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Further information: Planetarium and Antikythera mechanism Ptolemy with an armillary sphere model, by Joos van Ghent and Pedro Berruguete, 1476, Louvre, Paris The armillary sphere survives as useful for teaching, and may be described as a skeleton celestial globe, the series of rings representing the great circles of the heavens, and revolving on an axis within a horizon. With the earth as center such a sphere is known as Ptolemaic; with the sun as center, as Copernican. [1] When the shadow of the rings are aligned so that they appear to be in the same, or nearly the same, place, the meridian identifies itself. [ clarification needed] Meridional ring [ edit ] The Greek astronomer Hipparchus ( c. 190– c. 120 BC) credited Eratosthenes (276–194 BC) as the inventor of the armillary sphere. [11] [12] [13] [14] [15] Names of this device in Greek include ἀστρολάβος astrolabos and κρικωτὴ σφαῖρα krikōtē sphaira "ringed sphere". [16] The English name of this device comes ultimately from the Latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking the poles and representing the equator, the ecliptic, meridians and parallels. Usually a ball representing the Earth or, later, the Sun is placed in its center. It is used to demonstrate the motion of the stars around the Earth. Before the advent of the European telescope in the 17th century, the armillary sphere was the prime instrument of all astronomers in determining celestial positions.

Further advances in this instrument were made by Danish astronomer Tycho Brahe (1546–1601), who constructed three large armillary spheres which he used for highly precise measurements of the positions of the stars and planets. They were described in his Astronomiae Instauratae Mechanica. [25]

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Others have been found to be engraved with two twelve-hour time scales. Each twelve-hour scale is stretched over 180 degrees and numbered by hour with hashes every 20 minutes and smaller hashes every four minutes. The inside displays a calendrical scale with the names of the months indicated by their first letters, with a mark to show every 5 days and other marks to represent single days. On these, the outside of the ring is engraved with the corresponding symbols of the zodiac signs. The position of the symbol indicates the date of the entry of the sun into this particular sign. The vernal equinox is marked at March 15 and the autumnal equinox is marked at September 10. [7] Declination ring [ edit ] Astronomical ring with an alidade on the declination ring (folded closed). Armillary spheres were among the first complex mechanical devices. Their development led to many improvements in techniques and design of all mechanical devices. Renaissance scientists and public figures often had their portraits painted showing them with one hand on an armillary sphere, which represented the zenith of wisdom and knowledge. Since ancient times, astronomers around the world have used models of the sky to make calculations. With the advent of the armillary sphere, stargazers were given a physical model to better visualize the lines of celestial longitude and latitude. Created independently in ancient Greece and ancient China, these armillary spheres consisted of spherical rings centered on either the Earth or the Sun. During the 16th and 17th centuries, these astronomy tools were sized down to become fashionable finger rings that moved just like regular armillary spheres.

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. The meridian ring is placed vertically, then rotated (relative to the celestial object) until it is parallel to the local north-south line. The whole ring is thus parallel to the circle of longitude passing through the place where the user is standing. In 1610, Edward Wright created the sea ring, which mounted a universal ring dial over a magnetic compass. This permitted mariners to determine the time and magnetic variation in a single step. [4] These are also called "sundial compasses".Throughout Chinese history, astronomers have created celestial globes ( Chinese: 渾象) to assist the observation of the stars. The Chinese also used the armillary sphere in aiding calendrical computations and calculations. 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 23 1⁄ 2 degrees from the equinoctial circle. An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), 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. The equinoctial colure G, passing through the north and south poles of the heaven at N and S, and through the equinoctial points Aries and Libra, in the ecliptic. The Arctic Circle E, and the Antarctic Circle F, each 23 1⁄ 2 degrees from its respective pole at N and S.