After reading about the precession of the equinoxes and the change of the seasons over thousands of years, I was wondering if the equinoxes and solstice dates are actually getting earlier or later to compensate for this phenomena?  I've always known them to be on the 21st December and 21st June (with a bit of fluctuation), I also know the Gregorian calendar changed from the Julian calendar, was this because of this phenomena, please help.