A glass of water is transparent, so why is an entire sea blue?
Many people say it’s because the sea reflects the sky. But the sea stays blue on cloudy days, and so does the water in a huge aquarium tank—so reflection alone doesn’t quite explain it.
The real reason is mainly the water molecules themselves: water absorbs red and orange light especially strongly. As sunlight penetrates the sea, most of the red light is absorbed within a few meters. The remaining blue light is scattered in every direction by water molecules, and when it reaches your eyes, you see that blue.
That’s why the deeper the water, the bluer it looks. In shallow areas where you can see the bottom, it tends to look green or turquoise. Incidentally, a whole bottle of pure water actually looks faintly blue too—you just need several meters of it for the color to show. So why are some seas green? That’s mostly thanks to phytoplankton and sediment, as in the Yellow Sea.
When you take photos, do you prefer blue seas or green seas?
Many people say it’s because the sea reflects the sky. But the sea stays blue on cloudy days, and so does the water in a huge aquarium tank—so reflection alone doesn’t quite explain it.
The real reason is mainly the water molecules themselves: water absorbs red and orange light especially strongly. As sunlight penetrates the sea, most of the red light is absorbed within a few meters. The remaining blue light is scattered in every direction by water molecules, and when it reaches your eyes, you see that blue.
That’s why the deeper the water, the bluer it looks. In shallow areas where you can see the bottom, it tends to look green or turquoise. Incidentally, a whole bottle of pure water actually looks faintly blue too—you just need several meters of it for the color to show. So why are some seas green? That’s mostly thanks to phytoplankton and sediment, as in the Yellow Sea.
When you take photos, do you prefer blue seas or green seas?