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| | Comets |
 | | Tycho deduced that the comet was at least four times farther away than the Moon, establishing for the first time that comets were heavenly bodies. |
 | | It was the English physicist and mathematician Isaac Newton who demonstrated in his Principia (1687) that, if heavenly bodies are attracted by a central body (the Sun) in proportion to the inverse square of its distance, they must move along a conic section (circle, ellipse, parabola, or hyperbola) |
 | | Observed on Christmas night, 1758, by Johann Georg Palitzsch, a German amateur astronomer, the comet passed at perihelion in March 1759 and at perigee (closest to the Earth) in April 1759. |
| www.geocities.com /zlipanov/comets/comets.html (10543 words) |
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