Weather Explainers

It Takes The Entire Rainbow Of Colors To Make The Sky Blue. Here's Why.

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The sky isn't just blue by chance.

It takes all the colors of the rainbow for us to see it that way.

It happens because of something called the Rayleigh effect, or Rayleigh scattering, named after a British scientist who first wrote about it in 1871.

Light breaks over the horizon at sunrise, seen in a photo from the International Space Station.
(NASA Astronaut Nick Hague via Instagram)

Our modern-day expert, weather.com senior meteorologist Chris Dolce, explains:

The white appearance of sunlight reaching the Earth actually comes to us in all colors of the rainbow, all of which travel in different wavelengths.

All of those colors are scattered when they encounter dust and tiny gas molecules in our atmosphere, however blue and violet are scattered the most. That's because blue and violet light have the shortest, smallest wavelengths.

Since the blue waves become separated from the rest of the light spectrum through this scattering effect, that's what we see with our naked eyes. And we see the blue light instead of violet light because our eyes are more sensitive to it and the sun emits more blue than violet energy.

Sunlight comes to Earth in a rainbow of colors.
(Photo Illustration by Hannah La/weather.com)

We also see the Rayleigh effect at play in:

-Sunsets where the sky is red. Light has to pass through a larger part of the atmosphere when the sun is lower on the horizon. Red, orange and yellow have longer wavelengths, which means, in short, they have a better chance of making the long journey.

-Wildfire smoke that turns the sky a hazy orange. In this case, smoke particles act as a catalyst that changes the way light scatters. That can leave us seeing less blue and more orange, although the effect can vary based on time of day and other factors.

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Weather.com staff writer Jan Childs covers breaking news and features related to weather, space, climate change, the environment and everything in between.