Why Is the Sky Blue?

Have you ever looked up on a clear day and wondered why the sky is blue instead of, say, green or purple? It’s a question many of us have asked as children—and the answer lies in the way sunlight interacts with our atmosphere.

Sunlight might look white, but it’s actually made up of many colors. These colors can be seen in a rainbow and include red, orange, yellow, green, blue, indigo, and violet. Each color has a different wavelength, with red having the longest wavelength and violet the shortest.

When sunlight enters Earth’s atmosphere, it collides with molecules and small particles in the air. This causes a phenomenon called Rayleigh scattering. Shorter wavelengths, like blue and violet, scatter more easily than longer wavelengths like red and yellow. However, our eyes are more sensitive to blue light and less so to violet, which is mostly absorbed by the upper atmosphere. This is why we see the sky as blue during the day.

At sunrise and sunset, the sky often turns orange, pink, or red. That’s because the sun is lower on the horizon, and its light has to pass through more of the atmosphere. This longer path causes most of the blue and violet light to scatter out of view, leaving the reds and oranges for us to see

So, the next time you admire a blue sky or a colorful sunset, you’ll know there’s some fascinating science at play—showing us how beautiful physics can be.