# Astronomy AnswersUniverse Family Tree: Galaxy

  ┌── Molecular Cloud Type :  Galaxy Cluster ─── Galaxy ──┼── Star Cluster  :   └── Interstellar Medium Spiral Galaxy Elliptical Galaxy Barred Spiral Galaxy Lenticular Galaxy Irregular Galaxy Quasar BL-Lac Galaxy Radio Galaxy Seyfert Galaxy N Galaxy Size :  5 Mpc ─── 50 kpc ───── 5 pc Earth :  Local Group ─── the Galaxy ───── (none)

A galaxy is a large collection of stars, gaseous clouds, and interstellar medium that are all bound together by gravity and that is separated from other galaxies by vast expanses of virtually starless space.

Galaxies come in different kinds. The classification scheme used most often today is due to Edwin Hubble (of Hubble-constant fame). In Hubble's scheme, there are four major galaxy classes which may each be subdivided. The major galaxy classes are:

• S = spiral galaxies
• E = elliptical galaxies
• SB = barred spiral galaxies
• Irr = irregular galaxies

In addition to this classification scheme that is based on visual appearance, galaxies are also classified based on how they behave at other wavelengths:

Our own galaxy is a spiral galaxy, probably of type Sb or Sc.

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Last updated: 2016-02-07