This Saturday is the Autumn Equinox, when the sun crosses the equator, causing day and night to be of equal length. This day marks the coming of winter, when days are shorter and nights are longer. The Equinox is a symbol of balance, but also one of change.
On a somewhat related note, I found this quote about change, which I like very much:
"All changes, even the most longed for, have their melancholy; for what we leave behind us is a part of ourselves; we must die to one life before we can enter another."
~ Anatole France