Article is coming, but..
you find the answer fo the question - why is it dark at night?
You probably won’t believe but the answer is because the Universe is expanding. The full explanation of this problem is known as Olbers’ paradox or dark night sky paradox.
The more detailed explanation says that the darkness of the night sky conflicts with the assumption of an infinite and eternal static u. In the hypothetical case that the universe is static, homogeneous at a large scale, and populated by an infinite number of stars, any line of sight from Earth must end at the surface of a star, and hence the night sky should be completely illuminated and very bright. This contradicts the observed darkness and non-uniformity of the night.
The darkness of the night sky is one of the pieces of evidence for a dynamic universe, such as the Big Bang model. That model explains the observed non-uniformity of brightness by invoking spacetime's expansion, which lengthens the light originating from the Big Bang to microwave levels via a process known as redshift; this microwave radiation background has wavelengths much longer than those of visible light, and so appears dark to the naked eye. Other explanations for the paradox have been offered, but none have wide acceptance in cosmology.