I had one of those "Why didn't that ever occur to me before?" moments. The time between the #Equinoxes is not symmetrical. It's about 186 days between the #March and #September equinoxes and about 179 days from September to March. This is because the speed of the #Earth in its #orbit varies as it's #elliptical rather than circular. I never bothered to count the days and yet it's "obvious" when you look at the calendar. This gives an eccentricity of the orbit to be around 0.015 which is remarkably close to the actual value.
https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion