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Gérard de Vaucouleurs' Atlas of Galaxy Types
Gérard de Vaucouleurs developed an extension of the Hubble classification of galaxy types involving a "three-dimensional" classification grid extending from ellipticals at one end to irregulars at the other. For elliptical galaxies, de Vaucouleurs' classifications are mostly similar to Hubble's classifications, but for other galaxies distinctions are made between normal and ringed, barred and unbarred, and transitional types, and even the simpler structures have various subclassifications, leading to a more detailed "shorthand" description. Various methods are commonly used to illustrate the system. One is a diagram of the three-dimensional grid, showing artistic impressions of the appearance of various galaxies (examples shown below). Another method is the publication of an online catalog (The Galaxy Morphology Website) showing several hundred photographs of actual galaxies as examples of specific types (the website includes all the examples used by de Vaucouleurs, as published in The de Vaucouleurs Atlas of Galaxies by Ronald J. Buta, Harold G. Corwin, Jr.* and Stephen C. Odewahn (Cambridge University Press, 2007) and numerous supplementary examples.
One thing that should be noted is that when a galaxy has a pair of characteristics (e.g., an internal ring and a spiral structure), if one of them is more prominent than the other it is shown by an underline, as in (rs), which would indicate a more prominent internal ring and a less prominent spiral structure, or (bc), meaning that the galaxy is closer to type b than to type c, or in S(AB), which would indicate a spiral galaxy with a more prominent bar (B) than not (A), but still somewhere between a barred and un-barred spiral galaxy. Similarly, the prefix (R) indicates an external ring, (RR) a double external ring, and (R') a partial external ring (this means that things can get pretty complicated, but that a detailed "galaxy type" may tell the informed reader a lot more about the appearance of the galaxy than the original obvious but simpler Hubble classifications).
When complete this page will include thumbnail images of every galaxy in The Galaxy Morphology Website (said images linked to the corresponding image page in the de Vaucouleurs Atlas of Galaxies Image Database or New Images not in the printed Atlas), and the NGC/IC/PGC designation of each galaxy (said designations linked to their entry on my website).
Note: The obvious order for the table/images below would be according to the galaxy classification; but some galaxies defy simple classification, and for that and presumably other reasons the order of the plates in de Vaucouleurs' Atlas is not strictly in order of the classification. But rather than second-guess him and those who have updated and expanded on his original work I have temporarily left most of the images in the order presented on the external site. However, when I have finally created a link to every image page in the Galaxy Morphology Website, I will try to organize the order of the links and images so that they form as smooth a transition from type to type as possible.
*Credit Where Credit Is Due: A number of references to the de Vaucouleurs Atlas in the individual entries in my NGC/IC Catalog refer to Dr. Corwin's help in clearing up apparent inconsistencies; those are due both to his original work in producing the 2007 edition of the Atlas, and to the fact that he and his website have been invaluable aids in my effort to complete my Catalog.
Examples of the de Vaucouleurs classification scheme
Above, a simplified Hubble-de Vaucouleurs classification scheme for elliptical and lenticular galaxies
Below, a similar scheme for spiral galaxies (Image Credit above & below Antonio Ciccolella / M. De Leo)
Below, a diagram showing the three-dimensional version of the basic de Vaucouleurs classification scheme
Note: The type A and B (unbarred and barred) classification does not apply to strictly elliptical galaxies
Also, in my catalog, de Vaucouleurs' type E+ is represented by E/S0, E/SA0, E/SB0, etc, as appropriate
The de Vaucouleurs Atlas of Galaxy Types and Supplementary Images
Elliptical and (Dwarf) Spheroidal Galaxies / Lenticular Galaxies
"Normal" Spiral Galaxies / Barred Spiral Galaxies / Transitional Spiral Galaxies
In designation order but not yet in type order