Season of Truth

What determines the true start of a season, is it actually the date and time set by man, or is it the first sign of new growth in spring, a new bud or green breaking open the ground beneath my feet, could it be the first turn of yellow, red or orange of a leaf, or is it when all the leaves start to fall to the ground at my feet, is it the first frost, or the first dusting of snow? When does a new season truely begin, is it the date man as set or when nature itself is telling us so? ~Flassie