Expert: Tom Whiting - 4/16/2009

Question
why all planet moving around star(For example sun)in same direction? or satellite revolving around planet in same direction. and second question why stars , planet, satellite rotating on their axis?

Answer
Hi dinesh,
Guess I could answer, "Why not?"

Solar systems form out of a slowly rotating nebula of dust and
gas which slowly collapses and condenses.  If they didn't rotate, then wouldn't all the material fall directly into the central forming star?  Yes, it would. The star would have
no bodies orbiting it and probably have no, or slow, rotation.
Some stars are probably like that, with zero planets.

But if there is even the slightest rotation of the primordial nebula, then planets probably form and the system will end up with all the planets in roughly the same plane and orbiting the star in the same direction, the direction of the original cloud rotation...and same direction as the star's rotation.  Our Solar system is a fine example.

The planets orbit the star because of the initial rotation of the
cloud...as said earlier, if they didn't revolve around the sun,
then they just would have fallen into the newly forming sun and
been destroyed.
The planets rotate (approximately the same direction) because of eddies and currents set up at the time of their formation, along with their satellites. But not all do...Venus for example, rotates very slowly, backwards. That's why it probably ended up with no satellites..they all fell into the forming Venus with no, or too slow, revolution around Venus. Uranus' polar rotation is another exception, perhaps Uranus had an encounter with another body early on that changed it's direction of rotation.  There is no way to know
what exactly happened some 4 billion years ago.

Everything moves relative to everything else...there is no such
thing as 'absolute rest'....the Earth rotates and revolves around
the sun.... the sun revolves around the Milky
Way Galaxy, the galaxy moves within the Local Group (of galaxies)
and the Local Group revolves around the Virgo Supercluster.
So we are always in 'new' space, never to return to....past occupied
space...we are always cutting new ground as they say.

So it's only common sense that all the Solar System bodies are
in roughly the same plane, and revolve around the sun in the
same direction, and have at least a moderate rotation rate, nearly
all in the same direction.  I would think that it's weird...if they
didn't.  To me, Venus is the weird planet in that respect.

Not all satellites revolve around their parent planet in the same
normal eastward direction, like a few of Jupiter, Saturn, and Neptune's moons.  It's thought that those few moons were captured asteroids which occured at a later time, well after their initial formation.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA  USA

PS...it's not so much why, but how, when, and by what process. Who, and "Why"....are really philosophical or theological questions which we in science...don't answer.  Why are we here? Why is Saturn here?
Who put us here?  Why and who are technically theological questions.

Science answers the how,what, when, and by what process...questions, only.
For the who and why, you have to consult your religious or
philosophical advisor.  We stay out of their territory (the Who
and Why) and hopefully, they stay out of our territory,...the how,
what, when, and by what process...questions.  They are the experts
on the who and why....we in science are the experts on the other
questions.  Too often, they tend to stray into....our territory,
and that's when... big conflicts arise.  They need to stay out of
our territory, as we stay out of their territory.
Clear Skies,
Tom