In message <Pine.LNX.firstname.lastname@example.org>, Kwok Man Hui <email@example.com> writes >On Tue, 27 Dec 2005, Jonathan Silverlight wrote: >> >> Why should it be any less clear than the other distant galaxies in the >> picture? It's just a background object that happens to be in line of sight, >> and inside the ring. > >Hubble moves around the Earth, which orbits the Sun. So Hubble can take >pictures at different time and can detect any abberation. Then it may >eliminate this kind of parallel background light. You may further argue >that the Earth movement compares with the distance from the background >object we observed is very small. So Hubble may not be able to distinguish >any abberation. If that is the case, I think we need an expert on this >matter. I'm no expert, but you have _got_ to be joking :-) Have you tried calculating the parallax of an extragalactic object? > >Second, I know the astronomists can filter some background light if >the source is far enough away from, say, the Hoag's object. > >> And are you sure we are seeing it exactly head-on? People thought we were >> seeing Ring Nebula in Lyra head-on, but that's not so. >> > >The commentary from >http://hubblesite.org/newscenter/newsdesk/archive/releases/2002/21/image/a > >says, > >"A nearly perfect ring of hot, blue stars pinwheels about the yellow >nucleus of an unusual galaxy known as Hoag's Object. This image from >NASA's Hubble Space Telescope captures a face-on view of the galaxy's ring >of stars, revealing more detail than any existing photo of this object. >The image may help astronomers unravel clues on how such strange objects >form." > >A "face-on" view or a "head-on" view is up to your choice of word. This >picture was taken on July 9, 2001. May be they should take a second >picture now. I have the impression that you have no idea of the distances involved here. It would take thousands of years to see a change. > >>> >>> >>> 2.) About "Ring Around a Galaxy", the vertical bluish ring is warped and >>> does not lie in one plane according to the accompanying commentary. The >>> lower clump should have more young stars. It is hardly as symmetrical as >>> the one we saw. The Haog's ring is more evenly bluish and has shown a >>> slight clockwise spiral roatation. Is it easy to get such a higher level >>> of plane symmetry by colliding two galaxies? I doubt it. >> >> Don't simulations show exactly that sort of ring? >> > >Are the two colliding galaxies having exact plane symmetry? No way you can >get such perfect galaxies. Again, why not? Don't forget that this object has aroused interest because of its symmetry. Without doing a survey of a lot of galaxies you can't even say if it's unusual. If you want a less symmetric example, consider AM 0644-741, which has already been mentioned here. > >>> Look at the polar ring shown, let me emphasize again about the commentary: >>> "The polar ring appears to be highly distorted. No regular spiral pattern >>> stands out in the main part of the ring, and the presence of young stars >>> below the ring is warped and does not lie in one plane" from the side view. >>> So the head-on view should be as symmetrical as the Haog's ring we saw. >>> >>> Not so easy to explain the Haog's object. >>> >>>> >>>> Here's another ring galaxy, called AM 0644-741: >>>> >>>> 19) The lure of the rings, Hubblesite News Archive, April 22, 2004, >>>> http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/15/image/a >>>> >>>> It's the result of a collision involving a galaxy that's not in this >>>> picture. So, maybe Hoag's object is just a specially pretty case of >>>> a galaxy collision! >>>> >>> Still doesn't explain "The weirdest thing is that inside the ring, in the >>> upper right, you can see *another* ring galaxy in the distance!" >>> I think it is quite hard to form a ring galaxy within another ring galaxy. >>> >> >> But why should it be "within" the closer galaxy? >> >> > >OK. Collide two galaxies and form two ring galaxies nearby or one within >another if the smaller galaxy is not engulfed at all. Try 1000 simulations >and see how many results fall in this scenario. Don't just argue for >argument sake. I hope you get my point. You don't get _my_ point, which George Dishman has made more clearly. The small ring has nothing to do with the big ring. It's much further away.