I use the sun as my primary lighting source for 99.9% of my photography. Todays news on CNN reported that Monday, Feb. 2 is Ground Hog Day here in the States and the length of the shadow cast by a certain groundhog in the state of Pennsylvania will determine the length of winter. The longer the shadow, the longer the winter. Now that seemed logical to me but my wife jumped all over that idea, arguing that the length of shadow is constant (at the same hour of the same day every year) regardless of luminous, a bright, clear day will produce the same length of shadow as a gray overcast day. Now I'm confused. What do you think? Is shadow length proportionate to light intensity?