Sunlight looks white.
But it is really made of all the colors of the rainbow.
You can see those colors in a rainbow.
Raindrops act like tiny prisms. They bend the light. They split it into its colors.
Light travels in waves, like waves in the ocean.
Each color has a different wave size.
Red light has long waves.
Blue and violet light have short, small waves.
Earth is surrounded by air. That air is called the atmosphere.
The air is made of gases, like oxygen and nitrogen.
It also has tiny bits of dust in it.
Light travels in a straight line. That changes when something gets in its way. Light can bounce off. Light can bend. Light can scatter.
When sunlight comes into the air, some colors pass straight through to our eyes.
Much of the red, yellow, and green light passes straight through.
Blue and violet waves hit the gas bits in the air. They bounce off.
They scatter in every direction, for all to see.
That scattered blue light is what hits our eyes from all over the sky.
So the sky looks blue.
Violet light scatters too.
But some violet light is taken in high up in the air.
Our eyes are also not as good at seeing violet as they are at seeing blue.
So we see blue most of all.
Look far away, near the horizon. The sky fades to a lighter blue or white.
Light from there has passed through even more air.
The blue light has been scattered so many times that less blue light reaches us.
When the Sun gets low, its light passes through more air to reach you.
Even more blue and violet light is scattered away.
Then the reds and yellows can pass straight through to your eyes.
Big bits of dust and water vapor in the air can scatter more reds and yellows too. Sometimes the whole western sky glows red.
A red box looks red because it takes in the other colors and bounces red back to our eyes.
Green grass is green because it bounces back green light.
The sky works in a similar way. We see the blue light that the air scatters to our eyes.
Sunlight often appears white, but it is actually made of many different colors with different wavelengths.
Some sunlight is visible to humans, like the colors of the rainbow. Some is invisible to the human eye, like ultraviolet light and infrared light.
Raindrops act as tiny prisms when lit by the Sun, bending light and separating it into its different colors.
Visible light includes the wavelengths our eyes can see. The longest wavelengths we can see look red to us. The shortest wavelengths we can see look blue or violet.
A red light wave is about 750 nanometers, while a blue or violet wave is about 400 nanometers. A nanometer is one-billionth of a meter. A human hair is about 50,000 nanometers thick, so these waves are very, very tiny.
Light travels in a straight line unless something gets in the way to reflect it, like a mirror, bend it, like a prism, or scatter it, like molecules of the gases in the atmosphere.
Earth is surrounded by an atmosphere made up of many gases, such as oxygen or nitrogen, and little particles of dust or other things that exist in the air.
When we see an object as a specific color, some wavelengths of light are absorbed by the object, but others are reflected. A red box reflects the red wavelength. Green grass reflects the color or wavelength of green light.
Gases and particles in Earth's atmosphere scatter sunlight in all directions. Blue light is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.
As white light from the Sun enters Earth's atmosphere, much of the red, yellow, and green wavelengths, mixed together and still nearly white, pass straight through the atmosphere to our eyes.
The blue and violet waves are just the right size to hit and bounce off the molecules of gas in the atmosphere. They become separated from the rest of the light and scattered in every direction.
The other wavelengths stick together as a group, and therefore remain white. The scattered violet and blue light dominates the sky, making it appear blue. This scattering is called Rayleigh scattering.
Some of the violet light is absorbed by the upper atmosphere. Also, our eyes are not as sensitive to violet as they are to blue, so the sky appears blue rather than violet.
Closer to the horizon, the sky fades to a lighter blue or white.
The sunlight reaching us from the horizon has passed through even more air than the sunlight reaching us from overhead. The molecules of gas have rescattered the blue light in so many directions so many times that less blue light reaches us.
As the Sun gets lower in the sky, its light passes through more of the atmosphere to reach you. Even more of the blue and violet light is scattered, allowing the reds and yellows to pass straight through to your eyes without all that competition from the blues.
Also, larger particles of dust, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows, sometimes making the whole western sky glow red.
Sunlight carries the energy that heats Earth and powers all life on Earth. Our climate is affected by how sunlight is scattered, reflected back to space, or absorbed by forests, deserts, snow- and ice-covered surfaces, different types of clouds, smoke from forest fires, and other pollutants in the air.
Satellites can perform what is called remote sensing from space. Instruments on satellites such as the Geostationary Operational Environmental Satellites-R (GOES-R) Series can measure the intensity of light of different wavelengths. Analyzing that information, scientists find out surface and atmospheric temperatures, and levels of carbon dioxide, water vapor, pollutants, ozone, and other trace gases.
NOAA National Environmental Satellite, Data, and Information Service (NESDIS), “Why Is the Sky Blue?” (nesdis.noaa.gov). Content produced by the NASA Space Place team at NASA's Jet Propulsion Laboratory for NESDIS.
Smithsonian Science Education Center, “Why is the Sky Blue?” (ssec.si.edu).
Checked November 2, 2026