The Earth and Time
The ancients considered the Earth to be flat and located at the centre of the Universe, with the sky a crystal dome on which the stars were fixed. Around 2 000 bc Aristotle realised that the Earth is a globe. There is clear evidence to support this view. For instance, there is the differing altitude of the pole star as seen from different locations and the fact that the most southerly of the constellations are only rendered visible by travelling southwards (the converse is true for people living in the southern hemisphere). More commonly known is the phenomenon of a ship travelling away from the shore disappearing from view whilst its sails are still visible above the horizon. The sails are then seen to ‘sink’ below the horizon as the ship further recedes.
KeywordsCelestial Body Solar Time Sidereal Time Vernal Equinox Celestial Pole
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