The reason behind day and night is the Earth rotates around the sun and the sun shines on one side of the Earth.

On the side that the sun is not shining on it, it is night. the moon has 7 seas made of dried lava. We mostly see the moon during dark but some times we see it during the day.

the earth is the only planet that is capable of supporting life (so far as we know).The earth spins once every 24 hours. The sun lights our earth and gives us basic light.