Why sunsets and sunrises appear red and orange

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Everyone loves a good sunset and sunrise. The beautiful colors of red and orange appear in the sky and everyone takes out their cameras and snaps a photo. But, have you ever wondered why the sky appears red and orange?

Earlier today we talked about why the sky is blue. For more details on why the sky is blue click here.

We will be talking about visible light and color wavelength. The visible light is made up of different wavelengths. Each color has its own wavelength, ranging from blue (short) to red (long). The color red has the longest wavelength of visible light. The size of red’s wavelength is 700-635 nanometers (nm) and violet (a shade of blue) has the shortest at 450-400 nm.

Image Credit: National Weather Service

Sunsets and sunrises appear orange and red because the color blue becomes scattered. The visible light hits millions of particles in the atmosphere and the particles scatter (change the direction) of the light. So instead of the light traveling straight and reaching the ground (your eye), it hits the particles and goes in all directions. This washes out the color. The smaller the wavelength is the easier it is to become scattered. This leaves behind the larger wavelength colors like red and orange to reach your eye.

Image Credit: NOAA/NWS Storm Prediction Center

Particles like dust, sand, dirt, and pollution in the lower atmosphere help provide the bright red and orange colors. Those particles are larger in size compared to the gas particles in the upper atmosphere. The red and orange wavelengths need larger particles and more particles for their wavelengths to become scattered and seen.

The sunlight has to travel through more of the lower atmosphere because of the lower angle of the sun. The lower angle plus all of the particles scattering the red and orange wavelengths causes the beautiful sunsets and sunrises that we see.

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