Question

why the sky appears blue in day time while black at night?

Answer 1

The sky appears blue in day time because the molecules in the air scatters blue light from the sun more than they scatter red light.

Answer 2

The sky appears black at night because there are no scattered light to reach the eyes of an observer during the night. We get a clear (view of space, which is black.

Answer 3

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This will also help you: http://www.tellmewhyfacts.com/2007/11/why-is-sky-blue-in-day-and-black-at.html