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Armillary Sphere

Armillary sphere with astrononomical clock Credit: Chris Bainbridge

Armillary sphere with astrononomical clock Credit: Chris Bainbridge

Despite the fact that the term “armillary sphere” sounds like a high-tech weapon or something from a science fiction movie, it is neither. An armillary sphere is an old tool that is supposed to represent the heavens. They were models of what scientists thought the heavens looked like and how they were suppose to have moved. The armillary sphere is also known as the spherical astrolabe, the armilla, or the armil. The armillary sphere is related to the astrolabe, which was a navigation tool used for determining the position of the Sun and stars and used by sailors for navigating.

The armillary sphere was invented hundreds of years ago. The identity of who created the sphere has been debated. Some credit its invention to a Greek named Eratosthenos. Others have said that the Chinese or other Greek scholars invented it. Regardless of its inventor, the armillary sphere is one of the oldest astronomical instruments in the world. In addition to its being used in the Greek world, the armillary sphere was also used throughout Asia and the Islamic Empire.

These devices were used as teaching tools and models. The models were used to show the difference between the Ptolemaic and Copernican theories of the Solar System. In the Copernican theory, the Sun is the center of our Solar System, while the Earth is the center of the Solar System according to the Ptolemaic theory. When armillary spheres were first invented, the Ptolemaic theory was still the accepted view. It was soon after armillary spheres were invented that Copernicus set forth his theory of the Sun as the center of the Solar System, although it was not widely accepted until centuries later.

The armillary sphere looks like a sphere circled by a ring and set upon a base. Armillary spheres were made with different numbers of circles arranged at various angles. Spheres with both four and nine circles have been known to exist – as well as ones with different numbers. These rings would then be adjusted in order to trace the path of the stars.

The armillary sphere also turns up in the Portugal flag, originally as a symbol for the country’s colony Brazil. The armillary sphere was widely used for navigating at sea, and exploration was heavily promoted by the Portugese royalty. In the early 1800’s, the sign was removed from the national flag when Brazil gained its independence. However, it was replaced in 1911 after Portugal became a Republic. You can still purchase armillary spheres today, although some of them are extremely expensive, especially if they are antiques.

Universe Today has articles on Solar System projects  and parallax.

If you are looking for further information, check out how to build an armillary sphere and astrolabes.

Astronomy Cast has an episode on telescopes.

Source: Wikipedia

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