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Why is the sky blue?
Air molecules scatter blue light far more than red, so wherever you look, mostly scattered blue light reaches your eyes. Physics 1.
The Duowenwen team · Updated
The sky is blue, not because air itself is blue, but because air scatters the blue part of sunlight all over the sky. This is a chain in the question map for middle school physics: Why, Then, What if. Three questions in all.
Why is the sky blue?
Sunlight contains every color. The molecules in the air are tiny, and they scatter blue light much more strongly than red light, so whichever direction you look in the sky, what reaches your eyes is mostly scattered blue light. Violet light is actually scattered even more strongly, but there's less violet in sunlight to begin with and our eyes aren't very sensitive to it, so what we see is blue rather than violet.
What if…?
What about when the Sun goes down? It's the same air and the same sunlight, so why are sunsets red?
Next: open the next question, "Why are sunsets red?", or type your own "What if…?"