Science Puzzle
Where Do the Stars Go in the Daytime?
On a clear night the sky is full of stars. Look up at midday on a clear day and there isn't a single one to be seen, just blue sky and the Sun.
Where do the stars go during the day?
The Answer
Nowhere. They're all still up there, shining just as brightly. The daytime sky is simply far too bright for us to see them.
During the day, sunlight hits the air and gets scattered in every direction, mostly the blue part of it, which is why the whole sky glows blue. That glow is millions of times brighter than the faint light from a distant star. The starlight still reaches your eyes, but it's swamped, in the same way that a torch beam that would light up a dark room is almost invisible outside on a sunny afternoon.
Take the bright sky away and the stars reappear even at midday. During a total eclipse of the Sun, the Moon blocks the sunlight, the sky darkens, and the brightest stars and planets pop into view. On the Moon, which has no air to scatter light, the sky is black even when the Sun is up.
It also explains why we see different constellations at different times of year. At night we look out away from the Sun. The stars on the Sun's side of the sky are up during the day, hidden by the glare, until Earth's journey round its orbit brings them into the night sky months later.
The principle: Contrast. A faint light can't be seen against a much brighter background, and scattered sunlight makes the daytime sky far brighter than the light of the stars.