The ''Planisphaerium'' is a work by

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

. The title can be translated as "celestial plane" or "star chart". In this work Ptolemy explored the mathematics of mapping figures inscribed in the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

onto a plane by what is now known as

stereographic projection In mathematics, a stereographic projection is a perspective transform, perspective projection of the sphere, through a specific point (geometry), point on the sphere (the ''pole'' or ''center of projection''), onto a plane (geometry), plane (th ...

. This method of projection preserves the properties of circles.

Publication

Originally written in

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

, ''Planisphaerium'' was one of many scientific works which survived from antiquity in

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

translation. One reason why ''Planisphaerium'' attracted interest was that stereographic projection was the mathematical basis of the plane astrolabe, an instrument which was widely used in the medieval Islamic world. The

Suda The ''Suda'' or ''Souda'' (; ; ) is a large 10th-century Byzantine Empire, Byzantine encyclopedia of the History of the Mediterranean region, ancient Mediterranean world, formerly attributed to an author called Soudas () or Souidas (). It is an ...

lists a work of Ptolemy titled ''Simplification of the Sphere'' () which is presumed to be ''Planisphaerium''. In 1143 the work was translated from Arabic into Latin by

Herman of Carinthia Herman of Carinthia (1105/1110 – after 1154), also called Hermanus Dalmata or Sclavus Dalmata, Secundus, by his own words born in the "heart of Istria", was a philosopher, astronomer, astrologer, mathematician and translator of Arabic works int ...

, who also translated commentaries by Maslamah Ibn Ahmad al-Majriti. The oldest known translation is in Arabic done by an unknown scholar as part of the Translation Movement in

Baghdad Baghdad ( or ; , ) is the capital and List of largest cities of Iraq, largest city of Iraq, located along the Tigris in the central part of the country. With a population exceeding 7 million, it ranks among the List of largest cities in the A ...

Planisphere

The word planisphere (Latin planisphaerium) was originally used in the second century by Ptolemy to describe the representation of a spherical Earth by a map drawn in the plane. Journal of the British Astronomical Association yr:1995 pg:35 * Planisphere

Editions and translations

References

External links

"Ptolemy on Astrolabes"
Ancient Greek mathematical works Astronomy books Works by Ptolemy {{math-hist-stub