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5. Selected Illustrations of Galaxy Types

Classification on the Hubble-de Vaucouleurs system depends on subjective criteria; nevertheless, it works in practice, as evidenced by the fact that all classifiers are able to reproduce it well in the mean. Learning the system is best done by comparing photographs (such as those in de Vaucouleurs 1959a; the Hubble Atlas [Sandage 1961]; the Cape photographic Atlas [Evans 1957]; Morgan 1958; Sersic 1968; and in other more scattered references) with several standard classification catalogs such as Humason, Mayall, and Sandage (1956 [HMS]), Morgan (1958, 1959), van den Bergh (1960c), de Vaucouleurs (1963b), the Hubble Atlas, and the Reference Catalogue (de Vaucouleurs and de Vaucouleurs 1964) decoded by its tables 1b, 2, 3, 4, and 5.

To reproduce all type-examples here would be an unwarranted duplication of material already in the literature, but a minimal selection is given in plates 1 - 8. The photographs are chosen to show progressive variation of the three classification criteria (and their conflict in some cases), and to illustrate the continuity of arm characteristics for the massive and the filamentary types - a continuity which can be traced throughout the sequence from Sa to Sc+ for each strain separately.