Like many people of his time Nicole Oresme (c.1320/5-1382), a prominent philosopher of the late Middle Ages, observed that just as sailors on passing ships find it difficult to identify which of the ships is moving, so Earth rotating under a stationary Sun would give the same appearance as the Sun orbiting a stationary Earth. He also noted how much simpler things would be if the former were true rather than the latter.
The whole Universe is in motion: the galaxies are receding from each other; the stars, including our star, the Sun, orbit the centre of the Galaxy (ours); Earth orbits the Sun; the Moon orbits Earth; and Earth rotates on its axis. With respect to Earth, however, the Sun (due to its relative position to Earth) and the stars (because of their distance from Earth) can be regarded as being (almost) fixed in space.
In the northern hemisphere to see the Sun we look southwards and east is to our left. It is Earth rotating anticlockwise(eastwards) that makes the Sun appear to be moving left to right westwards (clockwise) across the face of the planet.
Earth spins at 360/24=15°/hour, which makes the Sun appear to be moving westwards at approximately one angular diameter every two minutes (60×0.5/15) – the Sun and Moon each have an angular diameter of approximately half a degree.
Earth’s axis points northwards to a position close to Polaris, the North Star or Pole Star, which seems to remain almost motionless while the other stars rotate anticlockwise around it ‘above’ Polaris other stars appear to be moving westwards, and ‘below’ Polaris they seem to be moving eastwards) and complete one revolution in about twenty-four hours. But at this distance the movement of the stars is almost undetectable; it is Earth’s own anticlockwise rotation that gives the appearance of the other stars rotating around Polaris.
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