Editing Celestial globe (section)

{{Short description|Star charts arranged on a globe}}
[[File:Celestial globe with clockwork MET DP237685.jpg|thumb|upright=1.2|Celestial globe with clockwork; 1579; partly gilded silver, gilded brass and steel; overall: {{convert|27.3|×|20.3|×|19.1|cm|abbr=on}}, diameter of the globe: {{convert|14|cm|abbr=on}}; from [[Vienna]]; [[Metropolitan Museum of Art]] (New York City)]]
[[File:Celestial globe MET DP-12901-001.jpg|thumb|Celestial globe; after 1621; paper, brass, oak and stained and light-colored wood; overall: {{convert|52.1|×|47.3|cm|abbr=on}}, diameter of the globe: {{convert|34|cm|abbr=on}}; from [[Amsterdam]]; Metropolitan Museum of Art]]
[[File:Mughal Celestial Globe.jpg|thumb|[[Mughal Empire|Mughal]] era Celestial Globe by [[Muhammad Saleh Thattvi]] c.1663<ref>{{Cite web |title=A CELESTIAL GLOBE, MADE BY MUGHAL ASTROLABIST MUHAMMAD SALIH OF THATTA, DATED 1074 AH/1663 AD |url=https://www.orientalartauctions.com/object/artothe30798-a-celestial-globe-made-by-mughal-astrolabist-muhammad-salih-of-thatta-dated-1074-ah-1663-ad |access-date=2024-06-18 |website=www.orientalartauctions.com}}</ref>]]
'''Celestial globes''' show the [[apparent place|apparent positions]] of the [[star]]s in the sky. They omit the [[Sun]], [[Moon]], and [[planet]]s because the positions of these bodies vary relative to those of the stars, but the [[ecliptic]], along which the Sun moves, is indicated.

There is an issue regarding the "[[chirality|handedness]]" of celestial globes. If the globe is constructed so that the stars are in the positions they actually occupy on the imaginary [[celestial sphere]], then the star field will appear reversed on the surface of the globe (all the constellations will appear as their mirror images). This is because the view from [[Earth]], positioned at the centre of the celestial sphere, is of the [[gnomonic projection]] inside of the celestial sphere, whereas the celestial globe is [[Orthographic projection (cartography)|orthographic projection]] as viewed from the outside. For this reason, celestial globes are often produced in mirror image, so that at least the [[constellation]]s appear as viewed from Earth. This ambiguity is famously evident in the astronomical ceiling of New York City's [[Grand Central Terminal#Ceiling|Grand Central Terminal]], whose inconsistency was deliberately left uncorrected though it was noticed shortly after installation.

Some modern celestial globes address this problem by making the surface of the globe [[transparency and translucency|transparent]]. The stars can then be placed in their proper positions and viewed through the globe, so that the view is of the inside of the celestial sphere. However, the proper position from which to view the sphere would be from its centre, but the viewer of a transparent globe must be outside it, far from its centre. Viewing the inside of the sphere from the outside, through its transparent surface, produces serious distortions. [[Opacity (optics)|Opaque]] celestial globes that are made with the constellations correctly placed, so they appear as mirror images when directly viewed from outside the globe, are often viewed in a mirror, so the constellations have their familiar appearances. Written material on the globe, e.g., constellation names, is printed in reverse, so it can easily be read in the mirror.

Before [[Nicolaus Copernicus|Copernicus]]'s 16th-century discovery that the [[Solar System]] is "[[Heliocentrism|heliocentric]] rather than [[Geocentric model|geocentric]] and [[Geostationary orbit|geostatic]]" (that the Earth orbits the Sun and not the other way around) "the stars have been commonly, though perhaps not universally, perceived as though attached to the inside of a hollow sphere enclosing and rotating about the earth".{{sfn|Savage-Smith|1985|page=3}}<ref>{{Cite book|last=Borchert|first=Donald M.|title=In Encyclopedia of Philosophy, 2nd ed.|publisher=Macmillan Reference|year=2006|pages=532–536}}</ref> Working under the incorrect assumption that the cosmos was geocentric the second-century Greek astronomer [[Ptolemy]] composed the [[Almagest]] in which "the movements of the planets could be accurately represented by means of techniques involving the use of epicycles, deferents, eccentrics (whereby planetary motion is conceived as circular with respect to a point displaced from Earth), and equants (a device that posits a constant angular rate of rotation with respect to a point displaced from Earth)".<ref name=":2">{{Cite book|last=Dewald|first=Jonathan|title=Encyclopedia of the Early Modern World|publisher=Charles Scribner's Sons|year=2004|pages=148–154}}</ref> Guided by these ideas astronomers of the Middle Ages, [[Muslims|Muslim]] and [[Christianity|Christian]] alike, created celestial globes to "represent in a model the arrangement and movement of the stars".<ref name=":2" /> In their most basic form celestial globes represent the stars as if the viewer were looking down upon the sky as a globe that surrounds the Earth.