Mars is the most prominent planet in the evening sky right now. To find The Red Planet, look to the southern horizon just after dark. Mars is bright rusty orange in color and will shine with a steady light while stars will twinkle. This summer we had a favorable opposition with Mars at. The next opposition will occur in October of when Mars will be.
Whether it is the polar ice caps of Mars, rings of Saturn, the stormy clouds and dancing moons of Jupiter, or the dramatic, Moon-like phases of Venus, the Wanderers will entice the backyard astronomer to explore the night sky.
It was the standard astronomical reference until the Renaissance. In the theory of Ptolemy, the planets moved in small orbits while revolving in large orbits about the Earth. This theory, although incorrect, could explain the apparent motions of the planets and also account for changes in their brightness.
The Greeks "What are the uniform and ordered movements, by the assumption of which the apparent movements of the planets can be accounted for? Basically, if we didn't have planets, we couldn't live. But Earth is a planet. By Leah Crane.
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It can be seen that the Moon and the Sun do not possess epicyles. Moreover, the motions of the inferior planets i.
In fact, the centres of the inferior planet epicycles move on an imaginary line connecting the Earth and the Sun. Furthermore, the radius vectors connecting the superior planets i. Note that, in addition to the motion indicated in the diagram, all of the heavenly bodies including the stars rotate clockwise assuming that we are looking down on the Earth's North pole in Fig.
Finally, there are epicycles within the epicycles shown in the diagram. In fact, some planets need as many as 28 epicycles to account for all the details of their motion. These subsidiary epicycles are not shown in the diagram, for the sake of clarity. As is quite apparent, the Ptolemaic model of the Solar System is extremely complicated. However, it successfully accounted for the relatively crude naked eye observations made by the ancient Greeks. The Sun-linked epicyles of the inferior planets are needed to explain why these objects always remain close to the Sun in the sky.
The epicycles of the superior planets are needed to account for their occasional bouts of retrograde motion : i. Finally, the displacement of the Earth from the centre of the deferants, as well as the introduction of the equant as the centre of uniform rotation, is needed to explain why the planets speed up slightly when they are close to the Earth and, hence, appear brighter in the night sky , and slow down when they are further away.
Figure The Ptolemaic model of the Solar System. Ptolemy's model of the Solar System was rescued from the wreck of ancient European civilization by the Roman Catholic Church, which, unfortunately, converted it into a minor article of faith, on the basis of a few references in the Bible which seemed to imply that the Earth is stationary and the Sun is moving e.
Consequently, this model was not subject to proper scientific criticism for over a millennium. Having said this, few medieval or renaissance philosophers were entirely satisfied with Ptolemy's model. Their dissatisfaction focused, not on the many epicycles which to the modern eye seem rather absurd , but on the displacement of the Earth from the centre of the deferants, and the introduction of the equant as the centre of uniform rotation.
Recall, that the only reason planetary orbits are constructed from circles in Ptolemy's model is to preserve the assumed ideal symmetry of the heavens. Unfortunately, this symmetry is severely compromised when the Earth is displaced from the apparent centre of the Universe.
This problem so perplexed the Polish priest-astronomer Nicolaus Copernicus that he eventually decided to reject the geocentric model, and revive the heliocentric model of Aristarchus. After many years of mathematical calculations, Copernicus published a book entitled De revolutionibus orbium coelestium On the revolutions of the celestial spheres in which outlined his new heliocentric theory.
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