Editing Hipparchus (section)

==Geography==
Hipparchus's treatise ''Against the Geography of Eratosthenes'' in three books is not preserved.<ref>Editions of fragments: {{harvnb|Berger|1869}} (Latin), {{harvnb|Dicks|1960}} (English).</ref> 
Most of our knowledge of it comes from [[Strabo]], according to whom Hipparchus thoroughly and often unfairly criticized [[Eratosthenes]], mainly for internal contradictions and inaccuracy in determining positions of geographical localities. Hipparchus insists that a geographic map must be based only on astronomical measurements of [[Latitude and longitude|latitudes and longitudes]] and [[triangulation]] for finding unknown distances. 
In geographic theory and methods Hipparchus introduced three main innovations.<ref>On Hipparchus's geography see: {{harvnb|Berger|1869}}; {{harvnb|Dicks|1960}}; {{harvnb|Neugebauer|1975|loc=[https://archive.org/details/historyofancient0000neug/page/332/ {{pgs|332–338}}]}}; {{harvnb|Shcheglov|2007}}.</ref>

He was the first to use the [[Geographic coordinate system|grade grid]], to determine [[Latitude|geographic latitude]] from star observations, and not only from the Sun's altitude, a method known long before him, and to suggest that [[Longitude|geographic longitude]] could be determined by means of simultaneous observations of lunar eclipses in distant places. In the practical part of his work, the so-called "table of [[Clime|climata]]", Hipparchus listed latitudes for several tens of localities. In particular, he improved [[Eratosthenes]]' values for the latitudes of [[Athens]], [[Sicily]], and [[Comorin|southern extremity of India]].{{r|shcheglov2010}}{{r|shcheglov2006}}{{sfn|Shcheglov|2007}} In calculating latitudes of [[clime|climata]] (latitudes correlated with the length of the longest solstitial day), Hipparchus used an unexpectedly accurate value for [[Axial tilt|the obliquity of the ecliptic]], 23°40' (the actual value in the second half of the second century&nbsp;BC was approximately 23°43'), whereas all other ancient authors knew only a roughly rounded value 24°, and even [[Ptolemy]] used a less accurate value, 23°51'.<ref>Diller A. (1934). "Geographical Latitudes in Eratosthenes, Hipparchus and Posidonius". ''Klio'' 27.3: 258–269; cf. {{harvnb|Shcheglov|2007|pages=177–180}}.</ref>

Hipparchus opposed the view generally accepted in the [[Hellenistic period]] that the [[Atlantic Ocean|Atlantic]] and [[Indian Ocean]]s and the [[Caspian Sea]] are parts of a single ocean. At the same time he extends the limits of the [[Ecumene|oikoumene]], i.e. the inhabited part of the land, up to the [[equator]] and the [[Arctic Circle]].{{r|shcheglov2007-thule}} Hipparchus's ideas found their reflection in the ''[[Geography (Ptolemy)|Geography]]'' of [[Ptolemy]]. In essence, Ptolemy's work is an extended attempt to realize Hipparchus's vision of what geography ought to be.