Why is the night sky dark if there are so many stars?
Quick Answer
Because the universe has a finite age and is expanding, most starlight has not had time to reach us, and much of it is stretched into invisible wavelengths.
The Full Story
If the universe were static and infinite, every line of sight would eventually end on a star, making the sky bright at night. But the universe is about 13.8 billion years old, so light from the most distant regions has not had enough time to reach Earth. In addition, the expansion of the universe stretches distant light into longer wavelengths, reducing visible brightness. This classic problem is known as Olbers’ paradox and was historically important in cosmology.
Key Facts
YouTube Angle
Suggested video title for this topic:
"The night sky is dark for a reason bigger than stars."
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