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| the point of nearest approach of the planet to the Sun |
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| the point of greatest separation of the planet to the sun |
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| I. The orbits of the planets are ellipses, with the Sun at one focus of the ellipse. |
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| II. The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse. |
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| III. The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes: |
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| the part of the shadow where only a portion of the light source is obscured (seen in a partial eclipse) |
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| the darkest part of the shadow, where the light source is completely blocked by the occluding body. An observer in the umbra experiences a total eclipse |
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| the point farthest from a planet or a satellite (as the moon) reached by an object orbiting it |
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| the point nearest a planet or a satellite (as the moon) reached by an object orbiting it |
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Definition
| a change in the orientation of the rotation axis of a rotating body |
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