Counterintuitively clouds are heavy, in a way, because they're so large. The Sun is another interesting (size * density) example. The Sun's "power per unit vol

Counterintuitively clouds are heavy, in a way, because they're so large. The Sun is another interesting (size * density) example. The Sun's "power per unit volume" is only about the same as a compost pile. But because it's so large, this is enough to keep it glowing brightly.