APOD and General Astronomy Discussion Forum
https://asterisk.apod.com/
http://antwrp.gsfc.nasa.gov/apod/ap980110.html wrote:
Kitt Peak 2.1-meter Telescope
Credit: W. C. Keel & R. E. White III (U. Alabama, Tuscaloosa),
What can I say excepy Wow! Hubble rocks! 8)
Stephan's Quintet
Credit: NASA, ESA, and the Hubble SM4 ERO Team
Explanation: The first identified compact galaxy group, Stephan's Quintet is featured in this stunning image from the newly upgraded Hubble Space Telescope. About 300 million light-years away, only four galaxies of the group are actually locked in a cosmic dance of repeated close encounters. The odd man out is easy to spot, though. The four interacting galaxies (NGC 7319, 7318A, 7318B, and 7317) have an overall yellowish cast and tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. But the bluish galaxy at the upper left (NGC 7320) is much closer than the others. A mere 40 million light-years distant, it isn't part of the interacting group. In fact, individual stars in the foreground galaxy can be seen in the sharp Hubble image, hinting that it is much closer than the others. Stephan's Quintet lies within the boundaries of the high flying constellation Pegasus.
I think it's technology more than technique. Although both may have improved, WFC3 is obviously far superior to WFPC2. Amazing what a difference 10 years can make. Improvements in technique and software will make a greater impact on images from ACS, such as NGC 6217 or Omega Centauri.geckzilla wrote:The updgrade sure does pick up those little background galaxies a lot better. Or is it just refined technique?
It would look similar to our own sky, but there would be a more complex Milky Way sort of pattern- for instance, while we see our galaxy as a faint band with some dust lane structure, if you were surrounded by interacting galaxies you'd see several bands at different angles across the sky. If you were actually centered in an area of interaction, you might see nothing but one big band- like the Milky Way covered the entire sky- a diffuse faint glow, probably with some darker dust structure in front.billMe wrote:It would be great to see what the sky look like living on a planet on the outer edge of one of these galaxies towards the center of the interaction.
Nothing wrong with your logic. There is a very wide range of galaxy sizes, so there's nothing particularly odd about the foreground galaxy in this case happening to be smaller than the background galaxies.Sarba Guha wrote:The "Blue Galaxy" is merely 40-million light years away while the others are 300-million light years away. The difference in distance is by a factor of 7.5 - right?
YET, the Blue Galaxy doesn't appear more than 2 to 3 times larger than any of the others.
Does that mean that those galaxies are twice, or even more than thrice as large, as the Blue Galaxy?
Sarba Guha wrote:The "Blue Galaxy" is merely 40-million light years away while the others are 300-million light years away. The difference in distance is by a factor of 7.5 - right?
YET, the Blue Galaxy doesn't appear more than 2 to 3 times larger than any of the others.
Does that mean that those galaxies are twice, or even more than thrice as large, as the Blue Galaxy?
In the explanation to the image at Hubblesite.org, it calls NGC 7320 a dwarf galaxy, it's a lot smaller and a little closer than NGC 7331. Could NGC 7320 be a companion to NGC 7331?Chris Peterson wrote:Nothing wrong with your logic. There is a very wide range of galaxy sizes, so there's nothing particularly odd about the foreground galaxy in this case happening to be smaller than the background galaxies.
To be fair the Blue Galaxy (NGC 7320) is more like 4 times larger in apparent diameterSarba Guha wrote:The "Blue Galaxy" is merely 40-million light years away while the others are 300-million light years away. The difference in distance is by a factor of 7.5 - right?
YET, the Blue Galaxy doesn't appear more than 2 to 3 times larger than any of the others.
Does that mean that those galaxies are twice, or even more than thrice as large, as the Blue Galaxy?
If it does then is the small (relatively speaking) yellowish object to the bottom of the image one of the quintet or is the central object composed of two of the five as it seems to have two nucleii. 
I know that Cassini has an Ultra Violet Imaging Spectrometer (UVIS) so I thought that might be what it stands for, but a search of the Hubble site brought up mentions of an "UV/visible (UVIS) channel" on the WFC3, so I'm now confused (as usual 
).The new WFC3 instrument has two channels; one covers near UV and visible (the UVIS channel) and one covers near IR (the IR channel). So on the HST, UVIS means something different than on Cassini.DavidLeodis wrote:Apologies if I seem to be a nuisance but I have another question. In the related Hubble news release it mentions that some of the image data was acquired by the UVIS on the WFC3 (Wide Field Camera 3). Just what does that UVIS stand for. :?: I know that Cassini has an Ultra Violet Imaging Spectrometer (UVIS) so I thought that might be what it stands for, but a search of the Hubble site brought up mentions of an "UV/visible (UVIS) channel" on the WFC3, so I'm now confused (as usual :) ).
Stephan's quintet really is a quintet. Although NGC 7320, the blue foreground spiral, is not a part of the same galaxy group, there is a another galaxy, NGC 7320c, off image to the upper right about the same visual distance from NGC 7319 (top right) as NGC 7317 (bottom left) that has the same approximate red shift as the other four galaxies making it a part of the group. It may be the intruder that is causing the disruptions in NGC 7318a, 7318b and 7319. It has been said to be associated with the tidal tail seen at the top center of the APOD. The fifth galaxy can be seen in APOD 2009 August 6 - Galaxies in Pegasus directly above this grouping at the bottom left.DavidLeodis wrote:Does the image show all five of the quintet.
and a bit 
at my lack of know how. 
Stephan's Quintet: Intruder Galaxy Shocks Tightly-Knit Group wrote:The four galaxies A, B, D and E strung out diagonally across the wide field optical image are at a distance of about 280 million light years from Earth. The large-appearing galaxy F in the lower left of this image has now been identified as a foreground galaxy at a distance of about 35 million light years, leaving the group originally identified as Stephan's Quintet with only a quartet of galaxies. However, if we include galaxy C, which is at the same distance as the other four galaxies, it becomes a quintet again!
