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. De Rose, L.: La sfera armillare di Solunto, in XVIII Seminario di Archeoastronomia, 19–20 marzo, Sestri Ponente, Genova (2016) Aterini, B.: The astrolabe: a mechanism for reading the stars. In: Zhang, B., Ceccarelli, M. (eds.) Explorations in the History and Heritage of Machines and Mechanisms. HMMS, vol. 37, pp. 227–242. Springer, Cham (2019a). https://doi.org/10.1007/978-3-030-03538-9_19 Christopher Cullen, "Joseph Needham on Chinese Astronomy", Past and Present, No. 87 (May, 1980), pp. 39–53 (45) 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.

An armillary sphere can be turned into an armillary sundial by setting its celestial polar axis equal to the latitude of the sundial’s location and directed at the North Celestial Pole. The sphere’s Horizon ring is fixed parallel to the terrestrial horizon. And finally the meridian ring called the Solstitial Colure, which passes through the celestial poles and the two solstices, is rotated to the vertical position so as to coincide with the local meridian of the sundial’s location. Terminology of astronomical coordinate systems 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 Symonds papers are held by Winterthur Museum in the USA. With the Symonds papers is an album of photographs labelled ‘Furniture Sandridgebury No 1’. Symonds wrote a ‘Portrait of a Collector’ about Percival Griffiths, in Country Life, June 13, 1952. R W Symonds’ book ‘English Furniture from Charles II to George II’ (1929) is illustrated with items from the Sandridgebury collection. In the foreword Griffiths writes of his experience and philosophy as a collector. See also 'Intuitively Collected', by Simon Houfe, Country Life 27 December 1990. 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. 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]

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.

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

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. 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. 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.