Aristarchus of Samos

{{Short description|Greek astronomer and mathematician (c. 310 – 230 BC)}}

{{Infobox person

| name = Aristarchus of Samos

| image = Aristarchos von Samos (Denkmal).jpeg

| caption = Statue of Aristarchus of Samos at the Aristotle University of Thessaloniki

| birth_date = {{circa}} 310 BC

| birth_place = Samos

| death_date = c. 230 BC

| death_place = Alexandria,{{cite web|url=http://www.worldhistory.biz/ancient-history/71176-aristarchus-of-samos.html|title=Aristarchus of Samos: Mathematician and astronomer|date= 8 September 2015|work=World History|archive-url=https://web.archive.org/web/20180507154131/http://www.worldhistory.biz/ancient-history/71176-aristarchus-of-samos.html|archive-date=7 May 2018|access-date=29 November 2018}} Ptolemaic Kingdom

| nationality = Greek

| occupation = {{hlist |Scholar |Mathematician |Astronomer}}

}}

Aristarchus of Samos ({{IPAc-en|ˌ|æ|r|ə|ˈ|s|t|ɑr|k|ə|s}}; {{langx|grc|Ἀρίσταρχος ὁ Σάμιος}}, {{tlit|grc|Aristarkhos ho Samios}}; {{circa|310|230 BC}}) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day. He also supported the theory of Anaxagoras according to which the Sun was just another star.[https://solar-center.stanford.edu/FAQ/Qsunasstar.html]

He likely moved to Alexandria, and he was a student of Strato of Lampsacus, who later became the third head of the Peripatetic school in Greece. According to Ptolemy, he observed the summer solstice of 280 BC.{{Cite journal|last=Huxley|first=George|date=30 May 1964|title=Aristarchus of Samos and Graeco-Babylonian Astronomy|url=https://grbs.library.duke.edu/article/view/11941|journal=Greek, Roman, and Byzantine Studies|volume=5|issue=2|pages=123–131|issn=2159-3159}} Along with his contributions to the heliocentric model, as reported by Vitruvius, he created two separate sundials: one that is a flat disc; and one hemispherical.{{Cite web|last=Sidoli|first=Nathan Camillo|date=22 December 2015|title=Aristarchus (1), of Samos, Greek astronomer, mathematician, 3rd century BC|url=https://oxfordre.com/classics/view/10.1093/acrefore/9780199381135.001.0001/acrefore-9780199381135-e-737|access-date=December 7, 2021|website=Oxford Classical Dictionary|language=en|doi=10.1093/acrefore/9780199381135.013.737|isbn=978-0-19-938113-5}}

Aristarchus estimated the sizes of the Sun and Moon as compared to Earth's size. He also estimated the distances from the Earth to the Sun and Moon. He estimated that the Sun is seven times the size of Earth. Although this estimate is inaccurate by an order of magnitude, his insight that the Sun is larger than the Earth convinced him that the Sun must be the center of the universe.

Aristarchus was influenced by the concept presented by Philolaus of Croton (c. 470 – 385 BC) of a fire at the center of the universe (i.e. by contemporary understanding, at the center of the Earth). Aristarchus recast this "central fire" as the Sun, and he arranged the other planets in their correct order of distance around the Sun.{{cite book|author-link=John William Draper|author=Draper, John William|chapter=History of the Conflict Between Religion and Science|editor=Joshi, S. T.|date=2007|orig-year=1874|title=The Agnostic Reader|pages=172–173|publisher=Prometheus|isbn=978-1-59102-533-7}}

Like Anaxagoras before him, Aristarchus suspected that the stars were just other bodies like the Sun, albeit farther away from Earth. His astronomical ideas were often rejected in favor of the geocentric theories of Aristotle and Ptolemy. Nicolaus Copernicus knew that Aristarchus had a 'moving Earth' theory, although it is unlikely that Copernicus was aware that it was a heliocentric theory.{{refn|name=AristarchusNote01a|The Greek mathematician and astronomer Aristarchus of Samos proposed such a system during the third century BC (Dreyer 1953, [https://archive.org/stream/historyofplaneta00dreyuoft#page/134/mode/2up pp. 135–48]). In an early unpublished manuscript of De Revolutionibus (which still survives in the Jagiellonian Library in Kraków), Copernicus wrote that "It is credible that... Philolaus believed in the mobility of the Earth and some even say that Aristarchus was of that opinion", a passage that was removed from the published edition, a decision described by Owen Gingerich as "eminently sensible" "from an editorial viewpoint". Philolaus was not a heliocentrist, as he thought that both the Earth and the Sun moved around a central fire. Gingerich says that there is no evidence that Copernicus was aware of the few clear references to Aristarchus's heliocentrism in ancient texts (as distinct from one other unclear and confusing one), especially Archimedes's The Sand-Reckoner (which was not in print until the year after Copernicus died), and that it would have been in his interest to mention them had he known of them, before concluding that he developed his idea and its justification independently of Aristarchus.Owen Gingerich, [http://adsabs.harvard.edu/full/1985JHA....16...37G#:~:text=There%20is%20no%20question%20but,were%20found%20independently%20by%20Copernicus. "Did Copernicus Owe a Debt to Aristarchus?"], Journal for the History of Astronomy, vol. 16, no. 1 (February 1985), pp. 37–42. "There is no question but that Aristarchus had the priority of the heliocentric idea. Yet there is no evidence that Copernicus owed him anything.(!9) As far as we can tell both the idea and its justification were found independently by Copernicus."}}For a (less recent) contrary view that Copernicus did know about Aristarchus's heliocentric theory see: {{cite book|author=George Kish|title=A Source Book in Geography|url=https://books.google.com/books?id=_6qF4vjZvhYC&pg=PA51|year=1978|publisher=Harvard University Press|isbn=978-0-674-82270-2|pages=51–52|quote=Copernicus himself admitted that the theory was attributed to Aristarchus, though this does not seem to be generally known... Here, however, there is no question of the Earth revolving around the sun, and there is no mention of Aristarchus. But it is a curious fact that Copernicus did mention the theory of Aristarchus in a passage which he later suppressed: }} The Philolaus-Aristarchus passage is then given in untranslated Latin, without further comment. This is then followed by quoting in full Archimedes's passage about Aristarchus's heliocentric theory from 'The Sand Reckoner' (using its alternative title Arenarius)', seemingly without mentioning that The Sand Reckoner was not in print until a year after Copernicus's death (unless this is mentioned in a passage not shown by Google Books.).

Aristarchus is considered one of the greatest astronomers of antiquity along with Hipparchus.

Heliocentrism

The original text has been lost, but a reference in a book by Archimedes, entitled The Sand Reckoner (Archimedis Syracusani Arenarius & Dimensio Circuli), describes a work in which Aristarchus advanced the heliocentric model as an alternative hypothesis to geocentrism:

{{blockquote|You are now aware ['you' being King Gelon] that the "universe" is the name given by most astronomers to the sphere the centre of which is the centre of the earth, while its radius is equal to the straight line between the centre of the sun and the centre of the earth. This is the common account (τὰ γραφόμενα) as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the "universe" just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same centre as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the centre of the sphere bears to its surface.Heath, Thomas (1913), [https://archive.org/stream/aristarchusofsam00heatuoft#page/302/mode/2up p. 302]. The italics and parenthetical comments are as they appear in Thomas Little Heath's original. From Arenarius, 4–5. In [http://www.heinrichfleck.net/Quaderni/Arenario-Greco.pdf the original]: "κατέχεις δέ, διότι καλείται κόσμος ὑπὸ μὲν τῶν πλείστων ἀστρολόγων ἁ σφαῖρα, ἇς ἐστι κέντρον μὲν τὸ τᾶς γᾶς κέντρον, ἁ δὲ ἐκ τοῦ κέντρου ἴσα τᾷ εὐθείᾳ τᾷ μεταξὺ τοῦ κέντρου τοῦ ἁλίου καὶ τοῦ κέντρου τᾶς γᾶς. ταῦτα γάρ ἐντι τὰ γραφόμενα, ὡς παρὰ τῶν ἀστρολόγων διάκουσας. ̓Αρίσταρχος δὲ ό Σάμιος ὑποθεσίων τινων ἐξέδωκεν γραφάς, ἐν αἷς ἐκ τῶν ὑποκειμένων συμβαίνει τὸν κόσμον πολλαπλάσιον εἶμεν τοῦ νῦν εἰρημένου. ὑποτιθέται γὰρ τὰ μὲν ἀπλανέα τῶν ἄστρων καὶ τὸν ἅλιον μένειν ἀκίνητον, τὰν δὲ γᾶν περιφερέσθαι περὶ τὸν ἅλιον κατὰ κύκλου περιφέρειαν, ὅς ἐστιν ἐν μέσῳ τῷ δρόμῳ κείμενος, τὰν δὲ τῶν ἀπλανέων ἄστρων σφαῖραν περὶ τὸ αὐτὸ κἐντρον²⁵ τῷ ἁλίῳ κειμέναν τῷ μεγέθει ταλικαύταν εἶμεν, ὥστε τὸν κύκλον, καθ’ ὃν τὰν γᾶν ὑποτιθέται περιφερέσθαι, τοιαύταν ἔχειν ἀναλογίαν ποτὶ τὰν τῶν ἀπλανέων ἀποστασίαν, οἵαν ἔχει τὸ κέντρον τᾶς σφαίρας ποτὶ τὰν επιφάνειαν." Heath mentions a proposal of Theodor Bergk that the word "δρόμῳ" ("orbit") may originally have been "ὀυρανῷ" ("heaven", thus correcting a grammatical incongruity) so that instead of "[the sun] lying in the middle of the orbit" we would have "[the circle] lying in the middle of the heaven".}}

Aristarchus knew that a moving-earth model would imply that the stars should exhibit parallax (that is, a movement of the stars relative to each other as the Earth moves around the Sun). However, since stellar parallax is only detectable with telescopes, it was not observed at the time. Aristarchus reconciled this issue by postulating that the stars were other suns that are very far away,{{cite web |website=solar-center.stanford.edu |url=http://solar-center.stanford.edu/FAQ/Qsunasstar.html |access-date=13 July 2014 |author=Louis Strous |title=Who discovered that the Sun was a star?}} far enough that the parallax was not observable. This implied a universe much larger than had been believed.

It is a common misconception that the heliocentric view was considered sacrilegious by the contemporaries of Aristarchus. Lucio Russo traces this to Gilles Ménage's printing of a passage from Plutarch's On the Apparent Face in the Orb of the Moon, in which Aristarchus jokes with Cleanthes, who is head of the Stoics, a sun worshipper, and opposed to heliocentrism.{{cite book|last1=Russo|first1=Lucio|author-link=Lucio Russo |translator-last=Levy|translator-first=Silvio |title=The Forgotten Revolution: How Science Was Born in 300 BC and Why it Had to Be Reborn|url=https://books.google.com/books?id=ld8lBAAAQBAJ&pg=PA82|access-date=13 June 2017|date=2013|publisher=Springer Science & Business Media|isbn=978-3642189043|page=82, fn.106}}; {{cite journal|last1=Russo|first1=Lucio |first2=Silvio M. |last2=Medaglia |year=1996 |title=Sulla presunta accusa di empietà ad Aristarco di Samo |jstor=20547344|journal=Quaderni Urbinati di Cultura Classica|publisher=Fabrizio Serra Editore|volume=New Series, Vol. 53|issue=2|pages=113–121|doi=10.2307/20547344 |language=it}} In the manuscript of Plutarch's text, Aristarchus says Cleanthes should be charged with impiety. Ménage's version, published shortly after the trials of Galileo and Giordano Bruno, transposes an accusative and nominative so that it is Aristarchus who is purported to be impious. The resulting misconception of an isolated and persecuted Aristarchus is still promulgated.{{cite web|url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:2008.01.0357:section=6&highlight=cleanthes|title=De facie quae in orbe lunae apparet, Section 6|last=Plutarch|work=Perseus Digital Library|publisher=Tufts University|access-date=13 June 2017}}

According to Plutarch, while Aristarchus postulated heliocentrism only as a hypothesis, Seleucus of Seleucia, a Hellenistic astronomer who lived a century after Aristarchus, maintained it as a definite opinion and gave a demonstration of it,Plutarch, Platonicae quaestiones, VIII, i but no full record of the demonstration has been found. In his Naturalis Historia, Pliny the Elder later wondered whether errors in the predictions about the heavens could be attributed to a displacement of the Earth from its central position.{{cite book|last=Neugebauer|first=O.|author-link=Otto E. Neugebauer|title=A History of Ancient Mathematical Astronomy|year=1975|pages=[https://books.google.com/books?id=6tkqBAAAQBAJ&pg=PA69 697–698]|publisher=Springer-Verlag|series=Studies in the History of Mathematics and Physical Sciences|volume=1}} PlinyNaturalis historia, II, 70 and SenecaNaturales quaestiones, VII, xxv, 6–7 referred to the retrograde motion of some planets as an apparent (unreal) phenomenon, which is an implication of heliocentrism rather than geocentrism. Still, no stellar parallax was observed, and Plato, Aristotle, and Ptolemy preferred the geocentric model that was believed throughout the Middle Ages.

The heliocentric theory was revived by Copernicus,{{cite book|author=Joseph A. Angelo|title=Encyclopedia of Space and Astronomy|url=https://books.google.com/books?id=VUWno1sOwnUC&pg=PA153|year=2014|publisher=Infobase Publishing|isbn=978-1-4381-1018-9|page=153}} after which Johannes Kepler described planetary motions with greater accuracy with his three laws. Isaac Newton later gave a theoretical explanation based on laws of gravitational attraction and dynamics.

After realizing that the Sun was much larger than the Earth and the other planets, Aristarchus concluded that planets revolved around the Sun.

Distance to the Sun

File:Aristarchus working.jpg

The only known work attributed to Aristarchus, On the Sizes and Distances of the Sun and Moon, is based on a geocentric worldview. Historically, it has been read as stating that the angle subtended by the Sun's diameter is two degrees, but Archimedes states in The Sand Reckoner that Aristarchus had a value of half a degree, which is much closer to the average value of 32' or 0.53 degrees. The discrepancy may come from a misinterpretation of which unit of measure was meant by a Greek term in the text of Aristarchus.{{cite journal|journal=Dio: The International Journal of Scientific History|url=http://www.dioi.org/vols/we0.pdf|title=Aristarchos Unbound: Ancient Vision The Hellenistic Heliocentrists' Colossal Universe-Scale Historians' Colossal Inversion of Great & Phony Ancients History-of-Astronomy and the Moon in Retrograde!|page=19|year=2008|volume=14|last=Rawlins|first=D.}}

Aristarchus claimed that at half moon (first or last quarter moon), the angle between the Sun and Moon was 87°.Greek Mathematical Works, Loeb Classical Library, Harvard University, 1939–1941, edited by Ivor Thomas, volume 2 (1941), pp. 6–7 Using correct geometry, but the insufficiently accurate 87° datum, Aristarchus concluded that the Sun was between 18 and 20 times farther away from the Earth than the Moon.[https://www.youtube.com/watch?v=LXHxx8L9YFo A video on reconstruction of Aristarchus' method], in Turkish without subtitles. (The correct value of this angle is close to 89° 50', and the Sun's distance is approximately 400 times that of the Moon.) The implicit inaccurate solar parallax of slightly under three degrees was used by astronomers up to and including Tycho Brahe, c. AD 1600. Aristarchus pointed out that the Moon and Sun have nearly equal apparent angular sizes, and therefore their diameters must be in proportion to their distances from Earth.{{cite book |author=Kragh, Helge |title=Conceptions of cosmos: from myths to the accelerating universe: a history of cosmology |publisher=Oxford University Press |date=2007 |page=26 |isbn=978-0-19-920916-3}}

Size of the Moon and Sun

In On the Sizes and Distances of the Sun and Moon, Aristarchus discusses the size of the Moon and Sun in relation to the Earth. In order to achieve these measurements and subsequent calculations, he used several key notes made while observing a lunar eclipse.{{Cite journal|last=Hirshfeld|first=Alan W.|date=2004|title=The Triangles of Aristarchus|url=https://www.jstor.org/stable/20871578|journal=The Mathematics Teacher|volume=97|issue=4|pages=228–231|doi=10.5951/MT.97.4.0228|jstor=20871578|issn=0025-5769}} The first of these consisted of the time that it took for the Earth's shadow to fully encompass the Moon, along with how long the Moon remained within the shadow. This was used to estimate the angular radius of the shadow.{{Cite journal|last=Batten|first=Alan H.|date=1981|title=Aristarchos of Samos|url=https://adsabs.harvard.edu/full/1981JRASC..75...29B|journal=Journal of the Royal Astronomical Society of Canada|volume=75|pages=29–35|bibcode=1981JRASC..75...29B}} From there, using the width of the cone that was created by the shadow in relation to the Moon, he determined that it was twice the diameter of the Moon at the full, non-central eclipse. In addition to this, Aristarchus estimated that the length of the shadow extended around 2.4 times the distance of the Moon from the Earth.File:Aristarchus and Herodotus craters Apollo 15.jpg (right), from Apollo 15, NASA photograph]]

Using these calculations, along with his estimated distances of the Sun from the Earth and Moon from the Earth, he created a triangle. Employing geometry similar to that he had already used for the distances, he was able to determine that the diameter of the Moon is roughly one-third of the Earth's diameter. In order to estimate the size of the Sun, Aristarchus considered the proportion of the Sun's distance to Earth in comparison to the Moon's distance from Earth, which was found to be roughly 18 to 20 times the length. Therefore, the size of the Sun is around 19 times wider than the Moon, making it approximately six times wider than the Earth's diameter.

Legacy

The lunar crater Aristarchus, the minor planet 3999 Aristarchus, and the telescope Aristarchos are named after him.

References

Bibliography

{{cite book |last=Heath |first=Sir Thomas |author-link=T.L. Heath |title=Aristarchus of Samos, the ancient Copernicus; a history of Greek astronomy to Aristarchus, together with Aristarchus's Treatise on the sizes and distances of the sun and moon : a new Greek text with translation and notes |url=https://archive.org/details/aristarchusofsam00heatuoft |date=1913 |publisher=Oxford University Press |location=London |ref=Reference-Heath-1913}}
{{cite book | title= A History of Astronomy from Thales to Kepler

| last= Dreyer

| first= John Louis Emil

| author-link= J. L. E. Dreyer

| year= 1953

| orig-year= 1906

| publisher=Dover Publications

| url=https://archive.org/details/historyofplaneta00dreyuoft

| location= New York

| ref=Reference-Dreyer-1953}}

External links

[http://adsabs.harvard.edu//full/seri/JRASC/0075//0000029.000.html Biography: JRASC, 75 (1981) 29]
[http://www.phy6.org/stargaze/Shipprc2.htm First estimate of the Moon's distance] and [http://www.phy6.org/stargaze/Sarist.htm First estimate of the Sun's distance] from educational website [http://www.phy6.org/stargaze/Sintro.htm From Stargazers to Starships]
Aristarchus of Samos, The Ancient Copernicus (https://archive.org/details/aristarchusofsam00heatuoft
{{MacTutor Biography|id=Aristarchus}}
[http://hos.ou.edu/galleries/01Ancient/Aristarchos/ Online Galleries, History of Science Collections, University of Oklahoma Libraries] {{Webarchive|url=https://web.archive.org/web/20120515203135/http://hos.ou.edu/galleries/01Ancient/Aristarchos/ |date=2012-05-15 }} High resolution images of works by Aristarchus of Samos in .jpg and .tiff format.

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Category:310s BC births

Category:230s BC deaths

Category:3rd-century BC Greek writers

Category:Ancient Greek astronomers

Category:Ancient Samians

Category:3rd-century BC Greek mathematicians