Earth and Space

Greek evidence for the Earth's shape and spin

Teaching Guidance for 14-16 PRACTICAL PHYISCS

A round Earth

Pythagoras' pupils, if not the great man himself, knew that the Earth is round. Traveller's tales of ships disappearing over the horizon and noticing bright stars, such as Polaris, shifting to a higher position in the sky as one journeyed north suggested a curved Earth.

Aristotle (about 340 BC), two centuries later, supported the idea of a spherical Earth, Moon and planets because:

  • the sphere is a perfect solid and the heavens are a region of perfection
  • the Earth's component pieces, falling naturally towards the centre, would press into a round form
  • in an eclipse of the Moon, the Earth's shadow is always circular: a flat disc would cast an oval shadow
  • even in short travels northwards certain stars, such as Polaris, appear higher in the sky.

This mixture of dogmatic reasons and experimental common sense was typical of him and he did much to set science on its feet.

A spinning Earth

is a type of Planet
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