Stephan's Quintet was seen as five galaxies in the ninetheenth century by Stephan, but in the modern view it is one very removed galaxy superimposed on three other galaxies. The three are interacting, and a debris cloud from the interaction has become a star forming region, and looks like a fifth galaxy.

Do a Google search to easily find more information about this famous grouping. I thought the Sky and Telescope article from about a year ago was really clear.

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Forming opinions as we speak