First of all, you must know that light can be observed as a wave and as a particle. As a wave, it has a wavelength, and different wavelenghts create what we see as colors. For example, red has the longest wavelenght. If we see that something is red – it actually means it’s everything but red. That’s because it absorbs every wavelenght different than the wavelenght of the color red. As a result, the object emmits only light with the longest wavelenght – and we see it as red. As you can see in the picture, the object absorbed the blue and green light, but reflected the red.
When we look up at the sky, we can see that it’s obviously blue. What we don’t see is billions and billions of tiny little particles (atoms, molecules, etc) floating around. When sunlight travels through air, longer wavelenghts slip on by, but shorter wavelengths (blue has a short wave lenght) collide and interact with air molecules – which causes them to emmit blue light.
During sunrise or sunset, there are even more air particles separating us and the Sun (than there are at noon, for example). As a result, light bounces randomly in all directions, and almost all wavelenghts are scattered around, except for the longest wavelength – the red. That’s why particles then reflect the color red, and we see sunrise and sunset as a combination of different shades of red.
Napisala: Mateja Napravnik