Maths Museum Museum
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Armillary Sphere
© Museum of the History of Science, Oxford
Click Here for Interactive Exhibit This is an example of one of the most ancient types of mathematical instrument: an armillary sphere. An armillary sphere is basically a model of the universe.

This armillary sphere has a small brown-coloured ball at its centre. The ball is supposed to be the earth. It is surrounded by lots of metal rings. This is where the armillary sphere gets its name - 'armilla' in Latin means 'bracelet or arm ring'. The thickest metal ring, which has a slit down the middle, is supposed to show the path that the sun follows when it moves around the earth. The other rings represent the stars, or to be more accurate what used to be called the 'sphere of fixed stars' since ancient astronomers believed that the stars were fixed to the inside of a crystal sphere that went around the earth.

This armillary sphere was made over 500 years ago and is one of the oldest in the world. It shows the earth at the centre of the universe, with the sun and all the stars going round it. This is of course wrong. We now know that it is not the sun that goes round the earth but the earth that goes round the sun . However, when this armillary sphere was made people believed that the sun went round the earth. This was what the great astronomer Ptolemy had said in his famous work on astronomy called the Almagest. The Almagest was written in about AD 200. It was only in AD 1543 that the astronomer Nicolaus Copernicus proved that the earth went round the sun.

Although this armillary sphere is quite small (about 17 cm wide) it is coated with gold and is very valuable. It was probably made in Italy during the Renaissance. The Renaissance was a very important artistic and scientific period. A lot of progress took place in mathematics in the Renaissance. This armillary sphere may have been owned by a leading Renaissance scholar, or perhaps a prince, or an important clergyman like the head of a monastery. It would have been used for teaching school pupils about how the universe worked.

Even though this armillary sphere is small and would have been used for teaching, some armillary spheres were much bigger and were used to make measurements of the positions of stars. These bigger armillary spheres would have had metal plates attached to their rings, with holes in for astronomers to look through.

One famous astronomer who used armillary spheres to make measurements was Tycho Brahe. Tycho was Danish and was born in 1546. He had an observatory in a castle on a small island in the sea close to the capital of Denmark. In his observatory he had huge armillary spheres, several metres high. Tycho is famous for two funny reasons. Part of his nose was cut off in a fight and he had a silver fake nose made to replace it, which he sometimes took out and kept in his pocket. Also, he went to dinner once with an Emperor. At the dinner he needed to go to the toilet but was afraid to ask the Emperor if he could leave the table because it was rude to leave the table before the Emperor in those days. Unfortunately, he needed to go to the toilet so badly that his bladder burst. Worse still, this made him very ill and he died soon afterwards.

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