Why is the Night Sky Dark? | Neil deGrasse Tyson Explains...

Why is the sky dark at night? On this explainer, Neil deGrasse Tyson and Chuck Nice go over Olbers’ Paradox and why the night’s sky is dark. Hint: it’s not just because it’s nighttime.

Why isn’t the entire night’s sky ablaze with stars? We travel back to the early 1800s to discover ​​Heinrich Wilhelm Olbers’ confounding question: if the universe is infinite, shouldn’t every sightline land on a star? We discuss physics and equations for star brightness. If you put the sun three times farther away how much area in the sky does it take up? How did discovering the expanding universe finally help confirm this question?

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Science meets pop culture on StarTalk! Astrophysicist & Hayden Planetarium director Neil deGrasse Tyson, his comic co-hosts, guest celebrities & scientists discuss astronomy, physics, and everything else about life in the universe. Keep Looking Up!

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0:00 - Introduction
0:52 - Surface Brightness
4:12 - Olber’s Paradox
6:16 - Hubble’s Discovery
7:40 - How Light Travels
10:38 - Closing Notes

[thechosenone]

I got kicked out of a Flat Earth Facebook group for asking if the social distancing rule pushed anyone over the edge yet

[TheRabbitRonin]

I love it when they edit in a visual of what they are talking about because I have a hard time visualizing in my head what they talk about. Thank you for that!

[originalhazelgreene]

I love how well Chuck brings it down to my level.

[sir_charles_iii]

I love that Neil has a sense of humor. With great intelligence often people lose it and are condescending. He amazes me every episode.

[francoismenard]

The chemistry between these two guys is so fun to watch. They could be talking about anything it would still be interesting and funny.

[ScourgeZer]

Fascinating explanation! It’s always astonishing how we take things like this for granted, and that most of us don’t know such an amazing thing happens every night!

[Bad.Example]

I got to tell you, I came to this video with little expectation, but it blew me away. Great material

[TheRealMadDogMac]

Thank you! I love these videos… please, don’t ever stop doing these 🙏🏻

[huepix]

I've always loved how science makes huge discoveries from the most simple questions.
why does the apple fall down?
why is the night sky dark?
why is water wet?
and the answers are constantly mind expanding.
my personal question is why do we assume the universe expands as a single unit.
my hypothesis is that discreet areas of space, energy fields, are expanding into each other.
this concept allows for a unification of the fundamental forces and doesn't require a "big bang".

[jwmmitch]

I think I missed something about the inverse-squared law. The way he described it sounded like it would be 1/9 * 1/9 = 1/81, not canceling out. Imma hafta figure out what I missed

[jimr]

Thank goodness for Chuck. Throughout my academic career, I was always a "history/English" nerd. I never did too poorly in any subject, and perhaps it was the teachers and their particular style of teaching, but science/math was simply never my forte. And, so, I am thankful for Chuck. Neil explains all the mathematical intricacies of a topic, and I kinda sorta get the general gist of what he's saying. But then Chuck comes along and reiterates it in a way that even a simpleton like me can understand.

Thank you both for the service you provide us! StarTalk, truly, deserves to be classified as a public service and, as such, receive public funding. This show brings such interesting, useful, and fun information to us, and I really am so thankful.

[theCodyReeder]

The entire sky is glowing with very little variation. It’s just red shifted into the microwave. 😅

[ra]

OMG LOL Chuck is on it out the gate. This is going to be another great episode.

[BigDaddyMarkus]

I have to watch all of these SmartTalk videos 3-4 times so I can understand and remember all the info they give. I am very thankful for these videos.

[ricz]

When I read the video title I thought it was obvious but then I remembered that Neil always makes things interesting.

[ZuluBlackout]

I just can’t explain how much I love Neil and his brain. It’s so absolutely beautiful, I think I could have hours of conversation.

[jakegilbert]

You two have the best chemistry! Teaching, learning & laughing! It’s fantastic! Love you both!

[bertdrake]

No matter what kind of mood I am in. Y’all bring the humor and brighten things.

[ashutosh]

I don't know why but I literally clapped at the end of the explanation. Like always an awesome video, NDT explanation is just beautiful.

[RetNemmoc]

In an expanding universe, have we ever observed a galaxy going dark as it moves beyond visible range? E.g., a very dim and red-shifted galaxy appearing on early deep field photos that does not appear on recent ones.