How Copernicus watched the sky

How

COPERNICUS

watched the sky

by Polish team

The book was prepared as part
of the Erasmus+ project
2020-1-PL01-KA229-082143

The Times

The Middle Ages are generally known as the times when astronomy was not being developed to the heavy impact of Christianity over all aspects of scientific life. Therefore, geocetric model of the universe was widely established with the Earth as the centre of all the world.

That theory was developed by Claudius Ptolemy of Alexandria (2nd century BC). In his astronomical work entitled Almagest he presented a complete system of geometrical models, made of circles, large deferents and smaller epicycles that carry the planets. Meanwhile, the physical model of the universe was explained by Ptolemy in his Planetary Hypotheses. In the model described there, each planet moved in a spherical shell, which was thick enough to contain an epicycle, while the lower border of the shell of a planet situated closer to the outside was at the same the upper border of the shell of a planet closer to Earth.

Thanks to Ptolemy a long lasting order of planets became established, which was in increasing distance from the Earth: the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn.

However, in order to preserve the accuracy of prediction of planetary motions in his system, Ptolemy introduced some new solutions: the centre of an epicycle moved on the deferent at a constant speed, with respect not to its centre, but to an equant - a point situated as the mirror image of the Earth, on the opposite side of the centre of the deferent and at an equal distance from it. It was a significant departure from the Aristotles theory of motion in the ethereal world.

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Heliocentric system

Copernicus created a heliocentric model in which planets have the Sun as the fixed point to which their motions are to be referred; that Earth is a planet which, besides orbiting the Sun annually, also turns once daily on its own axis; and that very slow long-term changes in the direction of this axis account for the precession of the equinoxes.

This representation of the heavens is usually called the heliocentric, or “Sun-centred,” system—derived from the Greek helios, meaning “Sun.”

THE DIFFERENCE BETWEEN GEOCENTRIC AND HELIOCENTRIC SYSTEMS

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