Observing the Vernal, Autumnal and Solstices was something done from ancient times, in ceremony and in ritual. Whole cities were built aligned to the cardinal directions of the compass and the lights of heaven. The lights of heaven were given to us first as "signs" and secondly as "seasons."
Don't let them pass by unnoticed. Otherwise you note less than even the plants and the animals whose life cycles and behavior acknowledge the passing of such events.