The Hubble
Classification

Galaxies may be viewed as the basic building blocks for the large-scale visible stucture of the Universe. There are may galaxy types, having rather diverse features. Therefore, it is useful to have a way to classify galaxies into different types.

The Tuning Fork Diagram

Hubble introduced the classification scheme illustrated in the following figure, which separates most galaxies into elliptical, normal spiral, and barred spiral categories, and then sub-classifies these categories with respect to properties such as the amount of flattening for elliptical galaxies and the nature of the arms for spiral galaxies. The galaxies that do not fit into these categories are classified separately as irregular galaxies.

This diagram is termed the Hubble classification scheme, or (because of its shape) the "tuning fork diagram".

Examples of Hubble Galaxy Types

Here are some examples of specific galaxies that illustrate some of the Hubble classification types.

Observation of Galaxies

Many of the more nearby galaxies can be observed through small telescopes. Here is a table of galaxies accessible to amateur astromers.


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