during the day, the nitrogen in the air reflects the blue from our sunlight, so the sky is blue.. . during the night, the other stars are so far away, the light scatters and is absorbed by particles and dust in outer space. . . try this, shine a flahslight directly in your face, (close like our sun). . now shine twenty flahslights from the other end of a football field. (light doesnt combine like water or gas)