Expert: Tom Whiting - 8/12/2009

Question
QUESTION: Why all the planets more or less lie in the same plane with the sun? Why can't they differ more angle with each other? Ex: Jupiter is revolving from top to bottom with respect to earth.

ANSWER: Hi s,
Nature and gravity tends to draw a rotating loose mass down into a pancake shape as the cloud
gravitationally collapses on itself over millions of years...so that's why all the planets are basically in the same plane. The initial cloud of dust and gas had some rotation to it.
So the matter outside the core region tends to migrate to a central, equatorial plane by gravity.

And for the same reason, our Milky Way galaxy is also a flat pancake shape, as are most of the rotating spiral galaxies too.  So it's the rotation.  If there is little or no rotation, then you end up with a spherical or elliptical shape, like the old elliptical galaxies we see out there, with very little initial rotational energy.
When galaxies collide, they tend to lose their flat pancake shape and become spherical or
elliptical because the collision partially destroys the rotational energy.
(Just like a nicely thrown spiral football pass, when touched or hit by a defending man's hand, tends to fly off course and begins tumbling through the air, losing it's nice spiral pattern
of flight).

The axis of rotation of a singular body, like Uranus axis tilted nearly 90 degrees, or Venus'
slow backward rotation...it thought to be caused by large meteorite impacts early on in the formation of those planets some 4-5 billion years ago. Perhaps that's why the Earth's axis
is tilted 23.5 degrees from the vertical...we also took some major meteorite hits, early on.
Hope this helps,
Clear skies,
Tom

FOLLOW UP:
And don't forget tonight is the magical night of August 11th...the Perseid meteor shower
max'es out tonight, 60-200 meteors per hour after midnight local time, with still 1/4
strength tomorrow night.
Clear skies,
Tom

---------- FOLLOW-UP ----------

QUESTION: Our milky way galaxy is spiralling. That means all the stars and planets are getting inside! Will our milky way galaxy ends up? What is actually in the centre of our galaxy and other? Is it black hole or any? I'm in india. And thank you for your "Follow up".

Answer
Hi Shameem,
Our Milky Way stars are not spiraling inward;
We call our galaxy (and all spiral galaxies)...a spiral galaxy because of it's appearance of arms....compared to old elliptical, spherical-shaped galaxies, but that doesn't mean the stars are spiraling inward.  Its just a name, a designation.  In fact, galaxies maintain a very stable rotation.  Our Solar System has made an estimated 18 trips (orbits) around the Milky Way since we formed up some 4.6 billion years ago and our distance of 25000 - 30000 lightyears from the center probably hasn't changed much over our 4.6 billion year lifespan.
Perhaps down near the core where there resides a very massive black hole, stars out several
hundred lightyears may be slowly spiraling down toward that black hole in the center, but
we are too far removed from the center to be affected by that.  

Actually, the latest data shows that we are not a regular spiral galaxy, but a barred spiral
with a central bar of stars through the center of the galaxy. (Like NGC 1073 or NGC 1300 -
you can google them.)

Our Milky Way galaxy is on a collision course with the famous Andromeda galaxy in about
5-6 billion years from now. Presumably the two will merge into one giant elliptical galaxy
after the collison, actually merger, is completed in about 7 billion years from now.
Yes, there is a massive black hole in the center of the Milky Way, as most large galaxies
now seem to have a very massive black hole in their centers.  Perhaps that is required in nature to help form up a large galaxy initially, and keep all 200 billion stars in a regular pattern and
group, and keep them from flying off into intergalactic space.
Clear skies,
Tom Whiting
Erie, PA