Hi All,

 There is a new piece of software out there waiting for your tests.
It’s ORSA, which allows you to make many different kind of simulations
in the real Solar System or in a totally-simulated universe. All the
operations are performed using a comfortable, coherent and well
designed graphical user interface.

 Download it here: http://orsa.sourceforge.net/download.html

 Both source code and a static binary are available, so if you are too
busy to compile the whole thing, get the binary and start.

 Hope you like it! Feedback will be appreciated, possibly using the
forums or the mailing list on the ORSA website.

 Thanks.

 –Pasquale

I know that a rigid body’s rotational inertia increases as its density
decreases (for example, if I stretch my arms out while whirling on a
swivel chair, I spin slower).  Does this effect occur when an artificial
satellite launches into orbit and thereby spreads out the rotating
terrestrial mass?

A satellite does not have much mass compared to the planet’s mass, but we
are mathematicians, so we know that we will eventually have to cope with
the problem of "limit of rotational inertia as satellite mass approaches
planetary mass."

hallo!

As part of my semester thesis at the Institute of Theoretical Physics
(I am computer science student at ETH Zuerich) I wrote a visualization
tool for TIPSY files on Linux.

The program can run on one or many processors (using the MPI library)
and can be found at http://hubble.sourceforge.net
The rotation of the model was done using an exercise from the graphics
course.
The feature I am most proud is that by right clicking with the mouse,
the model centers in x, y and z direction, where z is the coordinate
of the particle with maximum density.
The program features 10 color maps, an edge detection filter and three
plot modes: maximum density, nearest particle and estimation along
line of sight (the last one is used if the densities are missing).
The "projection and clipping" step can be optimized for AMD or Intel
architectures.

I’d like to know if it is already usable, or if I should put
additional
effort on it (although I am a little bit tired of it).
thank you for your comments (and maybe help, it’s Open Source

Tiziano Mengotti

http://neo.jpl.nasa.gov/risk/2003qo104.html

I ain’t gonna make any big deal about this 2.4 km asteroid having a
couple of Torino Scale 1′s on its risk table.

But,
here is my question, there are more than 20 passes inside the Moons
orbit, I am guessing from the sigma impact distances and ‘width’ that
would still hold , with further computations. Should make for some
interesting radar observations. Optical too. Maybe a manned
expedition!

Kind of wish JPL would do an non-two body , geocentric animation of
this one.

My question may seem like a newbie’s question, but I am now very confused.
I do not understand why the period of the precession is given to be around
26000 years. Consider this:

The annual precession was given by Bessel to be
    50".2235 + t*0.0002443610 where t is the number of years since 1800
    (Connaissance des temps for 1831)

I know that current formulas are a bit different, but this is just to set
the context, and the conclusion will be the same.

The previous formula gives a precession period of about 25800 years,
when only the constant term is taken into account. But take
the second term into account, and you find a precession period of about
24360 years.

Here, I have of course assumed that the formula stays valid for that
period, and I have also ignored quadratic terms.

Assuming the formula given above is still valid, after 24360 years
another shorter period will start, and so on.

But the problem is there.
Why does everybody keep writing of a 26000 years period, when there
doesn’t seem to be such a thing?

Thanks.

Denis Roegel

I am trying to understand what was the knowledge of the precession
of the equinoxes in 1840, and this leads me to search the theory
of Earth’s obliquity. I need to find out when it was discovered that
the obliquity oscillates, and not merely decreases (as it currently
does). For instance, the Connaissance des temps around 1840 only tells
about a decrease of 48" by century. No oscillation is mentioned.
Was it because the oscillation theory was not known? And if it was
known, who was the first to publish it and where?

Thank you very much for your help,

Denis Roegel
assistant professor in computing science
Nancy, France

Dear Colleagues,

Vol 12 No 6 of the International Journal of Modern Physics D (IJMPD)
is out. Articles are available in electronic format at
http://www.worldscinet.com/ijmpd.html

Table-of-contents:

A Word from the Managing Editors

Review

Entropic Issues in Contemporary Cosmology
by D. H. Coule

Research Papers

Mixmaster Chaoticity as Semiclassical Limit of the Canonical Quantum
Dynamics
by Giovanni Imponente and Giovanni Montani

Cosmological Predictions from the Misner Brane
by Pedro F. Gonzalez-Dmaz

Spherically Symmetric Space Time with Regular de Sitter Center
by Irina Dymnikova

A Generalized Vacuole Model in Higher Dimensions
by A. Banerjee and S. Chatterjee

Neutrino Asymmetry in General Relativistic Rotating Radiative Stars
by L. C. Garcia de Andrade

FLRW Universes from "Wave-Like" Cosmologies in 5D
by J. Ponce de Leon

Investigations of Pulsational Properties and Evolution of Propagation
Diagram in Some δ Scuti Star Models
by N. Kiziloğlu, H. Kirbiyik and R. Civelek

Entropy of a Rotating and Arbitrarily Accelerating Black Hole
by Xuejun Yang, Yiwen Han and Zheng Zhao

Trapping Photons by a Line Singularity
by Metin Arik and Ozgur Delice

Perfect Fluid Cosmological Models with Time-Varying Constants
by Josi Antonio Belinchsn and Indrajit Chakrabarty

Radiating Gravitational Collapse with Shear Revisited
by R. Chan

Sincerely,
The Editorial Board
IJMPD

Thought the list might be interested in the following item …

Mars hotspots may be best sites for life

Giant ice towers that formed next to steaming volcanic vents in the
freezing atmosphere of Mars may be the best place to look for life on
the red planet, Australian research suggests.

http://www.abc.net.au/science/news/stories/s917757.htm

I think it is pretty well-known by now that DeSitter space can be
sliced in lots of different ways, eg by flat slices or by
spherical ones. What I don’t understand is this: why does
anyone take the flat slicing seriously? I mean, it is obviously
going to lead to a geodesically incomplete spacetime—you can
have timelike worldlines coming in from "beyond the universe"!
That is pretty ridiculous—if you are going to let me do that,
I can declare that the world-tube of George Bush is a
"spacetime", simply by cutting away the rest of the universe.
When George eats a pretzel, that pretzel comes from beyond
the Georgiverse—but if that is ok for DeSitter, it should be
ok for George.

We don’t normally do that kind of thing; geodesic
incompleteness is tolerated only when the curvature diverges or
something like that. So why should we tolerate it in the
case of DeSitter space? The only special thing there is that,
being empty of matter, DeSitter is extremely symmetric, so
you can hide the incompleteness with a nice choice of
coordinates. This is just like the Milne Universe, a
so-called cosmology which is really just a chunk of
Minkowski space. The fact is, however, that the full DeSitter
has spheres as slices; the flat slicing is just a
mathematical trick of no real importance, obtained by
cutting away half of the Penrose diagram, and hence just
like the George Bush Universe constructed above.
In short, DeSitter is REALLY a cosmology with finite
spherical space.
Right?

This is a test posting.  You can/should ignore it unless you’re one
of the s.a.r moderators.

–
— "Jonathan Thornburg (remove -animal to reply)" <jth…@aei.mpg-zebra.de>
   Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
   Golm, Germany, "Old Europe"     http://www.aei.mpg.de/~jthorn/home.html      
   "Washing one’s hands of the conflict between the powerful and the
    powerless means to side with the powerful, not to be neutral."