All About Galaxies

A Galaxy, or nebula, is any large-scale system of stars, interstellar gas, dust, and plasma within the universe. The average galaxy contains more than 100 billion solar masses and ranges in diameter from 1,500 to 300,000 light-years, 90% of which is actually composed of largely unknown substance called dark matter. Individual galaxies are separated by distances in excess of millions of light years.

There are three distinct types of galaxies, including ellipticals, spirals, and irregulars. Every galaxy is controlled and held together by one central gravitational force. The Earth and its solar system are contained within the Milky Way galaxy, a large disk-shaped barred spiral galaxy about 30 kiloparsecs or 100,000 light years in diameter and 3,000 light years in width. The Milky Way galaxy is believed to contain more than three hundred billion stars, and has a total mass of six hundred billion times the gross mass of the sun.

Intergalactic space, or the space between the galaxies of the universe, is filled with an unsubstantiated plasma matter that has an average density less than one atom per cubic meter. There are believed to be more than one hundred billion galaxies within the total expanse of the universe.

For more galaxy information, including colliding galaxies, galaxy clusters, the astronomy of galaxies and more, just click on any galaxy picture, article or other interactive feature below.