Why Is the Sky Blue?
Sunlight is a rainbow in disguise
The light that comes from the Sun looks white or yellow, but it is really a mix of every colour — red, orange, yellow, green, blue, indigo and violet, all travelling together.
Each colour moves like a wave. Red light makes big, lazy waves. Blue light makes small, fast, bouncy waves.
Bouncing through the air
Our air is full of tiny gas bits called molecules. When sunlight hits them, the light scatters — it bounces off in all directions.
The small, bouncy blue waves get scattered much more than the big red ones. So blue light goes bouncing all across the sky, and that is the colour your eyes see almost everywhere you look up.
So why are sunsets red?
At sunset the Sun is low, so its light travels through much more air to reach you. By then most of the blue has bounced away, leaving the reds and oranges to glow across the sky.
💡 Did you know? On Mars the sky looks butterscotch-pink during the day and bluish near the setting Sun — the opposite of Earth — because of the dust floating in its thin air.
🧪 Try this at home: Shine a flashlight through a glass of water with a single drop of milk stirred in. From the side the water looks faintly blue; from the front the light looks orange — the same scattering that paints our sky!