Among living things, the color blue is oddly rare. Blue rocks, blue sky, blue water, sure. But blue animals? They are few and far between. In this video, we'll look at some very cool butterflies with Bob Robbins, Ph.D. from Smithsonian's National Museum of Natural History to help us learn how living things make blue, and why this beautiful hue is so rare in nature. | Be Smart • PBS

Why Is the Sky Blue? When we look at the sky on a clear day, we see it as blue. But why does this happen? The answer lies in the interaction of sunlight with Earth's atmosphere, known as Rayleigh scattering. Rayleigh Scattering: Visible Light Spectrum: Sunlight is made up of a spectrum of colors ranging from red to violet, each with different wavelengths. Interaction with Molecules: As sunlight passes through the atmosphere, molecules and atoms in the air scatter the light. Shorter wavelengths (