Why does the sky appear blue during the day but red at sunset?

The sky changes color because light travels through air, and different colors behave differently.

Imagine you're playing with a flashlight in a room full of tiny balls, these are like the particles in the air. When it's daytime, the light from the sun goes straight through the air to your eyes, just like when you shine your flashlight on the wall without any obstacles. The blue part of the light is more scattered by the tiny balls, making the sky look blue.

At sunset, the sun is lower in the sky, so its light has to travel through more air, like if you had to shine your flashlight all the way across a big room instead of just to the wall. This means more of the blue light gets scattered away, and the red and orange light stays behind, making the sky look reddish or orange.

It's kind of like when you put a red filter on your flashlight, only the red light comes through, and everything looks redder. That’s why sunsets feel so warm and special!