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Eratosthenes

Eratosthenes of Cyrene (/ɛrəˈtɒsθənz/; Greek: Ἐρατοσθένης [eratostʰénɛːs]; c. 276 BC – c. 195/194 BC) was a Greek polymath: a mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. His work is comparable to what is now known as the study of geography, and he introduced some of the terminology still used today.[1]

This article is about the Greek scholar of the third century BC. For other uses, see Eratosthenes (disambiguation).

Eratosthenes

276 BC[note 1]

Cyrene (in modern Libya)

194 BC (around age 82)[note 2]

  • Scholar
  • Librarian
  • Poet
  • Inventor

He is best known for being the first person known to calculate the circumference of the Earth, which he did by using the extensive survey results he could access in his role at the Library. His calculation was remarkably accurate.[2][3] He was also the first to calculate Earth's axial tilt, which has also proved to have remarkable accuracy.[4] He created the first global projection of the world, incorporating parallels and meridians based on the available geographic knowledge of his era.


Eratosthenes was the founder of scientific chronology;[5] he used Egyptian and Persian records to estimate the dates of the main events of the Trojan War, dating the sack of Troy to 1183 BC. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers and composite numbers.


He was a figure of influence in many fields who yearned to understand the complexities of the entire world.[6] His devotees nicknamed him Pentathlos after the Olympians who were well rounded competitors, for he had proven himself to be knowledgeable in every area of learning. Yet, according to an entry[7] in the Suda (a 10th-century encyclopedia), some critics scorned him, calling him Number 2 because he always came in second in all his endeavours.[8]

The first book was something of an introduction and gave a review of his predecessors, recognizing their contributions that he compiled in the library. In this book Eratosthenes denounced as not providing any insight into what he now described as geography. His disapproval of Homer's topography angered many who believed the world depicted in the Odyssey to be legitimate.[6][21] He also commented on the ideas of the nature and origin of the Earth: he thought of Earth as an immovable globe while its surface was changing. He hypothesized that at one time the Mediterranean had been a vast lake that covered the countries that surrounded it and that it only became connected to the ocean to the west when a passage opened up sometime in its history.

Homer

The second book contains his calculation of the circumference of the Earth. This is where, according to Pliny, "The world was grasped." Here Eratosthenes described his famous story of the well in Syene, wherein at noon each summer solstice, the Sun's rays shone straight down into the city-center well. This book would now be considered a text on mathematical geography.

[22]

His third book of the Geography contained . He cited countries and used parallel lines to divide the map into sections, to give accurate descriptions of the realms. This was a breakthrough and can be considered the beginning of geography. For this, Eratosthenes was named the "Father of Modern Geography."[17]

political geography

Platonikos (lost, quoted by )

Theon of Smyrna

Hermes

Erigone

Chronographies

Olympic Victors

Περὶ τῆς ἀναμετρήσεως τῆς γῆς (On the Measurement of the Earth) (lost, summarized by Cleomedes)

[30]

Гεωγραϕικά (Geographika) (lost, criticized by Strabo)

[25]

Arsinoe (a memoir of queen ; lost; quoted by Athenaeus in the Deipnosophistae)

Arsinoe

Ariston (concerning ' addiction to luxury; lost; quoted by Athenaeus in the Deipnosophistae)[31]

Aristo of Chios

The (Katasterismoi), a lost collection of Hellenistic myths about the constellations

Catasterismi

(c. 310 – c. 230 BC), a Greek mathematician who calculated the distance from the Earth to the Sun.

Aristarchus of Samos

on the Moon.

Eratosthenes (crater)

period in the lunar geologic timescale.

Eratosthenian

in the eastern Mediterranean Sea.

Eratosthenes Seamount

in Antarctica.

Eratosthenes Point

(c. 190 – c. 120 BC), a Greek mathematician who measured the radii of the Sun and the Moon as well as their distances from the Earth.

Hipparchus

(c. 135 – c. 51 BC), a Greek astronomer and mathematician who calculated the circumference of the Earth.

Posidonius

at Roger Pearse.

English translation of the primary source for Eratosthenes and the size of the Earth

Berlin, 1822 (PDF) (Latin/Greek), Reprinted Osnabruck 1968 (German)

Bernhardy, Gottfried: Eratosthenica

Archived 2001-03-01 at the Wayback Machine

Eratosthenes' sieve in Javascript

About Eratosthenes' methods, including a Java applet

How the Greeks estimated the distances to the Moon and Sun

Measuring the Earth with Eratosthenes' method

List of ancient Greek mathematicians and contemporaries of Eratosthenes

New Advent Encyclopedia article on the Library of Alexandria

Eratosthenes' sieve in classic BASIC all-web based interactive programming environment

Archived 2019-04-14 at the Wayback Machine : project fr:La main à la pâte.

International pedagogical project

Archived 2020-01-05 at the Wayback Machine

Open source Physics Computer Model about Eratosthenes estimation of radius and circumference of Earth

Eratosthenes, video

Eratosthenes, Katasterismoi (or Astrothesiae), original text