## eccentricityr - _{a}r) / (_{p}r + _{a}r)
where _{p}r is the apoapsis distance and _{a}r is the periapsis distance. An almost circular orbit has an eccentricity close to zero. The
more elongated the orbit, the higher the eccentricity, up to a maximum value,
for a closed orbit, of 1. As a guide, the orbital eccentricity of most of
the planets in the Solar System is less than 0.1 (0.017 in the case of Earth),
although that of Mercury and Pluto exceeds 0.2. Eccentricity is one of the orbital
elements. _{p}## Related category• CELESTIAL MECHANICS | ||||||

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