Why is the sky blue during the day but dark at night?

The sky appears blue during the day because of the way sunlight interacts with the Earth's atmosphere. Sunlight is made up of a spectrum of colors, with shorter wavelengths like blue being scattered more easily by the gases and particles in the atmosphere. This scattering causes the blue light to be more visible and gives the sky its blue color.

At night, when the sun is no longer shining on the atmosphere, there is no light to scatter and the sky appears dark. However, we can still see stars and other celestial objects in the night sky because they emit their own light or reflect light from other sources.

During the day:

- Sunlight is composed of all colors of visible light.
- When sunlight enters the Earth's atmosphere, it encounters molecules of nitrogen and oxygen, which are much smaller than the wavelength of sunlight.
- These molecules scatter or bounce the sunlight in all directions.
- However, blue light (the shortest wavelength) is scattered more effectively than other colors. This is known as Rayleigh scattering.
- The scattered blue light reaches our eyes from all directions, giving the sky its blue appearance.

At night:

- When the sun sets, direct sunlight no longer reaches the atmosphere.
- The only light we see is from stars and the moon, which emit very little blue light.
- Without the scattering of blue light, the sky appears dark.