Sci. 4-3 GalaxiesPages 110-113

A. Galaxies- large groupings of stars in space held together by the attraction of gravity

B. Edwin Hubble classified galaxies according to their shape. Major types include spiral, elliptical, and irregular galaxies.

1) Spiral galaxies- have a bulge at the center and very distinct spiral arms,

a) Most galaxies are this type of galaxy.

b) The Milky Way is a spiral galaxy.

2)Elliptical Galaxies- massive blob of stars shaped from sphere shape to cucumber shape

a) only contains old stars

3) Irregular Galaxies- galaxies that don’t fit into the other classes.

a) Many of these galaxies may have their shape distorted by neighboring galaxies’ gravity.

C.Nebula- giant clouds of gas and dust1) Some nebulas are regions where new

stars are formed from gas and dust

D. Globular Cluster- groups of older stars that look like a ball of stars

1) Globular stars clusters are found in the halos of spiral galaxies and in elliptical galaxies.

E. Open Clusters- groups of stars that are usually located along the spiral disk of a galaxy.

F.Origin of Galaxies1) Because light travels at a

certain speed, observing distant galaxies is looking back in time. Scientists look at distant galaxies to learn what early galaxies look like.

G. Quasars- a starlike source of light that is extremely far away1) Quasar may be the earliest types of galaxies ever formed2) Quasar may have enormous black holes at their center3) Quasars are among the most powerful energy sources in the

universe.