Question

why night appear dark ?​

Answer 1

Answer:

During the day, sunlight floods our atmosphere in all directions, with both direct and reflected sunlight coming to us from everywhere we can see. At night, the sunlight doesn't flood the atmosphere, and so it's dark everywhere in the sky that there isn't a point of light at, like a star, planet, or the Moon.

Answer 2

Because earth rotate (and complete one rotation in one day) and the sun is present at only one side of earth then another part of earth have no sun light

due to this one side of earth appear night (darkness)