For ease of reference, the Hubble classification scheme is often used to subdivide galaxies into two morphological 'types':
- Early-type galaxies: elliptical and S0 galaxies.
- Late-type galaxies: spiral and irregular galaxies.
Although we now know that the Hubble classification does not form an evolutionary sequence, these names are derived from this initial assumption.
A comprehensive survey of nearby galaxies reveals the following percentages for the different morphologies:
- 10% elliptical
- 20% S0 (lenticular)
- 60% spiral
- 10% irregular or peculiar
Extrapolating to the Universe as a whole, it is estimated that 70% of all galaxies are late-type galaxies and only 30% are early-type. However, this is in contrast to what is found in galaxy clusters where early-type galaxies dominate - an example of the observed morphology density relation where the dominant galaxy type varies with environment.