Quoting ZombiesRus5, reply 32Well, I was more speaking to Galactica which some suggest being its own class as well as being Jupiter or Columbia class.
When I was trying to figure out the same naming problem, the closest thing I found to a consensus about the issue online is that the Galactica-class and Columbia-class were two different but very similar classes. Apparently the Columbia as seen in Razor is slightly bigger than the Galactica and has more armor plating or something along those lines.[/quote]
What I got from the various screen caps of the Razor flashback, the Columbia is basically a newer version of the Galactica class. I've also seen Galactica referred to as a Columbia-class battlestar in some places. Adding to the confusion is the fact that there was more than one Columbia in the series: the one destroyed in the first Cylon war (Razor) and the one destroyed in the second Cylon war (Miniseries). Here's the best picture I could find of the Columbia destroyed in the first Cylon war: http://en.battlestarwiki.org/wiki/File:Col1.jpg
This implies that Galactica is older than even the first Columbia, giving more weight to the Galactica being a Galactica-class battlestar and the Columbia-class being a refit of the Galactica-class with more armor, a larger size, and more advanced systems.
The general consensus is that the Pegasus is in fact a Mercury-class battlestar. Valkyrie-class is officially named and correct for that type.