Armillary spheres (sometimes referred to as armillary sundials) are a common decorative ornament in many gardens but can most often be spotted in the traditional English garden. Today's armillary spheres, used as simply a decorative feature instead of a scientific instrument. are primarily fabricated of metal, and have become much more streamlined compared to their ancient counterparts.
So what exactly is an armillary sphere, you might wonder? The invention of the armillary sphere has been credited to everyone from a Roman mathematician to an ancient Greek philosopher to a Chinese astronomer. But while its origins may be debated, the one shared belief is that it was invented with the erroneous notion that the earth was the center of the universe.
Armillary spheres were developed as a scientific model which illustrated the workings of the celestial sphere, a concept that helped early astronomers and scientists to understand and explain the movements of the heavens. With the earth being viewed as the center of the universe, and the celestial sphere consisting of objects visible from earth, the armillary sphere calculated the position of something in the sky as it relates to an observer on earth.
Derived from the Latin word armilla — which can be defined as a bracelet or ring — the sphere indicates the heavens, while the intersecting rings marked everything from latitude and longitude to the Tropic of Cancer. As time and scientific knowledge progressed, so too did the instrument. Rings were added to mark the rotation of the sun, equator, moon and planets, which made these spheres some of the first complex mechanical devices. As the sun travels across the sky, the gnomon (or arrow) of the armillary sundial casts a shadow onto a surface that indicates the hour. And since they were used outside in view of the sky, they could often be found placed in a garden.