Armillary sphere
An armillary sphere is a model of objects in the sky, consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic. As such, it differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations. It was invented separately, in ancient China possibly as early as the 4th century BC and ancient Greece during the 3rd century BC, with later uses in the Islamic world and Medieval Europe.
With the Earth as center, an armillary sphere is known as Ptolemaic. With the Sun as center, it is known as Copernican.
The flag of Portugal features an armillary sphere. The armillary sphere is also featured in Portuguese heraldry, associated with the Portuguese discoveries during the Age of Exploration. Manuel I of Portugal, for example, took it as one of his symbols where it appeared on his standard, and on early Chinese export ceramics made for the Portuguese court. In the flag of the Empire of Brazil, the armillary sphere is also featured.
The Beijing Capital International Airport Terminal 3 features a large armillary sphere metal sculpture as an exhibit of Chinese inventions for international and domestic visitors.
Description and use
The exterior parts of this machine are a compages of brass rings, which represent the principal circles of the heavens:- The equinoctial A, which is divided into 360 degrees for showing the sun's right ascension in degrees; and also into 24 hours, for showing its right ascension in time.
- The ecliptic B, which is divided into 12 signs, and each sign into 30 degrees, and also into the months and days of the year, in such a manner that the degree or point of the ecliptic on which the sun appears, on any given day, stands over that day in the circle of months.
- The tropic of Cancer C, touching the ecliptic at the beginning of Cancer in e, and the tropic of Capricorn D, touching the ecliptic at the beginning of Capricorn in f; each circle 23 degrees from the equinoctial circle.
- The Arctic Circle E, and the Antarctic Circle F, each circle 23 degrees from its respective pole at N and S.
- The equinoctial colure G, passing through the north and south poles of the heavens at N and S, and through the equinoctial points in Aries and Libra, in the ecliptic.
- The solstitial colure H, passing through the poles of the heavens, and through the solstitial points in Cancer and Capricorn, in the ecliptic. Each quarter of the equinoctial colure is divided into 90 degrees, from the equinoctial to the poles of the world, for showing the declination of the sun, moon, and stars; and each quarter of the solstitial colure, from the ecliptic as e and f, to its poles b and d, for showing the latitude of the stars.
Within these circular rings is a small terrestrial globe I, fixed on an axis K, which extends from the north and south poles of the globe at n and s, to those of the celestial sphere at N and S. On this axis the flat celestial meridian L is fixed, which may be set directly over the meridian of any place on the globe, so as to keep over the same meridian upon it. This flat meridian is graduated the same way as the brass meridian of the common globe, and its use is much the same.
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 equator, which is a movable 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 horizon is divided into 360 degrees all around its outermost edge, within which are the points of the compass, for showing the amplitude of the sun and the moon, both in degrees and points. The celestial meridian L passes through two notches in the north and south points of the horizon, as in a common globe: if the globe is turned around, the horizon and meridian turn with it. At the south pole of the sphere is a circle of 25 hours, fixed to the rings. On the axis is an index which goes around that circle, if the globe is turned around its axis.
File:Clock Tower from Su Song's Book desmear.JPG|thumb|upright|The original diagram of Chinese scientist Su Song's book of 1092 showing the inner workings of his clocktower; a mechanically rotated armillary sphere crowns the top.
The globe assembly 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. The globe assembly 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 and two pinions, whose axes come out at V and U; either of which may be turned by the small winch W. When the winch is put upon the axis V, and turned 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; showing that they rise and set in the same points of the horizon, and at the same times in the hour circle, whether the motion be in the earth or in the heaven. If the earthly globe be turned, the hour-index goes round its hour-circle; but if the sphere be turned, the hour-circle goes round below the index.
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 heavens.
To reset the sphere for use, one must first slacken the screw r in 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 lies at the side of the stem R; then the axis of the sphere will be properly elevated, so as to stand parallel to the axis of the terrestrial globe, if the globe assembly is to be aligned to north and south by a small compass: once this is done, the user must 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. The user then must turn the nut b until the sun Y comes to the given day of the year in the ecliptic, and the sun will be at its proper place for that day.
To find the place of the moon's ascending node, and also the place of the moon, an ephemeris must be consulted to set them right accordingly. Lastly, the user must turn the winch W, until either the sun comes to the meridian L, or until the meridian comes to the sun, and then set the hour-index to the XII, marked noon, the whole sphere will be reset. Then the user must turn the winch, and observe when the sun or moon rises and sets in the horizon. The hour-index will show the times thereof for the given day.
History
China
Throughout Chinese history, astronomers have created celestial globes to assist the observation of the stars. The Chinese also used the armillary sphere in aiding calendrical computations and calculations.According to Joseph Needham, the earliest development of the armillary sphere in China goes back to the astronomers Shi Shen and Gan De in the 4th century BC, as they were equipped with a primitive single-ring armillary instrument. This would have allowed them to measure the north polar distance a measurement that gave the position in a xiu. Needham's 4th century BC dating, however, is rejected by British sinologist Christopher Cullen, who traces the beginnings of these devices to the 1st century BC.
During the Western Han dynasty additional developments made by the astronomers Luoxia Hong, Xiangyu Wangren, and Geng Shouchang advanced the use of the armillary in its early stage of evolution. In 52 BC, it was the astronomer Geng Shouchang who introduced the first permanently fixed equatorial ring of the armillary sphere. In the subsequent Eastern Han dynasty period, the astronomers Fu An and Jia Kui added the ecliptic ring by 84 AD. With the famous statesman, astronomer, and inventor Zhang Heng, the sphere was totally complete in 125 AD, with horizon and meridian rings. The world's first water-powered celestial globe was created by Zhang Heng, who operated his armillary sphere by use of an inflow clepsydra clock.
Subsequent developments were made after the Han dynasty that improved the use of the armillary sphere. In 323 AD the Chinese astronomer Kong Ting was able to reorganize the arrangement of rings on the armillary sphere so that the ecliptic ring could be pegged on to the equator at any point desired. The Chinese astronomer and mathematician Li Chunfeng of the Tang dynasty created one in 633 AD with three spherical layers to calibrate multiple aspects of astronomical observations, calling them 'nests'. He was also responsible for proposing a plan of having a sighting tube mounted ecliptically in order for the better observation of celestial latitudes. However, it was the Tang Chinese astronomer, mathematician, and monk Yi Xing in the next century who would accomplish this addition to the model of the armillary sphere. Ecliptical mountings of this sort were found on the armillary instruments of Zhou Cong and Shu Yijian in 1050, as well as Shen Kuo's armillary sphere of the later 11th century, but after that point they were no longer employed on Chinese armillary instruments until the arrival of the European Jesuits.
Image:ChineseCelestialGlobe.JPG|thumbnail|upright|Celestial globe from the Qing dynasty
In 723 AD, Yi Xing and government official Liang Ling-zan combined Zhang Heng's water powered celestial globe with an escapement device. With drums hit every quarter-hour and bells rung automatically every full hour, the device was also a striking clock. The famous clock tower that the Chinese polymath Su Song built by 1094 during the Song dynasty would employ Yi Xing's escapement with waterwheel scoops filled by clepsydra drip, and powered a crowning armillary sphere, a central celestial globe, and mechanically operated manikins that would exit mechanically opened doors of the clock tower at specific times to ring bells and gongs to announce the time, or to hold plaques announcing special times of the day. There was also the scientist and statesman Shen Kuo. Being the head official for the Bureau of Astronomy, Shen Kuo was an avid scholar of astronomy, and improved the designs of several astronomical instruments: the gnomon, armillary sphere, clepsydra clock, and sighting tube fixed to observe the pole star indefinitely. When Jamal al-Din of Bukhara was asked to set up an 'Islamic Astronomical Institution' in Khubilai Khan's new capital during the Yuan dynasty, he commissioned a number of astronomical instruments, including an armillary sphere. It was noted that "Chinese astronomers had been building since at least 1092".