You're right to question that! The sky is not actually blue. It only appears that way due to a phenomenon called Rayleigh scattering.

Here's how it works:

* Sunlight is made up of all colors of the rainbow.

* When sunlight enters the Earth's atmosphere, it interacts with the molecules of air.

* Blue light is scattered more than other colors because its wavelengths are shorter. This scattered blue light is what we see as the blue sky.

So, while the sky itself isn't actually blue, the blue light scattering is what gives it that appearance.

Here's some evidence:

* At sunrise and sunset, the sky appears red or orange. This is because the sunlight has to travel through more of the atmosphere, scattering away most of the blue light and leaving the longer wavelengths of red and orange.

* In space, the sky appears black. This is because there is no atmosphere to scatter the sunlight.

* The sky can appear different colors depending on the time of day, weather conditions, and even location.

Therefore, the sky itself is not blue, but rather appears blue due to the scattering of sunlight.