The planet
orbits faster when it is
closest to the sun. So perihelion is the point in the
orbit when the planet is
traveling the fastest. This is
why our calendar months
have irregular
lengths.
Pope Gregory
XIII hired some astronomers to
create the Gregorian
calendar (1582) to guarantee the
solstices and equinoxes would
always fall on the 21st of
Dec, Mar, Jun, and Sep.