Curious Kids: why do we see the 'sky' during the day, but the galaxy at night? - The Conversation AU

To put it simply, the reason the sky looks different to us between daytime and nighttime is mostly because of our atmosphere.

Some of the molecules in Earth’s atmosphere are just the right size that the blue part of the light from the Sun bounces off them, scattering in different directions.

So when we look towards the Sun during the day (remembering that you should never look directly at the Sun), we see rays of light that have come from the Sun straight down to us.

But when we look away from the Sun we see the blue light rays scattering from the part of the atmosphere we are looking at.

At night we see stars in a dark sky, and these stars make up our galaxy, the Milky Way.

Compared with other stars, the Sun actually isn’t that bright, but it looks very bright to us because it’s much closer to Earth than other stars are.

At night, when your side of Earth is facing away from the Sun, the only light that reaches you is from other stars.

This starlight also scatters off molecules in the atmosphere, but as there’s less of it, not much scattering goes on.

This is why, at night when we’re facing away from the Sun, we don’t see the same thing as when we are facing the Sun during the day.

Instead, we can look through the atmosphere and beyond at the big, dark expanse of space around us and the many, many faraway stars in our galaxy

Other planets in our Solar System have different molecules in their atmosphere compared with Earth, which means their skies look different during the day and night

Astronauts who are above our atmosphere, such as on the International Space Station or on the Moon, don’t see the bright blue sky we see on Earth