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Eccentricity

5 Jul 2015, 00:00 UTC
Eccentricity
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¡SkyCaramba! Weekly astronomy blog for the week ending July 11, 2015
Some objects orbit other objects in nearly perfect circles. Others orbit in distinct ovals or ellipses. And others turn near another object, veer away, and never return. There’s a way to mathematically represent these variations. It’s called eccentricity.
An orbit that’s a perfect circle has no eccentricity at all. So, its eccentricity is said to be 0. Many satellites orbiting Earth are required to be in the same place in the sky at all times. They are put in orbits with eccentricities of 0.
If the orbit is just a little elliptical, its eccentricity must be a little more than 0. Venus has an eccentricity of 0.0068. It’s 109 million kilometers from the sun at aphelion and 107 million kilometers away at perihelion. It’s the most circular of the planets’ orbits in our solar system.
Earth’s orbital eccentricity is 0.0167. At aphelion in early July, our planet is 152.1 million kilometers from the sun. At perihelion in early January, the distance has shrunk to 147 million kilometers.
Mercury’s orbit is much more elliptical with an eccentricity 0.2056. The planet’s distance from the sun ranges from 69.9 million kilometers at ...

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