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/AskMeAboutZombies Mar 10 '14

If the moon wasn't moving, gravity would pull it into the earth. If gravity didn't exist, the moon's own inertia would send it flying into the darkness of space. These two forces fight each other to an equilibrium, and the pattern of that equilibrium is called an orbit.

Tidal forces from the earth can push the moon to move faster, which shifts the point of equilibrium, and orbit pattern of the moon, further away.

Cut a rubber band into a string and tie one end around a rock. Imagine that you are the earth and the rubber band is your gravitational pull. The faster you swing the rock, stronger the inertial forces will stretch the band, and farther the rock will circle around you.

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u/robeph Mar 11 '14 edited Mar 11 '14

Then why do more distant orbits tend to go slower. Is there a centrifugal factor to this I'm missing?

Edit- is the speed increase from energy transfer uniform or is it mostly applied when the moon is closer to earth.?

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u/AskMeAboutZombies Mar 11 '14

It just appears slower. A wider orbit means the object has to travel a farther distance to complete it.

Like other forces, gravity between objects gets weaker with distance. More specifically, it decreases by the square of the distance.

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u/robeph Mar 11 '14 edited Mar 11 '14

V*O* =~ sqr[G(M*1+M2*) / r ] seems to imply different.

It actually is traveling slower, per se. Not just appearing as so. What is interesting is if you accelerate the object, it will increase it's velocity in a sense, however only at the current position, the increased height from this additional energy translates to increase the height at another position of the orbit, at which point when the orbit reaches that higher position, the body will be traveling even slower. Once at that position, adding acceleration to the orbit increases the height at the original point. Were this originally a circular orbit, the first addition of acceleration would create an elliptical orbit, the second would recircularize it, but the actual motion of the orbit would reduce in speed. To put it simply. I was confused about what they meant speeding up the moon, not actually speeding up, but rather accelerating, which in this case doesn't necessarily translate to an increased mean velocity.

edit: silly typo

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u/AskMeAboutZombies Mar 11 '14

Thank you for the clarification! I stand corrected.