Cleomedes (Greek: Κλεομήδης) was a Greekastronomer who is known chiefly for his book On the Circular Motions of the Celestial Bodies (Κυκλικὴ θεωρία μετεώρων), also known as The Heavens (Latin: Caelestia).
His birth and death dates are not known—historians have suggested that he wrote his work sometime between the mid-1st century BC and 400 AD. The earlier estimates rely on the fact that Cleomedes refers extensively in his writing to the work of mathematician and astronomer Posidonius of Rhodes (c. 135 – c. 51 BC), and yet seemingly not at all to the work of Ptolemy (c. 100 – c. 170 AD). (Cleomedes also refers to Aristotle (384–322 BC), Pytheas of Massalia (310–306 BC), Aratus (c. 315/310 BC – 240 BC), Eratosthenes (276–195 BC), and Hipparchus (c. 190 – c. 120 BC). These conclusions have been challenged on the grounds that Cleomedes' work was in relatively elementary astronomy, and that reference to Ptolemy would not necessarily be expected. The 20th century mathematician Otto Neugebauer, however, looked closely at the astronomical observations made by Cleomedes, and concluded that a date of 371 AD (±50 years) better explains what is found there. Neugebauer's estimate has been challenged on the grounds that Cleomedes makes observational errors with enough frequency that there is difficulty in deciding which observations to trust for the purpose of dating his work.
On the Circular Motions of the Celestial Bodiesedit
The book for which Cleomedes is known is a fairly basic astronomy textbook in two volumes. His purpose in writing seems to have been as philosophical as it was scientific—he spends an extensive amount of time criticizing the scientific ideas of the Epicureans.
Cleomedes' book is valued primarily for preserving, apparently verbatim, much of Posidonius' writings on astronomy (none of Posidonius' books have survived to the modern day). Cleomedes is accurate in some of his remarks on lunar eclipses, especially his conjecture that the shadow on the Moon suggests a sphericalEarth. He also remarks presciently that the absolute size of many stars may exceed that of the Sun (and that the Earth might appear as a very small star, if viewed from the surface of the Sun).
This book is the original source for the well-known story of how Eratosthenes measured the Earth's circumference. Many modern mathematicians and astronomers believe the description to be reasonable (and believe Eratosthenes' achievement to be one of the more impressive accomplishments of ancient astronomy).
Cleomedes deserves credit for the earliest clear statement of the apparent distance explanation of the Sun Illusion or Moon Illusion. He argued that the sun appeared farther away on the horizon than in the zenith, and therefore larger (since its angular size was constant). He attributed this explanation to Posidonius.
Opticsedit
As a disciple of Posidonius, Cleomedes noted some elementary qualitative properties of refraction, such as the bending of a ray toward the perpendicular in passing from a less dense to a more dense medium, and suggested that due to atmospheric refraction, the Sun and its rainbow may be visible when the Sun is below the horizon.[1]
Legacyedit
Cleomedes is now memorialized by the crater Cleomedes in the northeastern portion of the visible Moon.
Alan C. Bowen, Robert B. Todd, Cleomedes' Lectures on Astronomy. A Translation of The Heavens with an Introduction and Commentary. University of California Press, 2004. ISBN0520233255
Helen E. Ross, "Cleomedes (c. 1st century AD) on the celestial illusion, atmospheric enlargement, and size-distance invariance". Perception, 2000, 29, 863–871.
External linksedit
On the Circular Motions of the Celestial Bodies, original text online and biography
English translation of the section on Eratosthenes and the size of the earth at Roger Pearse.
cleomedes, this, article, about, greek, astronomer, lunar, crater, crater, ancient, greek, boxer, kleomedes, astypalia, greek, Κλεομήδης, greek, astronomer, known, chiefly, book, circular, motions, celestial, bodies, Κυκλικὴ, θεωρία, μετεώρων, also, known, hea. This article is about the Greek astronomer For the lunar crater see Cleomedes crater For the Ancient Greek boxer see Kleomedes of Astypalia Cleomedes Greek Kleomhdhs was a Greek astronomer who is known chiefly for his book On the Circular Motions of the Celestial Bodies Kyklikὴ 8ewria metewrwn also known as The Heavens Latin Caelestia Contents 1 Placing his work chronologically 2 On the Circular Motions of the Celestial Bodies 3 Optics 4 Legacy 5 References 6 Further reading 7 External linksPlacing his work chronologically editHis birth and death dates are not known historians have suggested that he wrote his work sometime between the mid 1st century BC and 400 AD The earlier estimates rely on the fact that Cleomedes refers extensively in his writing to the work of mathematician and astronomer Posidonius of Rhodes c 135 c 51 BC and yet seemingly not at all to the work of Ptolemy c 100 c 170 AD Cleomedes also refers to Aristotle 384 322 BC Pytheas of Massalia 310 306 BC Aratus c 315 310 BC 240 BC Eratosthenes 276 195 BC and Hipparchus c 190 c 120 BC These conclusions have been challenged on the grounds that Cleomedes work was in relatively elementary astronomy and that reference to Ptolemy would not necessarily be expected The 20th century mathematician Otto Neugebauer however looked closely at the astronomical observations made by Cleomedes and concluded that a date of 371 AD 50 years better explains what is found there Neugebauer s estimate has been challenged on the grounds that Cleomedes makes observational errors with enough frequency that there is difficulty in deciding which observations to trust for the purpose of dating his work On the Circular Motions of the Celestial Bodies editThe book for which Cleomedes is known is a fairly basic astronomy textbook in two volumes His purpose in writing seems to have been as philosophical as it was scientific he spends an extensive amount of time criticizing the scientific ideas of the Epicureans Cleomedes book is valued primarily for preserving apparently verbatim much of Posidonius writings on astronomy none of Posidonius books have survived to the modern day Cleomedes is accurate in some of his remarks on lunar eclipses especially his conjecture that the shadow on the Moon suggests a spherical Earth He also remarks presciently that the absolute size of many stars may exceed that of the Sun and that the Earth might appear as a very small star if viewed from the surface of the Sun This book is the original source for the well known story of how Eratosthenes measured the Earth s circumference Many modern mathematicians and astronomers believe the description to be reasonable and believe Eratosthenes achievement to be one of the more impressive accomplishments of ancient astronomy Cleomedes deserves credit for the earliest clear statement of the apparent distance explanation of the Sun Illusion or Moon Illusion He argued that the sun appeared farther away on the horizon than in the zenith and therefore larger since its angular size was constant He attributed this explanation to Posidonius Optics editAs a disciple of Posidonius Cleomedes noted some elementary qualitative properties of refraction such as the bending of a ray toward the perpendicular in passing from a less dense to a more dense medium and suggested that due to atmospheric refraction the Sun and its rainbow may be visible when the Sun is below the horizon 1 Legacy editCleomedes is now memorialized by the crater Cleomedes in the northeastern portion of the visible Moon References edit Carl Benjamin Boyer The Rainbow From Myth to Mathematics 1959 Further reading editAlan C Bowen Robert B Todd Cleomedes Lectures on Astronomy A Translation of The Heavens with an Introduction and Commentary University of California Press 2004 ISBN 0520233255 Helen E Ross Cleomedes c 1st century AD on the celestial illusion atmospheric enlargement and size distance invariance Perception 2000 29 863 871 External links editOn the Circular Motions of the Celestial Bodies original text online and biography English translation of the section on Eratosthenes and the size of the earth at Roger Pearse O Connor John J Robertson Edmund F Cleomedes MacTutor History of Mathematics Archive University of St Andrews An article on Cleomedes description of atmospheric enlargement from Perception 2000 Edicion Bilingue Griego Espanol Retrieved from https en wikipedia org w index php title Cleomedes amp oldid 1135701777, wikipedia, wiki, book, books, library,
