When you are on the beach, you can only pick up the sea water. It is no different from ordinary water. It is transparent and colorless. Then why does the sea look completely different from the transparent color? Today, I sorted out the color of the sea for you. Why is it not transparent but blue_ The reason why the sea is blue is for your reference. Let's have a look!
Why is the sea blue
In fact, this is the sun's magic. We know that sunlight is composed of seven colors: red, orange, yellow, green, green, blue and purple. When sunlight shines on the sea, red and orange light with longer wavelength can overcome obstacles and move forward bravely due to their maximum transmission force. As they move forward, they are constantly absorbed by seawater and organisms in the ocean. Blue light and purple light, due to their shorter wavelengths, scatter in all directions and even are reflected back when encountering the obstruction of sea water. Only a small part of them are absorbed by sea water and sea surface organisms.
The sea looks blue because this part of the scattered and reflected blue and purple light enters our eyes. The deeper the water, the more blue light is scattered and reflected, and the bluer it looks.
In fact, clean fresh water is also blue for the same reason as the above. Most of the water we usually see is green, mainly because the water body contains a lot of green algae. For example, in the Red Sea, there is a kind of algae growing in the water, which appears seasonally. After these algae die, they are reddish brown. Therefore, the Red Sea is also named, but the Red Sea is not red.
Why is the sea and sky blue?
The blue sky, the lighter light near the horizon, the redness of the sun at sunrise or sunset, and the blue of the ocean can be scientifically explained as an independent phenomenon.
If you've ever been curious about the world you live in, you may want to know why the sky is blue. The wrong answers people often answer include:
The sun is blue,
Oxygen itself is a blue gas,
Or the sky reflects the ocean.
Although these answers are not correct, the last attempt raises a related question that people often want to know: why is the ocean blue?
From space, planet earth is usually described as a light blue dot, but it just looks like a blue ocean. Continents, clouds and ice caps don't show blue at all; The ocean, not the atmosphere, brings blue "skin color" to our planet. For thousands of years, our world must accept these attributes. But with the progress of modern science, we understand why the sky and ocean are blue.
When the sun is high, the sky towards the zenith is a deeper blue, while the sky towards the horizon is a brighter, brighter cyan. This is due to the large amount of atmosphere and the large amount of scattered light visible at a low angle in the sky.
Contrary to what you may have read, there is no single factor that can explain the earth's blue sky. The sky is not blue, because the sun is blue; Our sun emits many different wavelengths of light, and the sum of light is net white. Oxygen itself is not a blue gas, but is transparent to light. However, countless molecules and larger particles do play a role in our atmosphere, scattering light of different wavelengths in different amounts. The ocean has no role in the color of the sky, but the sensitivity of our eyes is absolutely this: we will not see reality, but our senses will perceive it, and our brain will explain it.
These three factors - the light of the sun, the scattering effect of the earth's atmosphere, and the response of the human eye - are the blue appearance of the sky.
Schematic animation of a continuous beam scattered by a prism. If you have ultraviolet and infrared eyes, you will be able to see that ultraviolet light is more curved than violet / blue light, and infrared light is less curved than red light.
When we pass sunlight through a prism, we can see how it splits into components. The highest energy light is also the shortest wavelength (and high frequency) light, while the light with lower energy has a longer wavelength (and low frequency) than its high energy light. The reason for light splitting is that wavelength is the key attribute determining the interaction between light and matter.
The large hole in the microwave oven allows short wavelength visible light in and out, but keeps longer wavelength microwave light in and reflects it. The thin coating on sunglasses reflects ultraviolet, violet and blue light, but allows longer wavelengths of green, yellow, orange and red to pass through. The tiny invisible particles that make up our atmosphere - molecules such as nitrogen, oxygen, water, carbon dioxide and argon atoms - scatter light at all wavelengths, but preferentially at bluer, shorter wavelengths.
Rayleigh scattering affects blue light more seriously than red, but purple light is the most dispersed in the visible wavelength. Just because of the sensitivity of our eyes, the sky is blue instead of purple. The difference between the visible light with the longest wavelength and the visible light with the shortest wavelength experiencing Rayleigh scattering is almost an integer order of magnitude.
There is a physical reason behind this: all the molecules that make up our atmosphere are smaller than the various wavelengths of light that the human eye can see. Wavelengths closer to the existing molecular size will scatter more effectively; In quantity, it obeys a law called Rayleigh scattering.
Under the short wavelength limit we can see, the scattering frequency of purple light is 9 times higher than that of red long wave light at the other end of our vision. This is why during sunrise, sunset and lunar eclipse, red light can still pass through the atmosphere effectively, but more wavelength light is almost absent and is preferentially scattered.
Some milky white materials, as shown here, have similar Rayleigh scattering characteristics to the atmosphere. The white light from the top right shines on the stone. The stone itself scatters blue light, but allows orange / red light to preferentially pass through the unobstructed light.
Because the bluer wavelengths of light are easier to scatter, any direct sunlight entering will become redder and redder, and the atmosphere passing through it will become redder and redder. However, the rest of the sky will be illuminated by indirect sunlight: light hits the atmosphere and is redirected to your eyes. The wavelength of most light is blue, which is why the sky is blue during the day.
If there is enough atmosphere to scatter blue light into your eyes, it will only show a redder tone. If the sun is below the horizon, all light must pass through a large amount of atmosphere. Bluer light scatters in all directions, while redder light is less likely to scatter, which means it needs a more direct path to your eyes. If you have ever been on a plane after sunset or before sunrise, you can see the spectacular effect.
From the high-altitude areas of the sky before sunrise or after sunset, you can see a series of colors, which are caused by multiple sunlight scattering in the atmosphere. Direct light from near the horizon becomes extremely large, and indirect light is only blue when away from the sun.
This may explain why sunsets, sunrise and eclipses are red, but it may make you wonder why the sky is blue rather than purple. In fact, purple light actually comes from the atmosphere more than blue light, but there is also a mixture of other colors. Because your eyes have three types of cones (used to detect color) and monochrome bars, the brain needs to interpret all four signals when assigning color.
Each type of cone plus rod is sensitive to different wavelengths of light, but all of these cones are stimulated to some extent by the sky. Our eyes respond more strongly to blue, cyan and green wavelengths of light than to violets. Even if there is more purple light, it is not enough to overcome the strong blue signal provided by our brain, which is why the sky is blue in our eyes.
The first view of human eyes rising on the limbs of the moon. Discovering the earth from space with the human eye is still one of the most representative achievements in the history of our species. Apollo 8 took place in December 1968. It is one of the important precursor missions to successfully land on the moon. It will celebrate its 50th anniversary in July this year. Note that the earth's blue is due to the ocean, not the atmosphere.
On the other hand, the ocean is a completely different story. If you look at the whole planet and look at the planet you get from space, you will notice that the water bodies we have are not uniform blue, but based on their shadows. The depth of the water. Deep water is dark blue; Light water is light blue.
You will notice that if you look closely at the photos below, the waters bordering the continent (along the continental shelf) are shallower and greener blue than the dark deep sea.
The earth's oceans may appear blue, but along the continental shelf, they look lighter than the deepest blue of the ocean. This is not an artifact of the image construction method, but a real phenomenon. It describes in detail the differences of absorption and reflection of the ocean itself at different depths.
If you want more direct evidence that the ocean itself looks blue, you can try diving under the water and record what you see. When we do this, we take underwater photos in natural light - that is, there is no artificial light source - and we can immediately see that everything takes on a blue hue.
We go farther and farther. When we reach the depth of 30 meters, 100 meters and 200 meters, everything will appear blue. It makes sense to remember that water, like the atmosphere, is made of molecules of finite size: smaller wavelengths than any light we can see. But here, deep in the ocean, the physics of scattering is a little different.
If you fall into a water body and only allow the surrounding natural sunlight to shine on your environment, you will find that everything is blue, because red light is the first red light to fully absorb its wavelength.
When light passes through, the main function of the atmosphere is scattering, not scattering. Liquids such as water mainly absorb (or do not absorb) light. Like all molecules, water has priority over the wavelength it can absorb. Water not only has a direct wavelength dependence, but also absorbs infrared light, ultraviolet light and red visible light most easily.
This means that if you lower your head to a moderate depth, you will not be heated by the sun, you will be protected from ultraviolet radiation, and as the red light is taken away, things will begin to turn blue. Go down a little and the oranges will disappear.
At deeper depths, when the water is exposed to the natural sunlight from above, not only red, but also orange and yellow begin to disappear. Even the lower green is absorbed, leaving only a faint blue light.
In the past, yellow, green and violet began to be taken away. When we go to a depth of more than kilometers, the blue light will disappear at last, although this is the last time.
This is why the deepest ocean depths appear dark blue: because all other wavelengths are absorbed. The darkest blue is unique in all wavelengths of light in the water, with the highest probability of being reflected and re emitted. At present, the global average albedo (technical term for reflectivity) of our planet is 0.30, which means that 30% of the incident light is reflected back into space. But if the earth is a deep-water ocean, our albedo will be only 0.11. The ocean is actually very suitable for absorbing sunlight!
Bi hemispheric global composites from moderate resolution imaging spectrometer (MODIS) data taken in 2001 and 2002. Please note that it is our ocean, only our ocean, which makes our planet look blue in space.
The sky and ocean are not blue by reflection; They are all blue, but they all have their own will. If you take away our oceans completely, humans on the earth's surface will still see the blue sky. If you try to take away our sky (but still give us liquid water on the surface), our planet will still appear blue.
For the sky, blue sunlight is easier to scatter, so it shines on us indirectly from where the sun shines on the atmosphere. For the ocean, visible light with longer wavelengths is more easily absorbed, so the deeper they go, the darker and bluer the rest of the light appears. Blue atmospheres may be common for planets because both Uranus and Neptune have blue atmospheres, but we are the only planet we know with a blue surface. Maybe when we find liquid water on the surface of another planet, we won't be so lonely in many ways!
As we all know, there are seven colors of visible light: red, orange, yellow, green, blue, cyan and purple, but the wavelengths of light are different, and seawater is easy to absorb light with longer wavelengths, such as red, orange and yellow, while the corresponding green, cyan, blue and purple are not easy to be absorbed, especially blue and purple are most likely to be scattered and reflected, Therefore, when the sun shines on the sea, it is basically blue and purple.
So, the question comes, since the color of the sea is blue and purple, why do we see blue? It turns out that people's eyes are also very picky. They are very insensitive to purple and often turn a blind eye. They are just sensitive to blue. Therefore, in people's senses, the sea water is blue.
Why are some sea water blue and some green
The color of water depends on the absorption and reflection of light by water molecules. Sunlight is a mixture of seven colors of light, also known as spectrum. In the spectrum, the light near the wavelength range from red to green is easily absorbed by water molecules, and the light in the blue part will be reflected, so what we see is blue.
However, the color of the water is not always the same. The farther away from the center of the sea area along the coast, the sea water is dark blue, and some even purple. However, along the coastline near the land, the color of the sea water changes from blue to green and from green to yellow green. Why is there such a change? It has something to do with the floating matter in the water and the depth of the water.
Sea water can not only be described as blue. The color of the sea in different places will also change a lot. Near the coastline, there are a lot of organic matter and aquatic biomass from the land in the sea, including some small green substances called plankton. They contain a chemical substance of chlorophyll, which can absorb most of the red and blue light and reflect green light, So we see that the sea water along the coast is green.
In the universe, the color of the ocean allows us to distinguish the gathering area of life on earth. The green ocean area is like the tropical rain forest on land, full of life; The dark blue sea is a place where there is little life. It is like an uninhabited desert on the mainland.
The absorption of light by seawater and planktonic substances in seawater will also change the color of the water surface. Suppose you are driving a yellow submarine. Near the water surface, your submarine is yellow, but the submarine slowly dives into the seabed and less and less light shines on the submarine. When the submarine drops to a depth of 30 meters underwater, almost all the yellow, orange and red lights in the sun are absorbed by water molecules. Only the blue and green lights can reach the surface of the submarine, and then your submarine becomes blue-green. If you go down again until the green light disappears, the submarine will turn dark blue.
The more plankton, the more turbid the sea water, and the more light it absorbs. So the more turbid the water is, the faster you will see the surrounding environment darken as you descend.