Galaxy morphological classification
Numerical Hubble stage

De Vaucouleurs also assigned numerical values to each class of galaxy in his scheme. Values of the numerical Hubble stage T run from −6 to +10, with negative numbers corresponding to early-type galaxies (ellipticals and lenticulars) and positive numbers to late types (spirals and irregulars). Thus, as a rough rule, lower values of T correspond to a larger fraction of the stellar mass contained in a spheroid/bulge relative to the disk. The approximate mapping between the spheroid-to-total stellar mass ratio (M /M) and the Hubble stage is M /M =(10−T) /256 based on local galaxies.

Elliptical galaxies are divided into three 'stages': compact ellipticals (cE), normal ellipticals (E) and late types (E). Lenticulars are similarly subdivided into early (S), intermediate (S) and late (S) types. Irregular galaxies can be of type magellanic irregulars (T = 10) or 'compact' (T = 11).

The use of numerical stages allows for more quantitative studies of galaxy morphology.
keywords:existence, oulipo:avoid_letter[o]