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Beyond the Solar System
Galaxies: Cities of Stars
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Stars beyond counting populate the universe. Most reside in dense groups known as galaxies. These 'island universes' come in many shapes and sizes, and contain anywhere from a few million stars to a trillion or more. Some are still churning out lots of new stars, while others are quietly living out their lives. And some galaxies are merging to form even bigger cities of stars. More »

Types of Galaxies
NGC 1365 is an example of a 'barred' spiral, with a thick bar of stars extending from the core.
Galaxies can be classified in several ways. The most common is a system developed by Edwin Hubble, which is based on the shapes of galaxies. More » 		Galaxy Formation
Two galaxies -- NGC 2207 (left) and IC 2163 -- that are beginning to merge.
One of the greatest challenges facing astronomers today is understanding how galaxies form. More »
Great Dates

1755
Immanuel Kant proposes that spiral 'nebulae' are really vast agglomerations of stars outside the Milky Way

1845
William Parsons, Lord Rosse, is the first to note that some 'nebulae' show a spiral structure

1864
William Huggins notes that the spectra of many 'nebulae' are different from those of stars

1923
Edwin Hubble discovers that M31 (and therefore, all galaxies) lies far outside the Milky Way

1951
Astronomers first measure the spiral structure of the Milky Way

1963
Maartin Schmidt finds that quasars are very far away, which means they are extremely powerful

Galaxies Fade

Eventually, the stars of the Milky Way will burn out as will the stars in other galaxies sprinkled through the universe. More » 		The Milky Way
The vast Milky Way contains a myriad of features, including star clusters, stellar nurseries, and a jumbled region of stars, gas, and magnetic fields in the core.
The Milky Way consists of a bulge of stars in the core, probably a thick bar of stars flanking the core, and bright spiral arms wrapping around the core. More »
The Local Group
A section of the starry disk of M31, the Andromeda galaxy.
The Milky Way galaxy is part of a larger cosmic neighborhood -- a collection of more than 35 galaxies known as the Local Group. More » 		See Also...

How Far? Astronomers use several techniques to measure the distances to galaxies.

Quasars and supermassive black holes. Texas astronomers are shedding light on these mysterious objects in distant galaxies.

Keywords about galaxies and cosmology

FAQs about galaxies and cosmology

This document was last modified: October 19 2009.

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