What makes our oceans blue? - The physical explanation of why we can call our Earth the "Blue Planet".

Whether it's red lips, a yellow vest, or a blue eye – most of the colors we see every day are determined by the reflection, scattering, and absorption of light. At first glance, the principle seems reversed: we see blue ink as blue precisely because the ink absorbs other colors like yellow, green, and red and reflects blue light. It's similar with the ocean. Blue light is absorbed the least by water. This allows it to penetrate deeper waters, down to almost 100 meters. The light is scattered by sediments and microorganisms in the water. With increasing depth, this scattering is primarily blue light. That's why we see bodies of water as blue, and deeper waters as bluer.

"You often hear that the blue ocean simply reflects the blue sky. But that's not true. Both are blue independently of each other. In both cases, the explanation has to do with light scattering, that is, the deflection of light rays in different directions when they hit particles," Nathalie Agudelo points out, highlighting a widespread misconception. The doctoral candidate works in the Danzl research group at the Institute of Science and Technology Austria (ISTA) on novel microscopes to better observe biological processes. "Atmospheric molecules scatter blue light more strongly than red light because blue light has a higher frequency. So, when we look at any point in the sky, the blue light that reaches us is scattered in our direction. We are all familiar with the colorful spectacle of a sunset when the sun is low on the horizon. In this case, the sunlight has to travel a long distance through the atmosphere, so the blue components are scattered out, and we mainly see the orange-red, unscattered light."