Practical activities designed for use in the classroom with 11- to 19-year-olds.
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# Pythagorean model of the Universe

#### Demonstration

An umbrella model of the Pythagorean system.

#### Apparatus and materials

Umbrellas, 2, black expandable

#### Health & Safety and Technical notes

Make sure no ribs of the umbrella are exposed at their edges.

Cut the spike off the inner umbrella and cut a hole in its fabric for the handle of the outer umbrella, such that the two can be inclined at 23 1/2° to each other. Mark the star pattern on the inner umbrella and a planet or the Sun on the outer one. This can be represented by a polystyrene sphere fixed to one of the spokes at the rim.

#### Procedure

Spin the inner umbrella, carrying the outer one with it, one rotation representing one day. Adding a slow rotation of the outer umbrella from west to east shows the planet's yearly movement backwards round the ecliptic.

#### Teaching notes

1 See the guidance note Early astronomical observations.

2 Pythagoras (about 530 BC) developed a more complex model then Thales' model. The Pythagorian School accepted that the Earth was a sphere. The stars and planets were imagined to sit on an imagined scheme of concentric spheres, like shells of an onion: the 'Crystal Spheres'. The outermost sphere carried the stars with the daily motion. Inside were other spheres, each carrying a planet. Starting from the outermost, they were in this order:

Stars
Saturn
Jupiter
Mars
Sun
Mercury
Venus
Moon

In later stages, this model of celestial spheres had all the spheres attached to the outermost one, which carried them round with the 24-hour motion. Then the Sun's sphere revolved backwards once a year about an axis on the ecliptic. The spheres for the Moon and other planets all revolved slowly backwards about the same axis; one revolution a month for the Moon; one revolution in 12 years for Jupiter.

This model imitated the motion of the Sun and Moon fairly well but gave only the general motions of the planets without their retrograde loops.

This experiment was safety-checked in April 2007

#### Related guidance

Page last updated on 08 November 2011