The sky is blue. The ocean is, too. But the reasons why are very different.

If you’ve ever been curious about the world you live in, you’ve probably wondered why the sky is blue. It’s a question that most children ask at some point in their lives, but the answers that adults give them often don’t align with our physical reality. Some of the more common incorrect answers that people often give in response include: While none of those answers are correct, that last attempt brings up a related question that people often wonder about: why are the oceans blue?

As seen from space, planet Earth is often described as a pale blue dot, but it’s only the liquid bodies of water ⁠— dominated by Earth’s oceans ⁠— that appear blue-hued. The continents, clouds, and ice caps don’t appear blue at all. That allows us to conclude that it’s the oceans, rather than the atmosphere, that give our planet its overall blue complexion.

For thousands of years, humanity had to simply accept these properties of our world as observed facts: we knew them to be true, but didn’t understand the physical cause behind them. With the advances of modern science, however, we now fully understand why both the skies and oceans are blue. Regardless of where the Sun is in the sky, the color of the sky toward the zenith (directly overhead) is a much darker blue, while the sky toward the horizon is a lighter, brighter cyan color.

This is due to the larger amount of atmosphere, and the larger amount of scattered light, that is visible at low angles in the sky. Contrary to what you might have read, there’s no one single factor responsible for Earth’s blue skies. The skies aren’t blue because sunlight has a blue tint; our Sun emits light of many different wavelengths, and that light sums up to be a net white color.

Oxygen itself isn’t a blue-colored gas, but rather is transparent to light: relatively equally across all of the visible wavelengths. Get the fall print issue, shipping in October, to members only. However, our atmosphere is made up of much more than the nitrogen and oxygen that composes 99%, by mass, of the gaseous-phase matter that surrounds our world.

There are a myriad of molecules and larger particles in our atmosphere that play a major role in terms of physics, scattering light of different wavelengths by different amounts. The ocean plays no role in the color of the skies, but the sensitivity of our eyes absolutely does matter: we do not see reality as it is, but rather as our senses perceive it and our brain interprets it. Through the vacuum of space, all light, regardless of wavelength or energy, travels at the same speed: the speed of light in a vacuum.