Last year at Kelling I had some problems with my 'scope, and although NGC 7331 was easy, Stephan's Quintet
Stephan's Quintet provides a rare opportunity to observe a galaxy group in the process of evolving from an X-ray faint system dominated by spiral galaxies to a more developed system dominated by elliptical galaxies and bright X-ray emission.
Stephan's Quintet shows an additional sign of complex interactions in the past, notably the long tails visible in the optical image.
The brightest and largest member of Stephan's Quintet, NGC 7320, is a foreground object that isn't a true member of the Hickson association.
A trail blaze on the path to Stephan's Quintet, NGC 7331 also anchors its own galaxy grouping.
Most astronomers place NGC 7320 at roughly the same distance as NGC 7331, whereas the remaining galaxies of Stephan's Quintet
are thought to inhabit the same region as the more distant Flea trio.
Stephan's Quintet is one of 100 groups in a catalog compiled in 1982 by Paul Hickson (University of British Columbia).
Stephan's Quintet has been observed more extensively than any other compact group and has played a major role in our understanding of compact groups in general.
The first step in reconstructing the history of a group like Stephan's Quintet is to identify all the participants.
In 1999 our group used Hubble to search for luminous star clusters in Stephan's Quintet. Because they fade and redden as they age, such clusters can be used as cosmic clocks with which we can date the onset of star formation throughout the group.
According to its discoverers, the Stephan's Quintet
starburst is the first to be observed taking place outside of a galaxy, though indirect evidence for an extragalactic starburst in the Leo Triplet has already been documented (S&T: December 1998, page 26).
For example, when you call up a region from RealSky - say, Stephan's Quintet
in Pegasus - and then overlay the catalog positions, they don't match.