freefall

Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?

On Tue, 02 Dec 2008 02:32:56 GMT, "White Space Trash"
wrote:

Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?

I'd say neither, although it kind of depends on your definitions of
"suspended" and "freefall".

Every star in the Universe is in motion with respect to every other
star. Each star has a trajectory determined by its past history and by
its (complex) gravitational field environment. You might call that
freefall in the sense that the stars are freely acted upon by gravity,
without opposing forces. But that's a bit of a stretch of the
definition, IMO.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On Tue, 02 Dec 2008 02:32:56 GMT, "White Space Trash"
wrote:

Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?

I'd say neither, although it kind of depends on your definitions of
"suspended" and "freefall".

Every star in the Universe is in motion with respect to every other
star. Each star has a trajectory determined by its past history and by
its (complex) gravitational field environment. You might call that
freefall in the sense that the stars are freely acted upon by gravity,
without opposing forces. But that's a bit of a stretch of the
definition, IMO.

Actually, it's no stretch at all: it's precisely *the* definition of
free fall.

http://en.wikipedia.org/wiki/Free-fall

--
Dave

"White Space Trash" wrote:

Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?

Free fall simply means motion due to gravity alone. The stars are in
free fall within space. As such, the stars are suspended in the same
manner that the Moon is suspended over the Earth. The Moon is in free
fall within the Earth's gravitational field, but the Earth's surface
keeps curving out from under it.

The stars, however, do not orbit the Earth, but each other. Their
largest motion with respect to the galaxy comes from obiting the
galactic center of mass. But they also wiggle around to some degree
as they pass by one another. It's not a clean system: there are so
many sources of gravity in the galaxy, all interacting with each
other, that stellar motion is not entirely well ordered; it's more
like organized chaos.

The thing to remember is that the distances are so great that hardly
anything happens on a human time scale. For example, it takes the Sun
about 225 million years to complete one orbit around the Milky Way.

Although intergalactic velocities are greater, the distances between
galaxies is greater still, so it takes even longer for noticeable
stuff to happen on that scale. For example, it's currently thought
that in about 3 billion years, the Milky Way will either collide or
make a near miss with the Andromeda galaxy.
--
Dave

On Tue, 02 Dec 2008 01:19:45 -0500, Dave Typinski
wrote:

Actually, it's no stretch at all: it's precisely *the* definition of
free fall.

But in common usage it is generally used to refer to a small body
captured in the field of a large body. That's why I'd tend to avoid the
usage for describing the Universe as a whole, where objects influence
each other's motions, often without being gravitationally bound.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Dec 2, 4:55*pm, Chris L Peterson wrote:
On Tue, 02 Dec 2008 01:19:45 -0500, Dave Typinski
wrote:

Actually, it's no stretch at all: it's precisely *the* definition of
free fall.

But in common usage it is generally used to refer to a small body
captured in the field of a large body. That's why I'd tend to avoid the
usage for describing the Universe as a whole, where objects influence
each other's motions, often without being gravitationally bound.
_________________________________________________

Chris L Peterson
Cloudbait Observatoryhttp://www.cloudbait.com

Isaac thought so too ! -

"Cor. 2. And since these stars are liable to no sensible parallax from
the annual motion of the earth, they can have no force, because of
their immense distance, to produce any sensible effect in our system.
Not to mention that the fixed stars, every where promiscuously
dispersed in the heavens, by their contrary actions destroy their
mutual actions, by Prop. LXX, Book I."

The worse part of that statement Chris is that Isaac does not know
that the framework he built on has the stars organised in an
equidistant celestial sphere bubble ,this framework built on the
equatorial coordinate system -

http://apod.nasa.gov/apod/image/0609...hambsch_f1.jpg

http://www.opencourse.info/astronomy...phere_anim.gif

Isaac was a mathematician and could not have known that the
astrological framework is built on a false premise and conclusion -

"... our clocks kept so good a correspondence with the Heavens that I
doubt it not but they would prove the revolutions of the Earth to be
isochronical..." John Flamsteed

All this boils down to not knowing the basic value for rotation
through 360 degrees and subsequently not knowing what causes seasonal
variations in daylight/darkness.Instead of appreciating the spectacle
of the last few nights in true heliocentric terms where all get a
chance to consider our orbital position between Venus and
Jupiter,there is nothing but the dull and dismal silence

White Space Trash wrote:
Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?


They're all suspended in space from a giant invisible christmas tree ...

On Dec 2, 9:14*pm, lal_truckee wrote:
White Space Trash wrote:
Are all stars in the universe suspended in space or are they in somekind of
freefall that makes them appear to be suspended?

They're all suspended in space from a giant invisible christmas tree ...

Unfortunately when you live by the Ra/Dec system ,all motions of
foreground objects as pinned to that celestial sphere bubble like
ornaments on a rotating Christmas tree and it is great as a
'predictive' observational convenience ,at least up to a point, but
catastrophic for just about everything else from structural and
timekeeping astronomy to climatology and geology among other things.

As a race,thanks to the empirical hijacking of astronomy,we have
descended to a level where there is no such thing as
authority,responsibility ect.

So,have you got that straight,you may as well believe in an invisible
Christmas tree because what all here believe is not much different
given its astrological setup ,that is not a complaint but simply a
100% observational fact.

Chris L Peterson wrote:

On Tue, 02 Dec 2008 01:19:45 -0500, Dave Typinski
wrote:

Actually, it's no stretch at all: it's precisely *the* definition of
free fall.

But in common usage it is generally used to refer to a small body
captured in the field of a large body. That's why I'd tend to avoid the
usage for describing the Universe as a whole, where objects influence
each other's motions, often without being gravitationally bound.

Fair enough; I do see what you're getting at.

However, that brings up a problem. Namely, if we decide not to
describe the major components of the universe as being in free fall,
how else should we describe the situation?

One thing that peeved me no end in high school were science books that
made all manner of convenient approximations and analogies without
saying so. By the time I got to college, I had to un-learn half the
stuff I thought I already learned. What a waste of time. I've always
felt that if the authors would have simply said what they meant,
things would have been a lot easier.

So, that's the way I try to write: I try to use the correct terms and
insert parenthetical explanations where the audience might find them
useful. I do not eschew technical terms for the sake of
accessibility. In my opinion, avoiding the proper terms can confuse
and mislead the reader.

It doesn't always work out. When it doesn't, I think it's better to
err on the side of accuracy. My target audience is intelligent,
capable, yet not necessarily well-educated people. That is, people
who have the ability and desire to understand, but have not yet
understood.

Hm. I hadn't intended on this turning into a rant on pedagogical
practices, so perhaps this is enough. 8^)
--
Dave

oriel36 wrote:

As a race,thanks to the empirical hijacking of astronomy,we have
descended to a level where there is no such thing as
authority,responsibility ect.

Don't forget communism, terrorism, peace without honor, and the fact
that it's difficult to find decent potato salad in the South.

The universe is the answer. The question, however, remains unknown.
(but we /are/ chipping away at it)
--
Dave