In the normal course of observing the sky with telescopes, we expect to see galaxies near to each other in groups. When we measure the displacement of the absorption and emission lines in their spectra, we expect to find the redshifts of these galaxies to be very close, differing by only a few hundred kilometers per second (km s−1).

When we do see a much larger redshift, we instinctively feel that it is an unrelated object at a much greater distance in the far background where the expansion velocity of the universe is carrying it away from us more rapidly. It is an enormous shock therefore when we measure two galaxies that are interacting, or connected together, and find that they have vastly different redshifts.

That is what happened when I measured the redshifts of the two galaxies pictured in Figure 6-1. It was 1970 and Palomar observers still had to ride all night in the cage of the 200-inch telescope in order to obtain direct photographs and spectra of astronomical objects. An observer was usually lucky to get two spectra in a night of objects as faint as the ones in Figure 6-1. But I was following up interesting objects from my Atlas of Peculiar Galaxies, and I was interested in that class of objects where companion galaxies were found on the end of spiral arms. As in the case of the quasars, this study led to big trouble when I discovered the redshifts of the two connected objects differed by Δz = 8,300 km s−1.