Editing Galaxy morphological classification (section)

===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).<ref>{{Cite web|url=https://ned.ipac.caltech.edu/level5/Tinsley/Tinsley1.html|title=Qualitative and Quantitative Classifications of Galaxies|website=ned.ipac.caltech.edu|access-date=2019-02-06}}</ref> 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<sub>B</sub>/M<sub>T</sub>) and the Hubble stage is M<sub>B</sub>/M<sub>T</sub>=(10−T)<sup>2</sup>/256 based on local galaxies.<ref>{{Cite journal|title=Simulation of the Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies|journal = The Astrophysical Journal|volume = 698|issue = 2|at=Equation (18)|arxiv = 0904.2221|doi = 10.1088/0004-637X/698/2/1467|year = 2009|last1 = Obreschkow|first1 = D.|last2 = Croton|first2 = D.|last3 = De Lucia|first3 = G.|last4 = Khochfar|first4 = S.|last5 = Rawlings|first5 = S.|bibcode = 2009ApJ...698.1467O| s2cid=204925243 }}</ref>

Elliptical galaxies are divided into three 'stages': compact ellipticals (cE), normal ellipticals (E) and late types (E<sup>+</sup>). Lenticulars are similarly subdivided into early (S<sup>−</sup>), intermediate (S<sup>0</sup>) and late (S<sup>+</sup>) types. Irregular galaxies can be of type magellanic irregulars (''T'' = 10) or 'compact' (''T'' = 11).

{| class="wikitable" style="text-align: center; margin: 1em auto;"
|+ Numerical Hubble stage
!Hubble stage ''T''
| −6
| −5
| −4
| −3
| −2
| −1
| 0
| 1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
| 9
|9-10
| 10
| 11
|12
|13
|-
!de Vaucouleurs class<ref name="deVaucouleurs1994"/>
| cE
| E
| E<sup>+</sup>
| S0<sup>−</sup>
| S0<sup>0</sup>
| S0<sup>+</sup>
| S0/a
| Sa
| Sab
| Sb
| Sbc
| Sc
| Scd
| Sd
| Sdm
| Sm
|Ir
| Im
| Irp
|d Trans
|dSph
|-
!approximate Hubble class<ref>{{cite book |last=Binney |first=J. |author2=Merrifield, M. |title=Galactic Astronomy |date=1998 |publisher=Princeton University Press |location=Princeton |isbn=978-0-691-02565-0}}</ref>
| colspan="3" align="center" | E
| colspan="3" align="center" | S0
| S0/a
| Sa
| Sa-b
| Sb
| Sb-c
| colspan="3" align="center" | Sc
| Sc-Irr
| colspan="3" align="center" | Irr I
|Irr Il
|d E
|dSph
|-
|}
The use of numerical stages allows for more [[Quantitative research|quantitative]] studies of galaxy morphology.