Editing Armillary sphere (section)

=== Hellenistic world and ancient Rome ===
{{further|Planetarium|Antikythera mechanism}}
[[File:Wall painting - armillary sphere - Stabiae (villa di San Marco) - Stabia MAdSLdO 2535 - 02.jpg|thumb|Mythological figures within an armillary sphere in a fragmentary fresco from [[Stabiae]], mid-1st century AD]]
The [[Greek astronomy|Greek astronomer]] [[Hipparchus]] ({{Circa|190|120 BC}}) credited [[Eratosthenes]] (276{{snd}}194 BC) as the inventor of the armillary sphere.<ref>Williams, p. 131</ref><ref>Walter William Bryant: ''[https://archive.org/details/AHistoryOfAstronomy/page/n33/mode/2up A History of Astronomy]'', 1907, p. 18</ref><ref>John Ferguson: ''Callimachus'', 1980, {{ISBN|978-0-8057-6431-4}}, p. 18</ref><ref>Henry C. King: ''The History of the Telescope'', 2003, {{ISBN|978-0-486-43265-6}}, p. 7</ref><ref>Dirk L. Couprie, Robert Hahn, Gerard Naddaf: ''Anaximander in Context: New Studies in the Origins of Greek Philosophy'', 2003, {{ISBN|978-0-7914-5537-1}}, p. 179</ref> Names of this device in Greek include {{lang|grc|ἀστρολάβος}} ''astrolabos'' and {{lang|grc|κρικωτὴ σφαῖρα}} ''krikōtē sphaira'' "ringed sphere".<ref>{{LSJ|a)strola/bos|ἀστρολάβος}}, {{LSJ|krikwto/s|κρικωτή|ref}}.</ref> The English name of this device comes ultimately from the [[Latin]] ''armilla'' (circle, bracelet), since it has a skeleton made of graduated metal circles linking the [[celestial pole|pole]]s and representing the [[equator]], the [[ecliptic]], [[meridian (astronomy)|meridians]] and [[Circle of latitude|parallel]]s. Usually a ball representing the [[Earth]] or, later, the [[Sun]] is placed in its center. It is used to demonstrate the [[celestial mechanics|motion]] of the [[star]]s around the Earth. Before the advent of the European [[telescope]] in the 17th century, the armillary sphere was the prime instrument of all astronomers in determining celestial positions.

[[File:Ptolemy 1476 with armillary sphere model.jpg|thumb|left|upright|''[[Ptolemy]] with an armillary sphere model'', by [[Joos van Ghent]] and [[Pedro Berruguete]], 1476, [[Louvre]], Paris]]
In its simplest form, consisting of a ring fixed in the plane of the equator, the ''armilla'' is one of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian. The first was an equinoctial, the second a solstitial armilla. Shadows were used as indices of the sun's positions, in combinations with angular divisions. When several rings or circles were combined representing the great circles of the heavens, the instrument became an armillary sphere.<ref name="EB1911"/>

Armillary spheres were developed by the [[Hellenistic civilization|Hellenistic Greeks]] and were used as teaching tools already in the 3rd century BC. In larger and more precise forms they were also used as observational instruments. However, the fully developed armillary sphere with nine circles perhaps did not exist until the mid-2nd century AD, during the [[Roman Empire]].<ref name="encyclopedia britannica armillary sphere"/> Eratosthenes most probably used a solstitial armilla for measuring the [[obliquity]] of the ecliptic. Hipparchus probably used an armillary sphere of four rings.<ref name="encyclopedia britannica armillary sphere">Editors of Encyclopædia Britannica. (16 November 2006). "[https://www.britannica.com/science/armillary-sphere Armillary Sphere]." ''[[Encyclopædia Britannica]]''. Accessed 14 October 2017.</ref> The [[Greco-Roman world|Greco-Roman]] geographer and astronomer [[Ptolemy]] ({{Circa|100|170 AD}}) describes his instrument, the ''astrolabon'', in his ''[[Almagest]]''.<ref name="encyclopedia britannica armillary sphere"/> It consisted of at least three rings, with a graduated circle inside of which another could slide, carrying two small tubes positioned opposite each other and supported by a vertical plumb-line.<ref name="EB1911"/><ref name="encyclopedia britannica armillary sphere"/>