Measuring sun's true direction

But is it truely the spiral arm that is winding up? I speak under correction but I have it somewhere in my head that the 'arms' does not necessarily correspond to areas where stars are concentrated. Rather it is 'light' areas where less dust and gasses are? The stars just 'wanders' through these arms from time to time.

The layman
Rudolf

TVF<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote> It also would help solve the great "wind-up" mystery about spiral arms in galaxies. <hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
This one look very wind-up!
<img src=" heritage.stsci.edu/2002/07/ngc2787/0207b.jpg " border=0>

So how does the arm keep its shape instead of winding around the galaxy dozens of times? -|Tom|-

it may be that the arm you see now is not the same arm you've seen before. It may be that material keeps thrown away from the center to from arms constantly and at the same time material ejected material joints other galaxies. If your model of gravity decreasing fast is true then there is little force to keep the material in the arms attached to the center but arms keep forming.

Any observational evidence about this? I gather Tom is mhcu more fascinated by galaxy formation and rotation than of the other issues discussed here.

Remember I'm a total idiot. I fix cars.

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>[Rudolf]: But is it truely the spiral arm that is winding up? I speak under correction but I have it somewhere in my head that the 'arms' does not necessarily correspond to areas where stars are concentrated. Rather it is 'light' areas where less dust and gasses are? The stars just 'wanders' through these arms from time to time.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

The standard explanation for spiral arms is tha they are "density waves". There are really more stars in the arms -- it's not just a visibility problem. We can measure the amount of light absorption from the spectrum, and it is not significantly greater in the arms. But supposedly, extra gas and dust gravitationally delay stars as they go through arms. But then how does the gas and dust manage to stay in arms and not wind up?

There are no explanations for arms yet to which someone has not raised an objection. -|Tom|-

How many arms are observed in galaxies? And is the current system of sorting galaxies by type of any help in understanding the structure?

what is the closest we can send hubble near another galaxy, are we still discovering our own arms? If we can also get hubble out of our galactial arms then we can discover if dark matter is for real or not
[ www.astro.queensu.ca/~dursi/dm-tutorial/dm1.html ]

The intuitive mind