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Author Topic: Why do some celestial objects form flat planes and some spheres?  (Read 2799 times)

Offline morgan

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Galaxies and the solar system (and presumably other solar systems) are always depicted as being flat or in the same plane, rather than having rotating objects at differing degrees in relation to the point of rotation.

Stars, planets are formed by matter collapsing around a point and gravity ensures a spherical shape.

Why do the former form discs and the latter spheres? Is this due to the size of the object, or the nature of their formation?

Thank you for your thoughts,


 

Ethos

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Galaxies and the solar system (and presumably other solar systems) are always depicted as being flat or in the same plane, rather than having rotating objects at differing degrees in relation to the point of rotation.

Stars, planets are formed by matter collapsing around a point and gravity ensures a spherical shape.

Why do the former form discs and the latter spheres? Is this due to the size of the object, or the nature of their formation?

Thank you for your thoughts,
It all depends upon the speed of rotation and the mass residing at the center of the object. One thing you may not have considered is that the Earth is also flattened at the poles which makes it less than completely spherical in form. The reason for this is also, the speed of rotation, centrifugal force by another name.
 

Offline RD

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Jupiter is noticeably oblate (bulges out at equator) ...



http://news.cnet.com/2300-11397_3-6162881-2.html?tag=mncol
« Last Edit: 28/05/2009 21:16:00 by RD »
 

Offline LeeE

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Galaxies range in shape from irregular, through the disk shaped spirals, to spherical (elliptical).  The largest galaxies observed are elliptical.
 

Offline Soul Surfer

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For strongly bound structures of interacting particles.  The lowest energy structure is approximately spherical.  rotation causes this to become oblate or bulging at the equator.
for weakly bound collapsing and rotating structures of interacting particles the preferred shape tends to be a disk because that minimises the likelihood of interactions between the particles
 

Offline LeeE

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There's also the fact that the average motion of any number of random motions is unlikely to be exactly zero.  The larger the number of motions averaged, the smaller the degree of residual non-zero motion, which seems to fit with the larger galaxies being elliptical.  Hmm...
 

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