Since the dawn of humanity, we have tried to answer questions about how the universe works, from the simplest to the most complex natural events.
We are able to answer many questions, but at the same time, basic information ends up being lost to make way for deeper and more advanced questions.
That’s why questions like “Why is the sea blue?” still arise. It seems like a simple question, but have you ever stopped to think that water is colorless? So how is the sea blue if its water is transparent?
Physics can answer that question! In fact, renowned physicist Isaac Newton helped answer that question centuries ago.
Why is the sea blue?
Many people may think that this is the natural color of ocean water, or that it is the reflection of the sky in the water. But both are completely wrong. In fact, the reason why the color of seawater, rivers and lakes is generally blue is due to a basic phenomenon explained by physics called “refraction or dispersion of light”.
To understand, it is first necessary to know what this dispersion is. Well, the Sun sends different energies to Earth, that is, different types of light, and the only ones perceived by the human eye are the colors contained in the visible spectrum of light.
How does this happen at sea?
Sunlight is actually white, which is a polychromatic energy, that is, it is made up of all colors. And when it interacts with any medium, its path, speed and wavelength (which distinguishes colors) can change. In addition, it is absorbed or reflected.
Thus, ocean water, when it is not completely dirty or has several other particles, acts as a filter and absorbs almost the entire spectrum of light, except for blue or violet, which correspond to longer wavelengths and are more difficult to absorb.
However, this only occurs closer to the surface, because in deeper environments, all light is absorbed. Therefore, the seabed is completely dark.
But isn’t the water transparent?
Actually yes, but it depends on the amount of water we are referring to. For example, a glass of water does not have enough water to refract and disperse light significantly, so it simply passes through without much effort.
However, with huge masses of this liquid, as occurs in the seas, the dispersion becomes more effective. Thus, we can see that the quantity must really be high, since neither the pools are blue, nor even the shallowest part of the sea, close to the sand.
Additionally, there may be other colors in the oceans, depending on their composition and which light waves are reflected.
