Elliptical Orbit - Encyclopedia Britannica

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comets

• In comet: Ancient Greece to the 19th century

  …Any less-eccentric orbits are closed ellipses, which means a comet would return.

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• In comet: Ancient Greece to the 19th century

  …orbit was indeed a closed ellipse. Moreover, he showed that the orbital period of the comet around the Sun was only 3.3 years, still the shortest orbital period of any comet on record. Encke also showed that the same comet had been observed by French astronomer Pierre Méchain in 1786,…

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• In comet: Ancient Greece to the 19th century

  …that most comets were on elliptical orbits and thus were members of the solar system. Many were recognized to be periodic. But some orbit solutions for long-period comets suggested that they were slightly hyperbolic, suggesting that they came from interstellar space. That problem would not be solved until the 20th…

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• In comet: The modern era

  …the apparently hyperbolic orbits became elliptical. That proved that the comets were members of the solar system. Orbits of that type are referred to as “original” orbits, whereas the orbit of a comet as it passes through the planetary region is called the “osculating” (or “instantaneous”) orbit, and the orbit…

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• In comet: The modern era

  …sufficient to change the previously elliptical orbits of the comets to hyperbolic, ejecting them from the solar system and sending them into interstellar space. Van Woerkom also showed that because of Jupiter, repeated passages of comets through the solar system would lead to a uniform distribution in orbital energy for…

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• In comet: The modern era

  …often changed from hyperbolic to elliptical. Very few comets were left with hyperbolic original orbits, and all of those were only slightly hyperbolic. Marsden had provided further proof that all long-period comets were members of the solar system.

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Kepler’s laws

• In Kepler’s laws of planetary motion

  …move about the Sun in elliptical orbits, having the Sun as one of the foci. (2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time. (3) The squares of the sidereal periods (of revolution) of the planets are directly proportional to…

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• In celestial mechanics: Kepler’s laws of planetary motion

  An ellipse (Figure 1) is a plane curve defined such that the sum of the distances from any point G on the ellipse to two fixed points (S and S′ in Figure 1) is constant. The two points S and S′ are called foci, and the…

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planetary orbits

• In orbit

  …of another planet, elliptical; some elliptical orbits are very nearly circles, while others are much elongated. Some bodies may follow parabolic or hyperbolic paths (open-ended curves). The orbit of a body approaching the solar system from a very great distance, curving once around the Sun, and receding again is such…

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• In solar system: Orbits

  …move around the Sun in elliptical orbits in the same direction that the Sun rotates. This motion is termed prograde, or direct, motion. Looking down on the system from a vantage point above Earth’s North Pole, an observer would find that all these orbital motions are in a counterclockwise direction.…

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