If you could stand on the moon and look at the sky, it would always be dark black. This is because the moon has no air. If the earth had no atmosphere, our sky would stay dark, too. Instead, the sky over the earth is dark only at night when the sun doesn’t shine.
Sunlight is made up of red, orange, yellow, green, blue, indigo, and violet light. These colours scatter when they hit the earth’s air. Some of them scatter more than others. Red, orange, and yellow light scatter the least. Blue scatters so much that it spreads to fill the sky.
That line in the distance where the sky seems to meet the earth is called the horizon. When the sun is near the horizon, sunlight must travel further through our atmosphere. This makes blue and most other colours scatter too much to be seen. But red, orange, and yellow are scattered just enough to make a beautiful sunrise or sunset. Dust from pollution, forest fires, and volcanoes can help make a brighter red or orange sunrise or sunset. The dust makes the other colours scatter even more.