Free Orbital Eccentricity Calculator
Compute the eccentricity of an orbit from its periapsis and apoapsis distances: e = (r_a - r_p) / (r_a + r_p).
km
km
Eccentricity
0.016711
Semi-Major Axis149,600,000 km
Eccentricity vs Periapsis Distance
Orbital Eccentricity
Eccentricity describes how elongated an orbit is (0 = circle, approaching 1 = very elongated ellipse).
Formula
e = (r_a - r_p) / (r_a + r_p)
Semi-major axis: a = (r_a + r_p) / 2
Example Calculation
Earth: perihelion 147.1M km, aphelion 152.1M km.
- 01e = (152.1M - 147.1M) / (152.1M + 147.1M)
- 02e = 5M / 299.2M ≈ 0.01672
- 03a = 299.2M / 2 = 149.6M km