I think to be consistent with WCS naming, we should call this `axis_type_names`, since it gets it's values from `CTYPE`, not `CNAME` [1] (which are defined as coordinate axis names, though usually not present).

[1] http://docs.astropy.org/en/stable/api/astropy.wcs.Wcsprm.html#astropy.wcs.Wcsprm.cname

I also worry about the potential confusion this method may cause.  If the intent is that the user will look at these names to find out which one is `RA` and `DEC`, that will be incomplete, since ra could be represented as `RA` or `GLON`.  Better to use the `lat` and `lon` members.