Re: Spitzer Image: Dying Star Goes Out With a Ring

From: Steve Willner (willner_at_cfa.harvard.edu)
Date: 08/18/04 

Date: 18 Aug 2004 17:59:11 -0400

In article <1jwSc.1638097$Ar.542016@twister01.bloor.is.net.cable.rogers.com>,
 Mad Scientist <alice@in.wonderland> writes:
> Gravity in any galactic object is strongest at the 'equator' which could
> be thought of as a disk. In our solar system, the planets rotate around
> the 'solar disk'.

The planets revolve around the Sun pretty close to a plane, if you
ignore Pluto. Comet orbits are not confined to a plane; they have
all inclinations. None of this has anything to do with gravity
allegedly being "stronger at the equator," which it isn't. (On
Earth, objects weigh _less_ at the equator than at the poles.)

> The galactic arms of any galaxy are generally spread
> out according to a 'galactic disk-like' form, depending on what time you
> see a galaxy.

Some galaxies have disks; some ("ellipticals") don't. I think the
latter account for most of the mass in galaxies. And on human
timescales, it doesn't matter "what time" you see a galaxy. They
don't change very quickly. 

-- 
Steve Willner            Phone 617-495-7123     swillner@cfa.harvard.edu
Cambridge, MA 02138 USA                 
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