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Apr 25 2009 10:26am
Quote (CeMeTeRy @ Wed, Apr 22 2009, 07:01am)
The basic reason why the planets revolve around, or orbit the sun (rotate actually is used to describe their spin, for example, the Earth completes one rotation about its axis every 24 hours, but it completes one revolution around the Sun every 365 days), is that the gravity of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth's gravity, the Earth orbits the Sun because of the pull of the Sun's gravity


sources:
http://curious.astro.cornell.edu/question.php?number=416



Doesn't have much to do with their rotation.

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Apr 25 2009 11:29am
I'm guessing that when planet/suns/whatever form it is from clouds of matter that gather near each other due to gravitation attraction and as they formed they do so in a circular type orbit and they gradually condense more and more. This rotation of matter would have the new planet containing to rotate like the mass was and then the conservation of angular momentum would apply. Objects colliding into planets can also affect the spin of the planets.

http://www.astronomycafe.net/qadir/q50.html
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Apr 26 2009 02:44am
Quote (Duress_x @ Sat, Apr 18 2009, 01:59am)
If I were you, I wouldn't question other people's education, with your senior thesis being like this

http://forums.d2jsp.org/index.php?showtopic=30450208&f=266

:wacko:


I completely agree with this statement.
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Apr 27 2009 07:40pm
Quote (BovineDesi @ Tue, Apr 21 2009, 07:16pm)
*sigh*.. okay, take a die and pick a side (lets say 6). Now take anything else, put it somewhere and take your die and rotate it around that object while the 6 is facing towards the center. If you notice, you can't have the 6 facing the center ALL the time without TURNING the die on its axis...

All planets rotate on their axis my friend.


Atleast, you understand... These people make me laugh.

thankyou for explaining it so I didn't have to.
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Apr 27 2009 07:45pm
Quote (juliusjuice @ Wed, Apr 22 2009, 11:15am)
big fat f'ing fail. first off the fact that particles spin is a fairly new discovery. second, no no one knows how gravity works.


ill give you the basics of it. dark matter was dreamed up after discovery of the the rotation curve of a galaxy. -some unknown force was holding everything in place, there was not enough matter to keep the galaxy in tact by gravity as we know it. but recent experiments and phonomena (voyager craft) have suggested gravity reacts differently (stronger) at great distances and that newtonian physics does not apply outside of a solar system -or just needs to be tweaked. (newtonian physics works perfect inside our solar system). this also help explain how a supermassive black hole at the center of a galaxy can hold a star at its rim, some 50,000 light years away. this "tweaking" of universal gravitational theory would be very very slight, but over such amazingly large distances makes a collosal difference. this theory is called MOND modified newtonian dynamics.

next you will say "explain hubbles constant" (the distance between galaxies appears to be increasing at a rate of 70km per second over a distance of 3 million light years) -well, the possibility is that light itself is effected by stronger gravitational pull when it leaves a system -not that space is inflating at all. enough for now ill post link when i make thread.

no i dont necessarily believe this, it is very interesting. scources are 13 things that dont make sense-by michael brooks -great read and march 09 issue of astronomy monthly.


Yes, this I know... and No Hubbles constant, is no longer constant... but it does explain why, at any given time, we can only see 13.7 (or some such, was it 14 something?) billion lightyears out. the funny thing is, if we measure it, we can see further than there is time allowed, thus suggesting that there is a gravitational pull beyond what we can see, that is actually accelerating the photons of light traveling out.

Your right, it is all very odd, and very interesting. but this again, is still focusing on the idea that space is... rather linear.
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Apr 27 2009 09:19pm
cuz it spins
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Apr 30 2009 09:07pm
Quote (Duress_x @ Thu, Apr 16 2009, 05:46pm)
I'm taking an astronomy class in college and I'm loving it and I find it very interesting.

We're pretty deep into the course now, but strangely enough, we never came across this question.


Why do planets rotate? I know they revolve around the sun because of gravity, but why do they rotate? and why do they rotate a certain direction?

I tried googling for some answers, but I was still not very clear on the reason other than the fact that it has to do with physics..


It has to do with inertia & a gravitational pull keeping the object rotating.
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