Editing Hipparchus (section)

==Babylonian sources==
{{further|Babylonian astronomy}}
Earlier Greek astronomers and mathematicians were influenced by Babylonian astronomy to some extent, for instance the period relations of the [[Metonic cycle]] and [[Saros cycle]] may have come from Babylonian sources (see "[[Babylonian astronomical diaries]]"). Hipparchus seems to have been the first to exploit Babylonian astronomical knowledge and techniques systematically.{{r|toomer1988}} Eudoxus in the 4th century BC and [[Timocharis]] and [[Aristillus]] in the 3rd century BC already divided the ecliptic in 360 parts (our [[degree (angle)|degrees]], Greek: moira) of 60 [[arcminutes]] and Hipparchus continued this tradition. It was only in Hipparchus's time (2nd century BC) when this division was introduced (probably by Hipparchus's contemporary [[Hypsicles]]) for all circles in mathematics. [[Eratosthenes]] (3rd century BC), in contrast, used a simpler [[sexagesimal]] system dividing a circle into 60 parts. Hipparchus also adopted the Babylonian astronomical ''[[cubit]]'' unit ([[Akkadian language|Akkadian]] ''ammatu'', Greek πῆχυς ''pēchys'') that was equivalent to 2° or 2.5° ('large cubit').{{r|bg1991}}

Hipparchus probably compiled a list of Babylonian astronomical observations; [[Gerald J. Toomer]], a historian of astronomy, has suggested that Ptolemy's knowledge of eclipse records and other Babylonian observations in the ''Almagest'' came from a list made by Hipparchus. Hipparchus's use of Babylonian sources has always been known in a general way, because of Ptolemy's statements, but the only text by Hipparchus that survives does not provide sufficient information to decide whether Hipparchus's knowledge (such as his usage of the units cubit and finger, degrees and minutes, or the concept of hour stars) was based on Babylonian practice.{{r|hoffman-befunde}} However, [[Franz Xaver Kugler]] demonstrated that the synodic and anomalistic periods that Ptolemy attributes to Hipparchus had already been used in Babylonian [[ephemerides]], specifically the collection of texts nowadays called "System B" (sometimes attributed to [[Kidinnu]]).{{r|kugler1900}}{{pages needed|date=April 2023}}

Hipparchus's long [[orbital period|draconitic]] lunar period (5,458 months = 5,923 lunar nodal periods) also appears a few times in [[Babylonian astronomy|Babylonian records]].{{r|aaboe1955}} But the only such tablet explicitly dated, is post-Hipparchus so the direction of transmission is not settled by the tablets.