Why the sky is dark at night? Shouldn't it be completely illuminated because of an endless amount of stars?
Yes, if the universe were static and populated by an infinite number of stars, then every line of sight should end at the surface of a star. This would cause the night sky on Earth to be completely illuminated and very bright.
But the darkness of the night sky is one of the pieces of evidence for a dynamic universe, such as the Big Bang model. The space between light sources is always increasing.
The expanding universe lengthens the light of stars to microwave levels which appears dark to the naked eye. The expanding universe lengthens the light of stars to microwave levels via a process known as redshift which appears dark to the naked eye. This microwave radiation background has wavelengths much longer than those of visible light.
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