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There is no evidence for the Hellenistic origin of the spherical astrolabe, but rather evidence so far available suggests that it may have been an early but distinctly Islamic development with no Greek antecedents."

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. 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. Brashear, Ronald (May 1999). "Astronomiæ instauratæ mechanica by Tycho Brahe: Introduction". Special Collections Department. Smithsonian Institution Libraries . Retrieved July 11, 2020.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.

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. It wasn’t until the middle of the 1500s CE that the basis of the instrument – a geocentric concept of the Universe – was seriously challenged by the Polish mathematician Nicolaus Copernicus. Even then, the instrument still continued to serve a useful purpose as a purely mathematical instrument. How does an armillary sphere work? A beautiful object called an armillary sphere appears mysteriously in the gardens of the sisters’ home on Lake Geneva and plays a key role in The Seven Sisters series. 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. Tropic of Cancer: This small circle (also called the Northern Tropic) forms the northernmost latitude on earth at which the noontime sun can cross the zenith. This occurs around June 21 and is called the summer solstice in the northern hemisphere. A corresponding circle, also called the Tropic of Cancer, is formed by the projection of the earth’s Tropic of Cancer onto the celestial sphere. In ancient times, the sun passed through the zodiacal constellation of Cancer at this time of year — thus its name Cancer. The word “tropic” derives from the Greek word meaning turn — referring to the point on the sky where the sun changes direction and begins moving south as winter approaches in the northern hemisphere. Today, while precession (the wobble of the earth on its axis) has shifted the summer solstice into the constellational of Taurus, the solstitial sun remains in the astrological sign of Cancer, which is unaffected by precession. The Tropic of Cancer is currently at latitude 23 o 26.2’ N (23.44 o N). Like the obliquity, the latitude of the Tropic of Cancer varies from22.1 o Nand 24.5 o Nover about 41,000 years. The Tropic of Cancer is moving south toward the equator at about 50 feet per year.

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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. Tropic of Capricorn: This small circle (also called the Southern Tropic) forms the southernmost latitude on earth at which the noontime sun can cross the zenith. This occurs around Dec 21 — and is called the winter solstice in the northern hemisphere. A corresponding circle, also called the Tropic of Capricorn, is formed by the projection of the earth’s Tropic of Capricorn onto the celestial sphere. In ancient times, the sun passed through the zodiacal constellation of Capricornus at this time of year — thus its name Capricorn. The word “tropic” derives from the Greek word meaning turn — referring to the point on the sky where the sun changes direction and begins moving north as summer approaches in the northern hemisphere. Today, while precession (the wobble of the earth on its axis) has shifted the winter solstice into the constellational of Sagittarius, the solstitial sun remains in the astrological sign of Capricorn, which is unaffected by precession. The Tropic of Capricorn is currently at latitude 23 o 26.2’ S (23.44° S). Like the obliquity, the latitude of the Tropic of Capricorn varies from22.1 o S and 24.5 o Sover about 41,000 years. The Tropic of Capricorn is moving north toward the equator at about 50 feet per year. First ever Heritage Flame lit at Stoke Mandeville in a historic moment for Paralympic Movement". www.paralympic.org. 3 January 2014. Antarctic Circle: This small circle forms the southernmost latitude on earth at which the center of the sun’s disk travels completely around the horizon for a full 24 hours on the December solstice (summer solstice in the Southern hemisphere). Currently the latitude of the Antarctic Circleis 66 o 33.8’ S. The latitude of the Antarctic Circlevaries from67.9 o S and 65.5 o Sover about 41,000 years. The Antarctic Circleis moving north toward the equator at about 50 feet per year. Suspended within a ring, the sphere sits in a cradle 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.

The equinoctial A, which is divided into 360 degrees (beginning at its intersection with the ecliptic in Aries) 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 in which the sun is, on any given day, stands over that day in the circle of months. Darlington, Oscar G. "Gerbert, the Teacher," The American Historical Review (Volume 52, Number 3, 1947): 456–476. 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.De Rose, L.: La sfera armillare di Solunto, in XVIII Seminario di Archeoastronomia, 19–20 marzo, Sestri Ponente, Genova (2016) The instrument survived throughout the medieval period into the early modern era, and in many respects came to symbolise the queen of the sciences, astronomy. It wasn’t until the middle of the sixteenth-century that the basis of the instrument – a geocentric concept of the Universe – was seriously challenged by the Polish mathematician, Nicolaus Copernicus. Even then, the instrument still continued to serve a useful purpose as a purely mathematical instrument. The nomenclature of an armillary sphere is based on the terminology of the following astronomical coordinate systems (see table below). About it rotate a set of rings representing the heavens – the celestial sphere – with one complete revolution approximating 24 hours. It is believed that the Greek astronomer Hipparchus invented the armillary sphere around 200BC, to decipher how the heavens and stars moved around the earth. His sphere had a ball representing the earth in the centre, and four overlapping rings circling the globe.

Zenith: in the horizon coordinate system, it is the position directly overhead on the celestial sphere. The zenith’s altitude is 90 o. This particular instrument is Italian, made in Rome in 1588, and is signed by Carlo Plato. It has a number of unusual features that make it rather special, such as the moon mounted on a separate ring within the sphere, and a number of stars represented by individual pointers. 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.Aterini, B.: Geometric instruments for the orientation and measurement: the astrolabes. In: Advances in Historical Studies (AHS), 8, 58–78. Springer (2019b). http://www.scirp.org/journal/ahs. https://doi.org/10.4236/ahs.2019.81004 Over the centuries the design of the armillary sphere has been modified to coincide with new astronomical discoveries. Before the advent of telescopes in Europe in the seventeenth century, the armillary sphere was the primary instrument of all astronomers for determining celestial positions.