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
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