The Real Reason Skies Go Dark After The Sun Sets

Why does the sky go dark at night? You are all probably thinking that this is a question even a kindergartner can answer - The simple answer and the one that is pretty obvious is that as the Earth rotate on its axis it moves away from the sun and therefore, causes the skies to go dark. Sounds logical to us but what about the zillions of sparkly stars? Why don't they pitch in and make the sky all shiny?

This was a question that German astronomer Heinrich Olbers pondered over at length all the way back in 1823. There were many possibilities - Maybe the light from the stars was being blocked by dust, but then that would also have the same effect on the sun. Then there was that possibility that maybe there were just not enough stars or that they were all stacked behind each other - Both facts that we all know are not true. 

After thinking about the conundrum at length, astronomer could only blame the darkness to one thing - the finite age of our Universe, or what scientists refer to as our Observable Universe. Since this according to the experts is estimated to be 13.7 billion years old, any light from stars beyond cannot be observed by us especially with our naked eyes, giving us the impression that the sky is dark. 

While this phenomenon called Olbers' Paradox is still considered to be the primary reason for the lack of light, when NASA's Hubble telescope discovered that our Universe was still expanding, scientists realized that there could also be another reason for our dark skies - The ever-growing Universe is pushing the stars further and further away, so much so, that millions of years from now, humans may not be able to see any stars unless they use infrared telescopes, because the speeding stars do leave behind a streak of faint infrared light!

Still a little confused? Then be sure to watch this easy to follow video put together by 24-year old Harry Reich. Scientifically trained in physics, Harry is is now focusing on cinematography and creating a series of videos dubbed Minute Physics that makes science simple and fun to learn, for those of us not as passionate about the subject.

Resources NPR.org, math.ucr.edu