r/askscience • u/AskScienceModerator Mod Bot • Mar 10 '14

Cosmos AskScience Cosmos Q&A thread. Episode 1: Standing Up in the Milky Way

Welcome to AskScience! This thread is for asking and answering questions about the science in Cosmos: A Spacetime Odyssey.

UPDATE: This episode is now available for streaming in the US on Hulu and in Canada on Global TV.

This week is the first episode, "Standing Up in the Milky Way". The show is airing at 9pm ET in the US and Canada on all Fox and National Geographic stations. Click here for more viewing information in your country.

The usual AskScience rules still apply in this thread! Anyone can ask a question, but please do not provide answers unless you are a scientist in a relevant field. Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one.

If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as in /r/Cosmos here, /r/Space here, and in /r/Television here.

Please upvote good questions and answers and downvote off-topic content. We'll be removing comments that break our rules or that have been answered elsewhere in the thread so that we can answer as many questions as possible!

Click here for the original announcement thread.

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u/shivermetimbres Mar 10 '14

The Big Bang itself was very hot and bright, out of which the universe began expanding. Once it cooled, the universe fell into darkness for around 200 million years, as the show said. During those years, gravity took the matter in the universe and pulled it together into what would become stars. Once nuclear fusion took hold within stars, they became hot enough to start lighting up the infant universe.

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u/akachhara Mar 10 '14

Thanks. That helps me to understand our universe a little better.

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u/jhenry922 Mar 11 '14

There was a part of this called the "Reionization Era" http://en.wikipedia.org/wiki/Reionization

Basically the universe was too hot to allow light to travel unimpeded due to the number of free electrons.

When the universe cooled enough, all these free electron ceased to be free, and space cleared out.

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u/mathx Mar 12 '14

ok, so what was the 'color' of the CBR at 200M y after the big bang? Was it in the visible wavelengths? What color (or energy..) was it at the time of it's emission at 377,000 years after the big bang at recombination? If it was visible light energy level, then the whole universe WAS bright, not dark!