Why the Sky Is Blue

White light arriving from the sun, blue light taking detours off air molecules into your eye, the sun at the horizon skimming a long, grazing path through the air, and two side puzzles about clouds and Mars.

Before you start. You need to know that sunlight looks white but is secretly every color mixed together, the way a prism splits it into a rainbow. Nothing else - no formulas, just a lab, a sky, and a trick you can check with sunglasses in ten seconds.