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 British Museum has a collection of several armillary sphere rings that are incredibly well-crafted and detailed. When closed, they look like any other ring, but as the different bands are fanned out, the rings take on a unique quality. Built with anywhere between two to eight moving bands, these intricate pieces of jewelry would need to have been executed by skilled craftsmen. The armillary sphere is commonly used in heraldry and vexillology, being mainly known as a symbol associated with Portugal, the Portuguese Empire and the Portuguese discoveries.

Suspended within a ring the sphere sits in a cradle which is mounted on an elegant tripod stand. The position of the ring can be adjusted for latitude within the cradle. At the top of the stand is another ring representing the celestial horizon. As the sphere rotates, anything above the horizon ring at any one time will, in theory, be visible in the heavens; anything below, will be hidden. I think what’s most interesting (to me anyway) about these rings is the fact that they were, for some, important tools to grasp advanced concepts of astronomy, but for others, they were almost a way to brag about their own accomplishments. I mean, being an astronomer several centuries ago surely took plenty of work and a whole lot of learning (as is still true today), but scientists aren’t typically known for being braggadocious. Historians disagree about the origin and the use of demonstrational armillary spheres, partly because the available evidence is difficult to interpret.In Renaissance Europe, the armillary sphere was amongst the first complex mechanical devices. Public figures often had their portraits painted showing them with one hand on an armillary sphere which represented the height of wisdom and knowledge. The solstitial colure H, passing through the poles of the heaven, and through the solstitial points Cancer and Capricorn, in the ecliptic. Each quarter of the former of these colures 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 latter, from the ecliptic as e and f, to its poles b and d, for showing the latitude of the stars. An armillary sphere is ideally suited as a sundial. With its hour face inscribed on the inner circular surface of the Equatorial ring—also known as the Equinoctial—the gnomon’s shadow sweeps uniformly along with time, allowing the hour markings to be equally spaced along the equinoctial ring. 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.

The metal rings, usually made of brass or bronze, are referred to as armilla, which is Latin for bracelet. Armilla were prestigious armbands awarded to Roman soldiers for distinguished gallantry.

Used by astronomers to study and make calculations, these pieces of jewelry were considered tokens of knowledge.

Horizon: in astronomy, the unobstructed horizon is the circumference of the plane tangent to the earth’s surface at the observer’s location that intersects the celestial sphere. The horizon’s altitude is 0 o. At the centre of the sphere is the Earth. As the Earth is stationary in this model, it is the celestial sphere which rotates about it and acts as a reference system for locating the celestial bodies – stars, in particular – from a geocentric perspective. An armillary sphere such as this one might well have been used for education, aiding understanding of the 3-dimensional geometry of the celestial sphere. This makes sense, as many medieval and early-modern texts in basic astronomy refer to or assume the use of armillaries as models of the heavens. Medieval illustrations even suggest that a 3-dimensional visual aid might well have been a necessary companion to texts on the celestial sphere, such as the 13th-century De sphaera by Sacrobosco, which was a widely used university textbook.

Armillary spheres existed in Greece and China as early as the 4 th Century BC. Mechanical versions were later introduced with moveable horizon rings and other features such as a positionable sun. As one of the first planetarium devices, the mechanical armillary sphere was used both for astronomical observations and teaching purposes. Great Circle: a largest circle along the surface of a sphere, whose center coincides with the center of the sphere. Williams, Henry Smith (2004). A History Of Science. Whitefish, MT: Kessinger Publishing. ISBN 1-4191-0163-3. The Arctic Circle E, and the Antarctic Circle F, each 23 1⁄ 2 degrees from its respective pole at N and S.

The armillary sphere was reintroduced in the national arms and in the national Flag of Portugal in 1911. Kern, Ralf: Wissenschaftliche Instrumente in ihrer Zeit. Vom 15. – 19. Jahrhundert. Verlag der Buchhandlung Walther König 2010, ISBN 978-3-86560-772-0 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. Equinoctial: refers to the celestial equator. The term equinoctial refers to the fact that the vernal and autumnal equinoxes occur when the sun passes through this great circle. The celestial equator is a projector of the earth’s equator onto the celestial sphere. The hour markings of the armillary sundial are inscribed on the inner surface of this ring. The Sphere was not included in the photographic inventory of Griffiths' collection in 1930 so may have been acquired after that date. Its earlier provenance is unknown.

The nomenclature of an armillary sphere is based on the terminology of the following astronomical coordinate systems (see table below). In the end of the 15th century, the armillary sphere became the personal heraldic badge of the future King Manuel I of Portugal, when he was still a Prince. The intense use of this badge in documents, monuments, flags and other supports, during the reign of Manuel I, transformed the armillary sphere from a simple personal symbol to a national one that represented the Kingdom of Portugal and in particular its Overseas Empire. As a national symbol, the armillary sphere continued in use after the death of Manuel I.Arctic Circle: This small circle forms the northernmost latitude on earth at which the center of the sun’s disk travels completely around the horizon for a full 24 hours on the June solstice (summer solstice in the Northern hemisphere). Currently the latitude of the Arctic Circleis 66 o 33.8’ N.The latitude of the Arctic Circlevaries from67.9 o N and 65.5 o Nover about 41,000 years. The Arctic Circleis moving south toward the equator at about 50 feet per year. Zenith: in the horizon coordinate system, it is the position directly overhead on the celestial sphere. The zenith’s altitude is 90 o.