MadSci Network: Astronomy

Re: Why do the sun rotate

Date: Mon Aug 3 14:59:20 1998
Posted By: Everett Rubel, Degree in Physics
Area of science: Astronomy
ID: 901010688.As


Thanks for the question.  I can answer it, but in the process with just 
raise another.

The Sun rotates because the material that it is made from already had some 
"rotation" built into it.  The quantity that is used to keep track of 
rotation in changing situations is called angular momentum.  The idea of 
angular momentum is that it is not just the amount of mass and the rate of 
rotation that is important, but also how spread out the mass is.  Before 
the Sun formed, the material of the proto solar system was fairly spread 
out compared to how it is now. It probably took centuries or millenia for 
this cloud to make one revolution. As this material pulled together and 
became concentrated into the Sun and planets, it had to maintain its 
angular momentum.  The mass stayed the same, so everything had to rotate 
faster.  This is just like the situation where a spinning ice skater can 
spin more rapidly by pulling their arms in close to their axis of rotation. 
  The Sun and almost all the planets all spin and/or rotate in the same 
direction, because they all came from the same spinning cloud of gas and 

So why did the cloud that formed the Solar system have angular momentum?  
This is still an open question, but if you look up "solar system 
formation", or "stellar nurseries", or "nebula", you may have what you are 
looking for.


Everett Rubel

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