The only planets known before the invention of the telescope were Mercury, Venus, Mars, Jupiter and Saturn. For centuries scholars thought that the Solar System consisted of just these five planets plus the Earth, the Sun and the Moon. Then, in 1781, the academic world received a rude shock when an amateur astronomer discovered another planet with his home-made reflecting telescope!
KeywordsSolar System Rotation Period South Pole Hubble Space Telescope Twilight Zone
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