Why the sky looks blue — Earth science, 7–10 years
Sunlight looks white, but it contains many colours. Air spreads blue light around the sky more strongly than most other colours, so blue reaches our eyes from many directions.
White sunlight, scattered blue
Sunlight is a mixture of colours, even though our eyes often see it as white. When it travels through the atmosphere, tiny air molecules bump into the light and scatter some of it. Blue light is scattered widely, so the whole sky seems blue when the Sun is high.
Why the sky has a colour
People wanted to understand why the sky was not simply dark or the exact colour of the Sun. The answer came from studying light and the air around Earth: the atmosphere changes the path of some colours. It also explains why the Sun can look orange or red near the horizon, where its light crosses more air.
Comparing midday and sunset
At midday, sunlight may travel about 10 kilometres through the atmosphere to reach you. Blue light is scattered along the way and arrives from across the sky, so the sky looks blue. Near sunset, the light travels through much more air, perhaps 100 kilometres or more, so much of the blue scatters away before the direct light reaches you.
It is not a reflection of the sea
A common mistake is to think the sky is blue because it reflects the sea. That seems reasonable when you look at blue water under a blue sky, but the sky is also blue above deserts and far from oceans. The colour comes mainly from sunlight being scattered by air molecules.
Reading the sky
The same scattering helps explain red sunsets, pale skies on hazy days and the colour seen in many photographs from space. Astronomers and scientists study how light changes as it passes through air and dust. A sunset is not a different Sun; it is sunlight taking a longer route through the atmosphere.
Keep exploring
Other languages
Loading MyLeoNes™…