History of Armillary Sphere Sundials
Around 225BC an Egyptian astronomer and mathematician, Eratosthenes of Cyene devised an instrument called an armillary to represent the ancient Greek concept of the universe. The armillary sphere instrument consisted of a series of metal rings, similar to the hoops of a barrel, joined together in the form of a hollow sphere with a small globe representing the Earth at the centre of the sphere. The instrument showed the heavens encircling the Earth, and the signs of the zodiac were frequently engraved or cast into one of the metal rings. At a later date it was used by astronomers for observational purposes connected with the mathematics of spheres. The assembly of rings was called an armillary after the Latin word ‘armilla’, meaning a bracelet or ring. Originally ten rings were used and they denoted the ten major circles of the celestial and terrestrial spheres placed in the correct relationship to one another.
Parts of an armillary sphere sundial
An ancient armillary
A modern sundial of this type is generally made up from a series of just three metal rings, joined together to form a hollow sphere with a thin metal rod passing through the centre which acts as the gnomon to cast the time-telling shadow onto an hour scale inside the equatorial ring. The angle of the gnomon rod is determined by your latitude.
The armillary sphere instrument was not used as a sundial until about the 17th century when it was referred to as 'an instrument for laying out or calculating sundials'. Soon afterwards, the armillary sphere began to be used itself as an accurate time-telling device and it became known as the armillary sphere sundial, which is its name to this day. Ten rings are now rarely used because of the confusion which arises from the many shadows and the consequently reduced number of hours for which the sundial can be used successfully.
Each ring represents one of the following:
1. the Celestial Equator (the Equatorial ring, which contains the hour scale)
2. the Meridian circle which lies in the true North-South plane
3. the Horizontal Plane (the Plane of the Ecliptic) or sometimes the Polar Plane which is perpendicular to the Equatorial plane.
The rings are sometimes decorated with poetry, picture stories, signs of the zodiac, family coats of arms and similar.
Our smaller basic design Model AS1 is shown here while the larger Model AS2 is shown below.
Schematic of Model AS2 with suggested approximate size for pedestal
A bronze commemorative / dedication plaque is provided with words and ornamentation of your choosing. This plaque incorporates the Time Correction graph which links Solar Time and your Zone Standard Time. The plaque can be any shape and size you desire and can be installed either on your pedestal or on a separate plinth nearby. Alternatively, on Model AS1 it can be incorporated into a slightly larger sundial baseplate.
Specifications for Models AS1 and AS2:
Armillary sphere sundial with three intersecting rings (meridian, polar and equatorial rings), cast in gunmetal bronze LG2 alloy, each ring having rectangular cross section. Each of the thirty or so joints are deep penetration welded, annealed and smoothly finished to give high strength and tactility. The sundial has graceful, functional design whilst simultaneously exhibiting high vandal resistance based upon our almost 40 years of sundial design experience.
We have 2 similar models which vary in size. The larger sphere, Model AS2, has Internal diameter for the time scale and rings of 500 mm, outside diameter of rings approximately 600 mm, and overall height about 800 mm above the pedestal. This assembly weighs about 80 kg. The smaller sphere, Model AS1, has internal diameter for the time scale and rings of 350 mm, outside diameter of rings approximately 410 mm, overall height about 510 mm above the pedestal and weighs about 30 kg. You supply your own pedestal as everyone has such different preferences.
This superb armillary sphere at Port Elliot is made from stainless steel with spherical surfaces for each of the 3 rings. It is 1200mm in diameter. The rings were cut flat from 12mm thick material using a high pressure jet of water and the hour numbers and markings on the hour scale were machined in the same way.
The flat rings were rolled with specially shaped rollers then welded together and ground smooth. This sundial stands on a large basalt slab in a private native plant garden, overlooking the southern coastline of South Australia.
The grand armillary sphere sundial in the Herb Garden of the Royal Botanic Garden Sydney was a gift to the Garden and the people of Sydney from the Arnott family. The sundial body with its internal spherical surfaces was cast in silicon bronze in 11 pieces using traditional sand casting techniques then welded together. It stands about 2.5 metres tall and weighs 1.5 tonnes. The horizon ring is richly decorated with 38 well-known herbs, slightly larger than life size, together with the famous symbolic Arnott parrot. The herbs were cast in high relief in silicon bronze, using a modern variant of the ancient 'lost wax' process.
Please Contact us to discuss your own personalised armillary sphere sundial. The cost of your commission depends on your specific requirements. The prices for Models AS1 and AS2 are shown on the Prices page.