Galaxies

Megaparsecs: used by astronomers to measure great distance (equals 3, 260, 000 light-years)

Most distant galaxies that are still visible using large telescopes and photography are 3,000 megaparsecs away from earth.

Definition: groups of (a differing number of) galaxies, ranging from a few to the thousands.

Rich clusters: clusters with over a thousand galaxies that are more concentrated toward their centers, and often have a giant elliptical galaxy at their centers. Example: virgo cluster.

Poor clusters: clusters with fewer than a thousang galaxies, many with irregular shapes/forming small groups called subclusters. Example: The Local Group.

A group of approx. 20 galaxies all in the same area.

Two main members: Milky Way and Andromeda (next most important: Triangulum).

Emit large amounts of radio waves

Some emit over ten million times as much radio-wave energy as normal galaxies.

Extremely bright, distant galaxies that look like stars and change in brightness

Far away: from one bliion to fifteen billion light-years from earth

Can be 1,000 times brighter than a normal galaxy