I am curious, partly because of a test tomorrow, about the difference between peculiar and irregular galaxies. Pretty much my current understanding is that peculiar galaxies are formed from gravitational interactions between/among galaxies, and irregular galaxies are just different. From the textbook type thing that we use, it says that peculiar galaxies "have a noticeable peculiarity in addition to one of the basic shapes described above (spiral and elliptical). A galaxy might have a jet of gas sticking out, for example, or be wrapped with extra dust. These galaxies are labeled (pec) for peculiar." That's pretty much all the text has to say about that, and irregular galaxies are described as having "no special shape" and sometimes "seem to have a trace of spiral" or "are truly irregular." SO! What's the difference between having a "noticeable peculiarity" and having "no special shape"? If I was to put spiral, peculiar, and irregular galaxies on a scale of wacko-ness from 1 to 10, would it be that spirals are non-wacko 1s, peculiars fairly-wacko 5s, and irregulars are crazy-wacko 10s? Also, what is the difference in their life stages? If I am to believe that it is the peculiar galaxies that are formed from galactic collisions, how were the irregulars made? I've been looking at pics on google of peculiars and irregulars, and I might be naive or ignorant, but I'd say that the differences are subtle considering the variety of galaxy shapes that each group includes. SO SO SO, is there any steadfast definition I can cling to while I take my test and use to distinguish the two?? Really that's my problem, being able to distinguish the two. Also I think that google may be giving me results that are not exclusively peculiar or irregular, so that may be messing stuff up. Thanks for any help you can offer!