Flexi Says: During the day, the sky looks blue because the light from the Sun, or closest star, is scattered by the gases in Earth's atmosphere into all of the colors that make up white light. Blue wavelengths scatter the most and enter our eyes more than the other wavelengths, so we see the sky as blue. On the other hand, during the night when that part of Earth is away from the Sun, there is no nearby source of light that can be scattered by the atmosphere and that is why the sky looks black. Although space is full of stars, it still appears dark and not bright. This is known as Olber's paradox. The dark appearance of space can be explained by considering that the universe is approximately 13 billion years old and thus we can only see those objects that are as far as the light can travel in 13 billion years. Beyond that, the light from stars will not reach us, and thus space looks black.
