Happy Solstace

"|-|erc" wrote in message...
...

"Muff Diver" wrote...

So now having brushed against the tropic of cancer the sun is now
headed away from polaris and will turn around after brushing
against the tropic of capricorn and head toward polaris again ?

I always wondered, compared to a fixed point in space, what direction
and at what velocity is the center of mass of the sun, the theoretical
center of mass of our solar system, traveling.

Any astro-whatevers out there know? Or is the planet earth just going nowhere fast.? LOL !

Cross posted to alt.astronomy, the sun orbits the center of our galaxy,
in phase with all the surrounding stars so not like a planets orbit, something
like a 2 million year period if memory serves. galaxy speeds aren't given an absolute
speed in current models, though a relative figure against neighbouring galaxies
might be considered the absolute speed.

Herc

Mensa! Pleasure!

The first thing i noticed was the "center of mass of the Sun" phrase,
which got me to thinking of the complex center due to the pulls of
all the planets and such (e.g., the center of gravity between the Sun
and Jupiter actually lies outside the surface of the Sun). So the Sun
does a bit of a dance in its orbit around the Milky Way.

Then there is the oscillating motion of the Sun and planets in the
Orion Arm of the Galaxy. Scientists believe that the Sun travels
from one side of the Orion Arm to another as it revolves around
the Galaxy's center. Please don't ask for a reference on that one,
as i think i remember reading it in sci.astro once. Maybe true,
maybe not?

As Herc mentioned, the Solar System does revolve around what is
believed to be a black hole at the center of our Milky Way Galaxy.
The period of revolution is from 200 million to 250 million years (i
have read both figures... i think the "250 million" is the more recent
estimate).

In addition, there is the motion of the Milky Way Galaxy around the
center of the cluster called the "Local Group." This includes the
Andromeda Galaxy as well as perhaps over 30 other galaxies, most
of which are dwarf galaxies. There may be more waiting to be
discovered.

Now, the Local Group of galaxies are part of a very much larger
group named the Virgo Supercluster. So there may also be some
presently impossible to measure velocity associated with movement
of the entire Local Group around and/or through this Supercluster.

At this point, it seems that the expansion of space itself begins to
become more and more important. This is believed to have only an
immeasurably tiny effect locally.

You can see that to pick a fixed point in space and then to try and
determine the relative motion of the Sun or anything else to that
fixed point would be a monumental task. And i don't believe it's
ever been done, as at this point in our tek-level it's probably not
possible.

Nice thoughts, though. Thanks for stimulating them.

happy days and...
starry starry nights!

--
Fire... fire in the sky,
'Round we dance till dawn is nigh,
Fire... fire in the sky,
Death is so surreal!

Fire... fire in the sky,
Lovers laugh and lovers cry,
Fire... fire in the sky,
Life is how you feel!

Paine Ellsworth

separately posted to alt.astronomy and rec.org.mensa

"Muff Diver" wrote in message
:--) I always wondered, compared to a fixed point in space, what direction
:--) and at what velocity is the center of mass of the sun, the theoretical
:--) center of mass of our solar system, traveling.
:--)
:--) Any astro-whatevers out there know? Or is the planet earth just going nowhere fast.? LOL !
:--)

On Sun, 22 Jun 2003 15:01:19 +1000, "|-|erc" wrote:
:--)Cross posted to alt.astronomy, the sun orbits the center of our galaxy,

I understand the context - don't be offended -- when I ask, in jest --

"If the sun had been cross posted to alt.something.else would it orbit something
other than the center of our galaxy ? "


:--)in phase with all the surrounding stars so not like a planets orbit, something
:--)like a 2 million year period if memory serves.

And our galaxy is in motion.
Mapping the universe as it is in a "now" sate would require taking
an arbitrary fixed point and regressing the known motion of space objects.

In the case of our solar system, one star among many in our galaxy, it would only
be practical to regress the motion of the galaxy in a long term regression of apparent motion.
Question is still "what direction, what velocity?".

Happy Solstice.

AAAAAAk..!! Accidently hit the 'send' button.
But to answer Painus' statement, there is an
approximation of our Local Group's velocity relative to a 'fixed point'
in space. And that's the cosmic microwave background radiation (CMBR)
rest frame. There is a faint but detectable Doppler shift in the CMBR
from one side of the sky to the other, called the dipole anisotropy.
This slight red-blue shift gives the direction and approximate speed of
our Local Group's drift against the background 'rest frame'. It works
out to a few hundred km/ sec. A web search under 'dipole anisotropy' and
'CMBR rest frame' would be worthwhile.
BUT this says nothing about whether the 'rest frame'
itself may be flowing from a point of origin to a point of dissolution
(like from the BB to the Big Crunch). The sphere of our visible cosmos
would be like a boat adrift on a river; in our restricted view, we see
nothing of the river's origin or the plunging waterfall up ahead.

oc

|-|erc wrote:

Cross posted to alt.astronomy, the sun orbits the center of our galaxy,
in phase with all the surrounding stars so not like a planets orbit, something
like a 2 million year period if memory serves. galaxy speeds aren't given an absolute
speed in current models, though a relative figure against neighbouring galaxies
might be considered the absolute speed.

The sun's period of revolution around the galactic centre is about
200 million years. Neighbouring galaxies aren't much use as velocity
references because they tend to have high speeds relative to our own.

--Odysseus

Muff Diver wrote:

separately posted to alt.astronomy and rec.org.mensa

Cross-posting is simpler, don't you think, keeping the thread in one piece?

[snip]

In the case of our solar system, one star
among many in our galaxy, it would only
be practical to regress the motion of the galaxy
in a long term regression of apparent motion.
Question is still "what direction, what velocity?".

I believe the princpal technique used involves averaging the apparent
space motion of a great many stars. Obviously the value obtained will
depend on the objects selected, so different surveys have arrived at
various results. According to _Burnham's Celestial Handbook_ (1978)
the "Solar Apex" lies in the general direction of the star Vega
(Alpha Lyrae), and we're heading towards it at something like 12 mps
(19 km/s). The most recent survey he cites was conducted in 1967 and
included 25,800 stars, placing the Solar Apex "very near the star 4
Cygni"; in 2000.0 coordinates this is roughly RA 19.5h, Dec +36°.

--Odysseus

We don't have a name for galactic orbits / years, would be useful since
its hard to visualise a time line when millions and billions of years
are referenced. But if we said Earth cooled after 0.3 galactic orbits,
then cellular life appeared after 1 galactic orbit, then multicellular
life appeared at 20 orbits, much easier to comprehend.

Herc


Mensa thread compiled for alt.astonomy:



Cross posted to alt.astronomy, the sun orbits the center of our galaxy,
in phase with all the surrounding stars so not like a planets orbit,
something
like a 2 million year period if memory serves. galaxy speeds aren't given an
absolute
speed in current models, though a relative figure against neighbouring
galaxies
might be considered the absolute speed.

The sun's period of revolution around the galactic centre is about
200 million years. Neighbouring galaxies aren't much use as velocity
references because they tend to have high speeds relative to our own.

--Odysseus


This period of time, a cosmic year, occurs once every 225 million years. The
Sun has orbited the galaxy more than 20 times during its 5 billion year
lifetime.

AM



This touches upon a point for which I have no firm answer. The
rotation of a galaxy represents a very large amount of kinetic
energy, in the form of angular momentum. What imparted this
angular momentum to the galaxy initially?

I have tried to reconcile this through some form of Coriolis
effect, but this falls short. It would require a spherical
universe, with a net angular momentum.

Why are galactic shapes so very similar to the shape of a
tropical storm? The storm's shape can be attributed to the
Coriolis effect.

GLR



Gordon:

Why are galactic shapes so very similar to the shape of a
tropical storm? The storm's shape can be attributed to the
Coriolis effect.

Not quite. The Coriolis effect causes rotation and determines the direction of
rotation, cw vs. ccw. If a large number of things are rotating (for whatever
cause) the shape of the conglomerate is determined by the interaction between
the parts, say isobars or gravity. A tropical storm and a galaxy are rotating
for different reasons. They take the same shape for a common reason.

This touches upon a point for which I have no firm answer. The
rotation of a galaxy represents a very large amount of kinetic
energy, in the form of angular momentum. What imparted this
angular momentum to the galaxy initially?

The big bang? Things moving through space will keep movng. It takes energy to
stop them or to alter course. That's where gravity comes in.

Doug Chandler



Thanks, Doug. I have no disagreement with what you have said, but
I still have some questions on these matters. If our universe was
initiated with the "Big Bang" from a point, and radiated outward,
it seems there would be no angular momentum involved. What is/was
the source of the angular momentum that seems evident in the
swirling galaxies?

If, on the other hand, our universe was initiated from, not a
point, but a very small, very rapidly rotating sphere (black hole
in another space/time set), this could explain the observed
angular momentum. But, this hallucination bogs down when the
questions are asked, "What was the initial sphere a part of? What
was it rotating with respect to?"

GLR


Gordon:

If our universe was
initiated with the "Big Bang" from a point, and radiated outward,
it seems there would be no angular momentum involved. What is/was
the source of the angular momentum that seems evident in the
swirling galaxies?

Just to keep it down to the basics, imagine a universe empty except for two
objects. The two objects are moving in different directions at some speed.
Eventually, when they come within range of mutual gravity, they will start
bending each other's trajectories. Voila! - angular momentum.

Now add a few trillion objects of varying mass and course and speed, and watch
the interactions. The original singularity "before" the big bang did not have
to be rotating.

And there I draw the line - about the big bang. There are too many
unanswerable questions for a sane debate. It seems almost to boil down to a
matter of faith.

"God/big bang made the universe."
"Okay, where did He/it come from?"

Doug Chandler




If our universe was
initiated with the "Big Bang" from a point, and radiated outward,
it seems there would be no angular momentum involved. What is/was
the source of the angular momentum that seems evident in the
swirling galaxies?

Play billiards. Off center collisions easily convert
linear motion into rotation.

If, on the other hand, our universe was initiated from, not a
point, but a very small, very rapidly rotating sphere (black hole
in another space/time set), this could explain the observed
angular momentum. But, this hallucination bogs down when the
questions are asked, "What was the initial sphere a part of? What
was it rotating with respect to?"

Spinning causes internal forces which do not rely on any
external comparison. But to really confound matters, the
rules inside a Schwarzchild radius aren't the same as on
the outside. For example, a black hole diameter does not
measure on the inside that which conventional math demands
based on measuring the circumference remotely from the
outside.

To complicate matters just a bit more, explosions, by their
very nature, have some unpredictable components. Getting
these to work reliably as intended was Feynman's highly
acknowledged contribution to the Manhattan project.

When you have particles coming out of an explosion some
number are probably already spinning. Consider the case
of a particle departing a chamber being subjected to subsequent
sequential additional shock waves from many different angles
in an environment where pressure is rapidly reducing (varying
subsequent the shock wave velocities) and you have an image
of a bullet being fired.

So you contain it in a barrel in order to make it behave
predictably and improve energy transfer in a repetitive
sequence while training it to fly straight.

For extra points, why do the pellets fired by a shotgun
fly in an expanding pattern? Assuming symmetric packaging
of the pellets in a shotgun shell, why are the patterns
in a target usually non symmetrical?

Bill



Several factors, of course -- deformation, inconsistent mass
distribution within the pellets, wind resistance affecting the
pellets in front & weak vacuum forces the particles behind,
minor variations in powder charges, the weapon's choke, & of
course the biggies of lack of stabilizing spin & the wadding
peeling away (thus the containment it provides being lost).

B

We don't have a name for galactic orbits / years, would be useful since
its hard to visualise a time line when millions and billions of years
are referenced. But if we said Earth cooled after 0.3 galactic orbits,
then cellular life appeared after 1 galactic orbit, then multicellular
life appeared at 20 orbits, much easier to comprehend.



and dinasaurs lived for the last 2 orbits up to 1/3 orbit ago. much easier
than the lack of understanding of the past everyone has now miixing
millions and billions and 10 thousands and 100 thousands and 100 millions everywhere.


name for galactic years...... month is a moon orbit, year is a earth orbit, ? is a sun orbit
.......a sunth?

Herc