Celestial globes were used to represent the stars and constellations of the night sky and record their positions with respect to each other and a co-ordinate system. They were also used as analogue computers to resolve problems involving the stars (Starry Messanger).
In the most common form of celestial globe, a number of stars were marked on a sphere, and the constellation figures sketched. The sphere was mounted by its poles on a metal circle. The ecliptic and equator were marked and divided on the globe, to measure celestial longitude and right ascension. Declination was measured using divisions marked on the meridian. The globe was placed in a stand, which included a broad horizontal band, known as the horizon.
The elevation of the pole of the globe above the horizon could be varied to adjust for the user's latitude. Since the ecliptic and equator are marked, the globe could be used to work out the times of rising and setting of the stars, or the time of their highest point in the sky (Starry Messanger). Celestial globes show the apparent positions of the stars in the sky. They omit the Sun, Moon and planets because the positions of these bodies vary relative to those of the stars, but the ecliptic, along which the Sun moves, is indicated. A potential issue arises regarding the 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 back-to-front on the surface of the globe. This is because the view from Earth, positioned at the centre of the celestial sphere, is of the inside of the celestial sphere, whereas the celestial globe is viewed from the outside. For this reason, celestial globes may be produced in mirror image, so that at least the constellations appear the right way round (Celestial Sphere). The celestial sphere is divided by mentally projecting the equator into space, and then having the equatorial line act as the divide for two hemispheres that separate the sphere. Just as the earth rotates once on its axis, so does the celestial sphere, however, the difference between the celestials sphere and the earth is that the earth rotates from east to west the celestial sphere rotates from west to east (Celestial Sphere). A globe is a three-dimensional scale model of Earth (terrestrial globe or geographical globe) or other celestial body such as a planet, star, or moon.
While models can be made of objects with arbitrary or irregular shapes, the term globe is used only for models of objects that are approximately spherical. The word 'globe' comes from the Latin word globus, meaning round mass or sphere. Some terrestrial globes include relief to show mountains and other features on the Earth's surface (Hudson) Celestial Globe Tres Zenchuk The sphericity of the Earth was established by Greek astronomy in the 3rd century BC, and the earliest terrestrial globe appeared from that period. The earliest known example is the one constructed by Crates of Mallus in Cilicia,in the mid-2nd century BC.(Hudson) Works Cited Celestial. Digital image. Digital image. 'The Celestial Globe.'
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