... epicycle, the centre of which – the deferent – itself moved round the Earth in a perfect circle ᭤ The Copernican theory – placing the Sun in the centre removed many of the difficulties of the Ptolemaic... and used them to make spectacular discoveries; he saw the mountains and craters of the Moon, the phases of Venus, the satellites of Jupiter, spots on the Sun and the countless stars of the Milky... have been erected One of the most recent, Gemini North, is seen in the foreground The main advantage of the site is the thinness of the atmosphere, and the fact that most of the atmospheric water