [[mathematics]], [[geology]]
| work_institutions = 
| alma_mater        = [[Uppsala University]]
| doctoral_advisor  = 
| doctoral_students = 
| known_for         = [[Celsius]]
| author_abbrev_bot = 
| prizes            = 
| signature         = Anders Celsius Signature.svg
| footnotes         = 
}}
'''Anders Celsius''' ({{IPA|sv|ˈânːdɛʂ ˈsɛ̌lːsɪɵs|lang}}; 27 November 1701{{snd}}25 April 1744)<ref name="EB1911" /> was a Swedish [[astronomer]], physicist and mathematician. He was professor of astronomy at [[Uppsala University]] from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the [[Uppsala Astronomical Observatory]] in 1741, and in 1742 proposed (an inverted form of) the centigrade [[temperature]] scale, which was later renamed [[Celsius]] in his honour.

==Early life and education==
Anders Celsius was born in [[Uppsala]], Sweden, on 27 November 1701.<ref name="EB1911" /> His family originated from [[Ovanåker]] in the province of [[Hälsingland]].<ref name="Bio">{{Cite web |title=Anders Celsius (1701-1744) |url=https://www.astro.uu.se/history/Celsius_eng.html |access-date=2022-04-23 |website=Uppasala Astronomical Observatory}}</ref> Their family estate was at ''Doma'', also known as ''Höjen'' or ''Högen'' (locally as ''Högen 2''). The name ''Celsius'' is a latinization of the estate's name (Latin {{Lang|la|celsus}} 'mound').

As the son of an astronomy professor, Nils Celsius, nephew of botanist [[Olof Celsius]] and the grandson of the mathematician [[Magnus Celsius]] and the astronomer [[Anders Spole]],<ref name=MacTutor>{{MacTutor|id=Celsius|title=Anders Celsius}}</ref>{{sfn | Collinder | 1970 | p=}}{{pn|date=April 2022}} Celsius chose a career in science. He was a talented mathematician from an early age. Anders Celsius studied at Uppsala University, where his father was a teacher, and in 1730 he, too, became a professor of astronomy there. Noted Swedish dramatic poet and actor Johan Celsius was also his uncle.<ref>{{Cite web |title=Johan Celsius - Svenskt Biografiskt Lexikon |url=https://sok.riksarkivet.se/sbl/Presentation.aspx?id=14759 |access-date=2022-08-23 |website=sok.riksarkivet.se}}</ref><ref>{{Cite web |title=My Heritage: Johan Celsius |url=https://www.myheritage.com/names/johan_celsius |access-date=2022-08-23 |website=www.myheritage.com}}</ref>

==Career==
In 1730, Celsius published the {{lang|la|Nova Methodus distantiam solis a terra determinandi}} (''New Method for Determining the Distance from the Earth to the Sun''). His research also involved the study of auroral phenomena, which he conducted with his assistant [[Olof Hiorter]], and he was the first to suggest a connection between the [[aurora borealis]] and changes in the magnetic field of the Earth. He observed the variations of a compass needle and found that larger deflections correlated with stronger auroral activity. At [[Nuremberg]] in 1733, he published a collection of 316 observations of the aurora borealis made by himself and others over the period 1716–1732.<ref name="EB1911">{{cite EB1911|wstitle=Celsius, Anders|volume=5|page=609}}</ref>

Celsius traveled frequently in the early 1730s, including to Germany, Italy and France, when he visited most of the major European observatories. In Paris he advocated the measurement of an [[arc of the meridian]] in [[Laponia (historical province)|Lapland]]. In 1736, he participated in the expedition organized for that purpose by the [[French Academy of Sciences]], led by the French mathematician [[Pierre Louis Maupertuis]] (1698–1759) to measure a degree of [[latitude]].<ref name="EB1911"/> The aim of the expedition was to measure the length of a degree along a meridian, close to the pole, and compare the result with a similar expedition to [[Peru]], today in [[Ecuador]], near the [[equator]]. The expeditions confirmed [[Isaac Newton]]'s belief that the shape of the Earth is an [[ellipsoid]] flattened at the poles.{{sfn | Collinder | 1970 | p=}}{{pn|date=April 2022}}

[[Image:AndersCelsiusyoung.jpg|thumb|left|200px|Anders Celsius c. 1730s]]
In 1738, he published the {{lang|la|De observationibus pro figura telluris determinanda}} (''Observations on Determining the Shape of the Earth''). Celsius's participation in the Lapland expedition won him much respect in Sweden with the government and his peers, and played a key role in generating interest from the Swedish authorities in donating the resources required to construct a new modern observatory in Uppsala.<ref name="Bio" /> He was successful in the request, and Celsius founded the [[Uppsala Astronomical Observatory]] in 1741.<ref>{{Cite web |title=History of Astronomy in Uppsala |url=https://www.astro.uu.se/history/ |access-date=2022-04-23 |website=Uppsala Astronomical Observatory}}</ref> The observatory was equipped with instruments purchased during his long voyage abroad, comprising the most modern instrumental technology of the period.<ref name="MacTutor" />

He made observations of eclipses and various astronomical objects and published catalogues of carefully determined magnitudes for some 300 stars using his own photometric system (mean error=0.4 mag).{{sfn | Collinder | 1970 | p=}}{{pn|date=April 2022}}{{sfn|Celsius|1742|pp=171–180|loc= [https://archive.org/stream/kungligasvenskav1317kung#page/232/mode/2up Fig. 1.]}}<ref name="history">{{Cite web|url=http://www.astro.uu.se/history/celsius_scale.html|title=History of the Celsius temperature scale|website=www.astro.uu.se}}</ref> In 1742 he proposed the Celsius temperature scale in a paper to the [[Royal Society of Sciences in Uppsala]], the oldest Swedish scientific society, founded in 1710. His thermometer was calibrated with a value of 0 for the boiling point of water and 100 for the freezing point. In 1745, a year after Celsius's death, the scale was reversed by [[Carl Linnaeus]] to facilitate more practical measurement.<ref name="reversed">{{Cite web|url=https://www.botan.uu.se/learning/linnaeus-online/the-life-of-Linnaeus/linnaeus-the-doctor-of-medicine/linnaeus-grows-bananas-and-comes-up-with-a-modern-thermometer/linnaeus-thermometer/|title=Linnaeus' thermometer |publisher=Uppsala University}}</ref>

[[Image:UppsalaCelsiusObservatory Busser.jpg|thumb|200px|right|The observatory of Anders Celsius, from a contemporary engraving]]
Celsius conducted many geographical measurements for the Swedish General map, and was one of earliest to note that much of Scandinavia is slowly rising above sea level, a continuous process which has been occurring since the melting of the ice from the latest [[Quaternary glaciation|ice age]]. However, he wrongly posed the notion that the water was [[evaporating]].{{sfn | Collinder | 1970 | p=}}{{pn|date=April 2022}}

In 1725 he became secretary of the Royal Society of Sciences in Uppsala, and served at this post until his death from [[tuberculosis]] in 1744. He supported the formation of the [[Royal Swedish Academy of Sciences]] in Stockholm in 1739 by Linnaeus and five others, and was elected a member at the first meeting of this academy. It was in fact Celsius who proposed the new academy's name.<ref>{{Cite web|url=https://runeberg.org/nfcl/0071.html|title=109-110 (Nordisk familjebok / Uggleupplagan. 32. Werth - Väderkvarn)|date=29 August 1921|website=runeberg.org}}</ref>

==Works==
[[File:Celsius, Anders – De novo in fluviis norlandiarum piscandi modo, 1738 – BEIC 8529648.jpg|thumb|''De novo in fluviis norlandiarum piscandi modo'', 1738]]
* {{Cite book|title=De novo in fluviis norlandiarum piscandi modo|volume=|publisher=Johan Höjer, änka|location=Uppsala|year=1738|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=8529648}}
*{{cite journal|last=Celsius|first= Anders |date=1742|url=https://archive.org/stream/kungligasvenskav1317kung#page/170/mode/2up/search |title=Observationer om twänne beständiga grader på en thermometer|trans-title=Observations about two stable degrees on a thermometer|lang=sv|journal=Kungliga Svenska Vetenskapsakademiens Handlingar (Proceedings of the Royal Swedish Academy of Sciences)|volume=3|pages= 171–180|display-authors=0 }}

== See also ==
* [[Celsius family]]
* [[Daniel Gabriel Fahrenheit]]

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

===Sources===
{{refbegin}}
* {{cite book | last=Collinder | first=P. | title=Swedish astronomers, 1477-1900 | publisher=Almqvist & Wiksells | series=Acta Universitatis Upsaliensis: Skrifter Rörande Uppsala Universitet | year=1970 | url=https://books.google.com/books?id=UcNMwgEACAAJ }}
{{refend}}

==External links==
{{Commons category}}
*[https://www.myheritage.com/names/johan_celsius  Johan Celsius - Historical records and family trees at MyHeritage]
[[Image:Gamla uppsala kyrka.jpg|thumb|right|300px|Celsius is buried at Uppsala Church in Gamla Uppsala next to his grandfather]]

{{Scientists whose names are used as SI units}}
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{{DEFAULTSORT:Celsius, Anders}}
[[Category:1701 births]]
[[Category:1744 deaths]]
[[Category:18th-century Swedish astronomers]]
[[Category:18th-century deaths from tuberculosis]]
[[Category:Scientists from Uppsala]]
[[Category:Uppsala University alumni]]
[[Category:Academic staff of Uppsala University]]
[[Category:Members of the Royal Swedish Academy of Sciences]]
[[Category:Tuberculosis deaths in Sweden]]
[[Category:18th-century Swedish mathematicians]]
[[Category:Fellows of the Royal Society]]
[[Category:Creators of temperature scales]]
[[Category:Age of Liberty people]]
[[Category:18th-century Swedish inventors]]