A celestial globe, first used by the Greek astronomers, in which the sky is represented by a skeleton framework of intersecting circles, the Earth being at the centre. In antiquity, it was of major importance for measuring star positions. The first Chinese sphere dates from the 4th-c BC; they had a 20-ton sphere in the 11th-c.
An armillary sphere (variations known as a spherical astrolabe, armilla, or armil) is a model of the celestial sphere, invented by Eratosthenes in 255 BC. When several rings or circles were combined representing the great circles of the heavens, the instrument became an armillary sphere. i.), and it is of great interest as an example of the armillary sphere passing into the spherical astrolabe.
Armillary spheres were developed by the Greeks and were used as teaching tools already in the 3rd century B.C..
Renaissance scientists and public figures often had their portraits painted showing them with one hand on an armillary sphere, which represented the height of wisdom and knowledge.
Armillary spheres were among the first complex mechanical devices.
The armillary sphere survives as useful for teaching, and may be described as a skeleton celestial globe, the series of ring srepresenting the great circles of the heavens, and revolving on an axis within a horizon.
A representation of an armillary sphere is present in the modern flag of Portugal and has been a national symbol since the reign of Manuel I.
The description and use of the armillary sphere
The exterior parts of this machine are a compages of brass rings, which represent the principal circles of the heaven.
In the north pole of the ecliptic is a nut b, to which is fixed one end of the quadrantal wire, and to the other end a small sun Ψ, which is carried round the ecliptic B—B, by turning the nut : and in the south pole of the ecliptic is a pin d, on which is another quadrantal wire, with a small moon Ζ upon it, which may be moved round by hand : but there is a particular contrivance for causing the moon to move in an orbit which crosses the ecliptic at an angle of 5⅓ degrees, in to opposite points called the moon's nodes;
Within these circular rings is a small terrestrial globe J, fixed on an axis K, which extends from the north and south poles of the globe at n and s, to those of the celestrial sphere at N and S. On this axis is fixt the flat celestial meridian L L, which may be set directly over the meridian of any place on the globe, so as to keep over the same meridian upon it. To this globe is fitted the movable horizon M, so as to turn upon the two strong wires proceeding from its east and west points to the globe, and entering the globe at the opposite points off its equattor, which is a moveable brass ring set into the globe in a groove all around its equator. The globe may be turned by hand within this ring, so as to place any given meridian upon it, directly under the celestial meridian L. The celestrial meridian L passes through two notches in the north and south points of the horizon, as in a common globe: buth here, if the globe be turned round, the horizon and meridian turn with it. At the south pole of the sphere is a circle of 25 hours, fixt to the rings, and on the asix is an index which goes round that circle, if the clobe be turned round its axis.
The whole fabric is supported on a pedestal N, and may be elevated or depressed upon the joint O, to any number of degrees from 0 to 90, by means of the arc P, which is fixed in the strong brass arm Q, and slides in the upright piece R, in which is a screw at r, to fix it at any proper elevation.
In the box T are two wheels (as in Dr Long's sphere) and two pinions, whose axes come out at V and U; When the winch is put upon the axis V, and turn backward, the terrestrial globe, with its horizon and celestial meridian, keep at rest; and the whole sphere of circles turns round from east, by south, to west, carrying the sun Y, and moon Z, round the same way, and causing them to rise above and set below the horizon. But when the winch is put upon the axis U, and turned forward, the sphere with the sun and moon keep at rest; and the earth, with its horizon and meridian, turn round from horizon to the sun and moon, to which these bodies came when the earth kept at rest, and they were carried round it;
And so, by this construction, the machine is equally fitted to show either the real motion of the earth, or the apparent motion of the heaven.
To rectify the sphere for use, first slacken the screw rin the upright stem R, and taking hold of the arm Q, move it up or down until the given degree of latitude for any place be at the side of the stem R; and then the axis of the sphere will be properly elevated, so as to stand parallel to the axis of the world, if the machine be set north and south by a small compass: this done, count the latitude from the north pole, upon the celestial meridian L, down towards the north notch of the horizon, and set the horizon to that latitude; then, turn the nut b until the sun Y comes ot the given day of the year in the ecliptic, and the sun will be at its proper place for that day: find the place of the moon's ascending node, and also the place of the moon, by an Ephemeris, and set them right accordingly: lastly, turn the winch W, until either the sun comes to the meridian L, or until the meridian comes to the sun (according as you want the sphere or earth to move) and set the hour-index to the XXI, marked noon, and the whole machine will be rectified.
The earliest celestial globe was dated back to 52 BC in the West Han dynasty by the astronomers Geng Shou-chang (耿壽昌) and Luo-xia Hong (落下閎).
Then Li Chun-feng (李淳風) of the Tang dynasty created one in 633 AD with three spherical layers to calibrate multiple aspects of astronomical observations.
In 723 AD, Tang dynasty buddhist monk Yi-xing (一行) and government official Liang Ling-zan (梁令瓚) combined Zhang Heng's water powered celestial globe with an escapement device.
Jang Yeong-sil, a Korean inventor, was ordered by King Sejong the Great of Joseon to build an armillary sphere.
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