Editing Ptolemy (section)

=== ''Planetary Hypotheses'' ===
[[File:Bartolomeu Velho 1568.jpg|thumb|upright=1.1|A depiction of the non-Ptolemaic Universe with no epicycles, possibly from 500 years before Ptolemy, as described in the ''Planetary Hypotheses'' by [[Bartolomeu Velho]] (1568).]]
The ''Planetary Hypotheses'' ({{Langx|el|Ὑποθέσεις τῶν πλανωμένων}}, {{Lit|Hypotheses of the Planets}}) is a [[Cosmology|cosmological]] work, probably one of the last written by Ptolemy, in two books dealing with the structure of the universe and the laws that govern [[Celestial mechanics|celestial motion]].<ref>
{{cite journal
 |last=Murschel |first=A.
 |year=1995
 |title=The structure and function of Ptolemy's physical hypotheses of planetary motion
 |journal=[[Journal for the History of Astronomy]]
 |volume=26  |issue=1  |pages=33–61
 |doi=10.1177/002182869502600102
 |bibcode=1995JHA....26...33M  |s2cid=116006562
}}
</ref>
Ptolemy goes beyond the mathematical models of the ''Almagest'' to present a physical realization of the universe as a set of nested spheres,<ref>
{{cite web
 |first=Dennis |last=Duke
 |title=Ptolemy's cosmology
 |website= scs.fsu.edu/~dduke  |type=academic pers. website
 |publisher=[[Florida State University]]
 |url=http://people.scs.fsu.edu/~dduke/ptolemy.html
 |url-status=dead
 |archive-url=https://web.archive.org/web/20091107202956/http://people.sc.fsu.edu/~dduke/ptolemy.html
 |archive-date=2009-11-07
}} — Cited page seems to present for viewing some alternate version of the now defunct [[Shockwave Flash]] video file format. The video file ''player'' software for the file has been "retired" and delibarately disabled / shut down / blocked / by [[Adobe Inc.|Adobe]]. The file is still present, embedded in the archived web page's source, and with only a little extra effort can be extracted from the copy saved in the Internet Archive, linked to in the citation.
</ref>
in which he used the [[epicycle]]s of his planetary model to compute the dimensions of the universe. He estimated the Sun was at an average distance of {{nobr|{{gaps|1|210}} Earth radii}} (now known to actually be {{nobr|{{gaps|~23|450}} radii),}} while the radius of the sphere of the fixed stars was {{nobr|{{gaps|20|000}} times}} the radius of the Earth.<ref>
{{cite journal
 |first=Bernard R. |last=Goldstein
 |year=1967
 |title=The Arabic version of Ptolemy's planetary hypotheses
 |journal=[[Transactions of the American Philosophical Society]]
 |volume=57 |number=4 |pages=9–12
|doi=10.2307/1006040
 |jstor=1006040
 }}
</ref>

The work is also notable for having descriptions on how to build instruments to depict the planets and their movements from a [[Geocentric model|geocentric]] perspective, much as an [[orrery]] would have done for a [[Heliocentrism|heliocentric]] one, presumably for didactic purposes.<ref>
{{cite journal
 |last=Hamm |first=E.
 |year=2016
 |title=Modeling the heavens: Sphairopoiia and Ptolemy's planetary hypotheses
 |url=https://doi.org/10.1162/POSC_a_00214
 |journal=[[Perspectives on Science]]
 |volume=24 |issue=4 |pages=416–424
 |doi=10.1162/POSC_a_00214 |s2cid=57560804
}}
</ref>