Earth’s Speed

The time interval required for Earth to travel from the autumnal equinox to the vernal equinox (approximately 179 days) is less than the time interval from the vernal t the autumnal equinox (roughly 186 days). Why?

Answer

Since perihelion occurs in early January, Kepler’s second law implies that Earth is traveling faster during the winter months. The time for Earth to travel from the autumnal to the vernal equinox, taken as a fraction of the year (T = 178.83/365.25), can be used to find an accurate value of the eccentricity of Earth’s orbit, ε = 0.5 π (0.5 – T) = 0.01632, about 2 percent away from the precise value of    ε = 0.016713. A more accurate formula based on T is found in the reference below.