62 million year extinction cycle

In article ,
Allan Adler wrote:

(Paul Schlyter) writes:

So, as regards perpendicular motion, it's kind of like someone drilled a
hole through the Earth and dropped a ball into the hole. Is there any force
that tends to attenuate the bounces? If so, when might we expect the ball
to stop bouncing?

In the case of a ball falling through a hole drilled through the Earth:
the friction against the air would soon stop the ball bouncing - it wouldn't
even bounce once --- at least not very far. Even a human falling through air
in our atmosphere will soon reach an equilibrium speed where the air
resistance equals his weight - that equilibrium speed is approximately
200 km/h.

I'm sorry, I expressed that very badly again. Having made the analogy between
the Sun and the ball, all subsequent statements and questions about "the ball"
actually were meant to refer to the Sun. In other words, is there anything
attenuating the bobbing motion of the Sun?

Not much --- friction against the interstellar medium? Should be
quite negligible. Of course we have the remote possibility of the Sun
colliding with another star - but that probability is so low that it's
99+ % probability that the Sun will never collide with a star during its
lifetime.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

In article ,
Allan Adler wrote:

"Greg Neill" writes:

A while back I did an article for The Orrery newsletter on
some of the possible orbits for stars in a galactic
gravitational potential. Some of the trajectories considered
were for high eccentricity orbits that move through a wide
swath of such a potential. These orbits can be surprisingly
complex in form.

If interested, the issue of The Orrery with this article is
available on line as 'Sample Issue #37' (PDF file) at

http://members.allstream.net/~gneill/orrery.html

The article begins on page 9. There's a bunch of mathematical
development and a simulation program (in BASIC) to explore
some of these orbits. Plots of some sample trajectories are
given on page 13.

Thanks, I've downloaded it and will read it. I have GWBASIC on an
old machine and I can probably run it.

Those who don't have GWBasic can download it he
http://www.geocities.com/KindlyRat/GWBASIC.html
http://www.geocities.com/rhinorc/gwbasic.html
http://www.xs4all.nl/~hwiegman/gwbasic.html

and a source code converter from GWBasic to QBasic can be found he
http://www.xs4all.nl/~hwiegman/qbasic.html

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

(Paul Schlyter) writes:

Those who don't have GWBasic can download it he
http://www.geocities.com/KindlyRat/GWBASIC.html
http://www.geocities.com/rhinorc/gwbasic.html
http://www.xs4all.nl/~hwiegman/gwbasic.html

and a source code converter from GWBasic to QBasic can be found he
http://www.xs4all.nl/~hwiegman/qbasic.html

Thanks, that's good to know. It is resident on the DOS partition of an
old machine of mine. I'm not sure, but I might also have downloaded it
for use with FREEDOS; at any rate, I have it installed on the FREEDOS
partition of another machine. It would be nice to be able to run such
programs under Linux without having to resort to a DOS emulator and without
having to modify programs written in GWBASIC or QBASIC, respectively, to use
them on that platform.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

On Sep 10, 8:17 am, Allan Adler wrote:
When the Sun moves in its orbit in the Milky Way, what exactly is it
orbiting around and why? What kinds of general statements can be made
about the orbits of the other stars in the Milky Way? For example, are
there some basic classifications of orbit types? If so, how typical is
the Sun's orbit?

The same questions apply as well to other galaxies.

What would be a good book or article to read on stellar orbits in galaxies?

When the Sun moves in its orbit, it bobs up and down in the equatorial plane
of the Milky Way. Why does it do that? If, for comparison, we look at the
orbit of the Earth in the solar system, is there any comparable bobbing
motion?
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

What about the 225 million year galactic cycle that's rather
impressive, to say the least.

Galaxies and the Expanding Universe / Structure of Milky Way
http://sci.esa.int/science-e/www/obj...objectid=36827

Just one of many complex though otherwise good efforts for sharing the
most accurate of 2D animations on behalf of depicting our local
stellar proper motions, that's entirely relative as to our Sol that
not worth 0.0000001% (a billionth) of what otherwise every bit as good
or better for having hosted their own locally evolved intelligent
life, especially if such human intelligence only takes at most a few
million years under the right conditions.

The Geneva-Copenhagen survey of the Solar neighbourhood, by Nordström
et al., as having been further improved by Hipparcos data:
http://www.aanda.org/index.php?optio... d=42&lang=en

This computer animated 225 million year galactic rotation or galactic
life cycle offers absolute loads of somewhat less massive stellar
cycles that are clearly of what's ongoing as much closer to our Sol,
that's specifically associated by way of that graphic blue dot
representation of our insignificant little solar system.

Though intentionally exaggerated, notice how extensive their expansion
and contraction cycle is, as for that graphic animation having
indicated as to how such stellar motions are far more interactive and
thereby entirely capable of influencing our environment, whereas so
much of that stellar activity becomes near our somewhat insignificant
solar system, so much so in that it seems somewhat impossible for the
likes of Sirius not to have become closely interrelated with us.
- Brad Guth -

In article ,
Allan Adler wrote:

(Paul Schlyter) writes:

Those who don't have GWBasic can download it he
http://www.geocities.com/KindlyRat/GWBASIC.html
http://www.geocities.com/rhinorc/gwbasic.html
http://www.xs4all.nl/~hwiegman/gwbasic.html

and a source code converter from GWBasic to QBasic can be found he
http://www.xs4all.nl/~hwiegman/qbasic.html

Thanks, that's good to know. It is resident on the DOS partition of an
old machine of mine. I'm not sure, but I might also have downloaded it
for use with FREEDOS; at any rate, I have it installed on the FREEDOS
partition of another machine. It would be nice to be able to run such
programs under Linux without having to resort to a DOS emulator and without
having to modify programs written in GWBASIC or QBASIC, respectively, to use
them on that platform.

Perhaps SmallBasic could fill that need? Check it out at:

http://smallbasic.sourceforge.net/

Other free Basic compilers and interpreters, some of them multiplatform, can be
found at:

http://www.thefreecountry.com/compilers/basic.shtml

They're probably useful for running e.g. those old BASIC programs published in
Sky and Telescope many years ago.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

(Paul Schlyter) writes:
Allan Adler writes:
Thanks, that's good to know. It is resident on the DOS partition of an
old machine of mine. I'm not sure, but I might also have downloaded it
for use with FREEDOS; at any rate, I have it installed on the FREEDOS
partition of another machine. It would be nice to be able to run such
programs under Linux without having to resort to a DOS emulator and without
having to modify programs written in GWBASIC or QBASIC, respectively, to use
them on that platform.

Perhaps SmallBasic could fill that need? Check it out at:
http://smallbasic.sourceforge.net/
Other free Basic compilers and interpreters, some of them multiplatform,
can be found at:
http://www.thefreecountry.com/compilers/basic.shtml
They're probably useful for running e.g. those old BASIC programs published in
Sky and Telescope many years ago.

I looked at several Linux versions of basic some time ago. The nontrivial
condition is that there be a painless way of translating GWBASIC programs
into whatever version of basic one is considering using. I haven't seen
one that meets that condition and runs under Linux. At the very least,
the graphics commands and the commands to place text at particular places
tend to be problematic.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

On Sep 10, 8:17 am, Allan Adler wrote:
When the Sun moves in its orbit in the Milky Way, what exactly is it
orbiting around and why? What kinds of general statements can be made
about the orbits of the other stars in the Milky Way? For example, are
there some basic classifications of orbit types? If so, how typical is
the Sun's orbit?

The same questions apply as well to other galaxies.

What would be a good book or article to read on stellar orbits in galaxies?

When the Sun moves in its orbit, it bobs up and down in the equatorial plane
of the Milky Way. Why does it do that? If, for comparison, we look at the
orbit of the Earth in the solar system, is there any comparable bobbing
motion?

Besides those bobbing ups and downs, there are in fact nearby stellar
orbits and/or interactions within galaxies, not to mention whatever
rogue stars, planets or proto-moons to accommodate.

Perhaps we need to forget about all the other intelligent life within
this vast and deeply complex universe that's supposedly going away
from us faster than we can possibly keep up with, much less overtake.
Even within the local realm of our vast Milky Way galaxy is simply of
what's for the most part too far away and moving further away at too
fast of velocity as to bother with, as that's supposedly how it works
if you don't happen to believe in the best available science of
stellar proper motions, such as having that pesky 225 million year
cycle that keeps bringing all sorts of cosmic stuff together.

Galaxies and the Expanding Universe / Structure of Milky Way
http://sci.esa.int/science-e/www/obj...objectid=36827
Just one of many complex though otherwise good efforts for sharing the
most accurate of 2D animations on behalf of depicting our local
stellar proper motions, that's entirely relative as to our Sol that
not worth 0.0000001% (a billionth) of what's otherwise every bit as
good or better for having hosted their own locally evolved intelligent
life, getting especially interesting if such evolution of human
intelligence only takes at most a few million years under the right
conditions, as that's hardly anything in cosmic time.

The Geneva-Copenhagen survey of the Solar neighbourhood, by Nordström
et al., as having been further improved by Hipparcos data:
http://www.aanda.org/index.php?optio... d=42&lang=en

This computer animated 225 million year galactic rotation or galactic
life cycle simulation offers absolute loads of those internal and
somewhat less massive stellar cycles that are clearly of what's
ongoing and close enough to our Sol to matter, as specifically
associated by way of that graphic blue dot representation of our
insignificant little solar system.

Though intentionally computer exaggerated, notice how extensive their
expansion and contraction cycle is, as well as for that graphic
animation having indicated as to how such local stellar motions are
far more interactive and thereby entirely capable of having influenced
our environment, whereas so much of that stellar activity becomes
nearby to our somewhat insignificant solar system, so much so in that
it seems somewhat unlikely for the greater worth of the all-inclusive
Sirius star system not to have become closely interrelated with having
affected us.

Perhaps there's a little less doubt we're unavoidably associated with
Sirius (getting as close as 0.086 ly), and at such mutual encounters
whereas each becomes capable of exchanging a few Oort cloud icy and
perhaps a touch worth of salty items, and/or exchanging a few physical
blows from within our respective Oort clouds of somewhat substantial
debris (especially from the robust Sirius side of this highly
illuminating and interactive Oort zone gauntlet).

More than a few interesting sets of new and improved stellar 3D maps:
The Universe within 12.5 and 20 Light Years
http://www.atlasoftheuniverse.com/12lys.html
http://www.atlasoftheuniverse.com/20lys.html
- Brad Guth -

In article ,
Allan Adler wrote:

(Paul Schlyter) writes:
Allan Adler writes:
Thanks, that's good to know. It is resident on the DOS partition of an
old machine of mine. I'm not sure, but I might also have downloaded it
for use with FREEDOS; at any rate, I have it installed on the FREEDOS
partition of another machine. It would be nice to be able to run such
programs under Linux without having to resort to a DOS emulator and without
having to modify programs written in GWBASIC or QBASIC, respectively, to use
them on that platform.

Perhaps SmallBasic could fill that need? Check it out at:
http://smallbasic.sourceforge.net/
Other free Basic compilers and interpreters, some of them multiplatform,
can be found at:
http://www.thefreecountry.com/compilers/basic.shtml
They're probably useful for running e.g. those old BASIC programs published in
Sky and Telescope many years ago.

I looked at several Linux versions of basic some time ago. The nontrivial
condition is that there be a painless way of translating GWBASIC programs
into whatever version of basic one is considering using. I haven't seen
one that meets that condition and runs under Linux. At the very least,
the graphics commands and the commands to place text at particular places
tend to be problematic.

OK, if you want 100% GWBasic compatibility on Linux, including all the
obscure parts of that implementation, you'd better run a DOS emulator
on Linux. Or perhaps Wine?

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

In article .com,
BradGuth wrote:

Even within the local realm of our vast Milky Way galaxy is simply of
what's for the most part too far away and moving further away at too
fast of velocity as to bother with,

Huh?

Our galaxy isn't internally expanding with the rest of the universe
but remains at approximately the same size. So the objects in our
Milky Way galaxy are approaching us just as often as they recede from
us. The approaching objects won't approach us all the way until they
collide with us, of course, but for now and for many years to come,
they are approaching us.

And some of the galaxies on our local group are approaching us too - for
instance M31, the Andromeda galaxy, which eventually will collide with us
in the very far future. But a "collision" of two galaxies is more
like e.g. two swarms of bees passing through one another.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

In sci.astro message , Mon, 10 Sep
2007 20:59:01, Allan Adler posted:
(Paul Schlyter) writes:

and why?

Gravity of course!! What did you think?

I guess I didn't ask that very well. Of course it orbits the center of
mass of the inner stars and does so because of gravity. The same could
be said about the Earth with respect to everything closer to the Sun than
the Earth. The most important such thing is the Sun itself and it stands
out as more of a reason that the inner planets. Our Milky Way has at least
one black hole at its galactic center, so its significance, e.g., might be
compared with that of the other inner stars.

Be careful.

The usual proof that a body orbits around the centre of mass of a system
applies only to systems that are everywhere spherically symmetrical,
including ay greater distances from the centre.

No doubt there are some less-symmetrical systems in which at least some
bodies do orbit the centre of mass; but ISTM that in most cases that
will hold at best inexactly.

Granted, in the cases in question the errors are not great.


The period of ANY circular orbit is inversely proportional to the square
root of the average density within the minimum circumscribing sphere
(assuming sufficient symmetry).

--
(c) John Stockton, Surrey, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.