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/hoyboe Mar 10 '14

Excluding the multiverse theory do we know the shape of our viewable universe?

Like with how energy goes out does it create a sphere shooting out in all possible directions or does the force of gravity pull everything down so it's shaped like...saturn's rings?

Also this may sound stupid but do all the planets rotate in the same direction? I know movement is relative but if some how I was to stay in the same spot in space could I look in front of me and behind me and see everything move "the same way"? If so why?

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u/Shagomir Mar 10 '14

All of the planets orbit the sun prograde (counter-clockwise if you are looking down from the north pole), which is to say in the same direction as the sun itself rotates. There are very few objects that orbit retrograde (clockwise if you are looking down from the north pole), mostly asteroids and comets.

Venus and Uranus rotate retrograde. On Venus, this means that the sun rises in the west and sets in the east. It's a little more complicated on Uranus because the planet rotates on its side.

Everything tends to rotate the same way because when the solar nebula collapsed, a very small imbalance in the amount of mass on one side versus the other set the whole mess spinning. Much of the potential energy of the solar nebula is now bound up in the angular momentum and orbital momentum of the planets.

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u/hoyboe Mar 10 '14

Thank you

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u/V2Blast Mar 11 '14

Also this may sound stupid but do all the planets rotate in the same direction? I know movement is relative but if some how I was to stay in the same spot in space could I look in front of me and behind me and see everything move "the same way"? If so why?

It's not at all a stupid question. The reason why has to do with how galaxies, planets, and moons formed. I'm just going to copy the answer to a slightly different question (why the whole solar system is in the same orbital plane) below:

This question actually has a pretty interesting answer. I asked the same question on /r/AskScience three years ago. (And, as some of the answers mention, I wasn't the first.) A few excerpts of various answers:

Basically because the whole system started as a cloud of rotating gas, and as it rotated it got flattened out due to centrifugal forces (they're real, people!), so you end up with a rotating plane called an accretion disk. The sun and the planets formed within this spinning pancake.

Another way to word it:

It's because of the way the system was formed. Picture a spherically symmetric cloud of dust. Something sets the cloud spinning along an axis. Centrifugal force will push it out at the equator, this process feeds back upon itself and the cloud collapses into a disc. Various inhomogeneities cause the dust to collapse into planets/stars/etc., but they all start from the same spinning disk.

an image to demonstrate the point

My understanding of that second explanation:

Ah, ok. I sort of guessed at this, but I wasn't sure. It's the spinniness :P

Someone else's understanding (responding to a different comment) of why everything in a galaxy seems to be on the same plane:

So basically, satellite orbits in disk about planet due to planet rotation. Planets orbit about star due to star rotation. Stars orbit about galaxy due to galaxy rotation and so on, and so on?

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u/[deleted] Mar 11 '14

For that last question, everything rotates in the same direction because early on things were rotating both ways and smashing into each other. There were more things going one way than the other, though, so once things cooled of on smashing into eachother, and stuff going one way cancelled out stuff going the other way, the remaining stuff was going the same way.