# How is eccentricity calculated with perihelion and aphelion?

Orbit is elliptic. Parameters. a = semi-major axis and e = eccentricity. Aphelion = a(1 + e); perihelion = a(1 - e). The sum gives major axis 2a and the difference is 2ae. So, e = sum/difference.

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The following formula is used to calculate eccentricity: [ e = \frac{r_a - r_p}{r_a + r_p} ] Where: - ( e ) is the eccentricity; - ( r_a ) is the distance between the ellipse's center and the aphelion; - ( r_p ) is the distance between the ellipse's center and the perihelion

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