Astrophysics (Index)About

galaxy classification

(Hubble sequence, Hubble classification)
(morphological classification of galaxies)

The commonly-used galaxy classification indicates a galaxy's morphology (galaxy morphology), i.e., shape and overall structure, based upon its visual appearance. Edwin Hubble developed the basic classification still used, the Hubble types, known collectively as the Hubble sequence or Hubble classification (though current usage includes refinements subsequent to Hubble's work, e.g., by Allan Sandage and Gérard de Vaucouleurs):

(The term disk galaxy for a disk-like shape includes the above spiral and lenticular galaxies.) Hubble laid out the types in a Y-like diagram in the shape of a horizontal tuning fork and you do see references to the classification-structure as a tuning fork. Among the improvements over time have been suffixes and some prefixes, to specify more detail, often describing galaxies formerly classified as "irregular":

Parenthesis around suffix letters appear to be a means of distinguishing them, e.g., the parenthesis in "(s)m" makes clear that there isn't some specific meaning to the pair, "sm". Dwarf galaxies have their own terms: dE, dS, and dIrr for dwarf elliptical, spiral, and irregular, and dSph for dwarf spheroidal galaxy. Some example galaxies/types:

Another classification system is the Morgan classification, and one of its classifications, cD, is still commonly seen for central elliptical galaxies. There also exists some classification specific to radio galaxies.


(galaxies,classification)
Further reading:
https://en.wikipedia.org/wiki/Galaxy_morphological_classification
https://en.wikipedia.org/wiki/Hubble_sequence
https://www.astro.umd.edu/~richard/ASTRO620/davis_week5.pdf
https://ned.ipac.caltech.edu/level5/Sept11/Buta/Buta_contents.html
https://arxiv.org/abs/1201.6406
https://ui.adsabs.harvard.edu/abs/1926CMWCI.324....1H/abstract
https://astronomy.swin.edu.au/cosmos/H/Hubble+Classification
https://astronomy.swin.edu.au/cosmos/G/Galaxy+Types

Referenced by pages:
3C 295
3C 48
Andromeda (M31)
bar
Canis Major Dwarf Galaxy
Centaurus A
Circinus Galaxy (ESO 97-G13)
elliptical galaxy
ESO 137-001
galaxy
Gini/M20
IC 342
Large Magellanic Cloud (LMC)
lenticular galaxy (S0)
M64
M82
M87
Messier 74 (M74)
Morgan classification
morphology
N galaxy
NGC 1600
NGC 253
NGC 2770
NGC 3314
NGC 6946
NGC 7331
PCA analysis
peculiar galaxy (p)
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
Sagittarius Dwarf Irregular Galaxy (SagDIG)
Small Magellanic Cloud (SMC)
Spindle Galaxy (NGC 5866)
spiral galaxy
Triangulum Galaxy (M33)
Ursa Major II Dwarf
van den Bergh galaxy classification

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