Galaxies - Star Cities



A diagram which shows the many types of galaxies and their special names
Click on image for full size (29K JPEG)
When we look up at the night sky, we notice that there are many stars in our sky. Stars must like to live together in star cities - galaxies. Our city of stars is called the Milky Way, and it is home to 100 billion stars, including the Sun. The stars stay together because of the force of gravity. There are as many other galaxies in our universe as there are stars in our Galaxy!

Galaxies come in different shapes and sizes. They can be circular or shaped like an egg (elliptical), or appear as pretty pinwheels (spirals). Some galaxies don't seem to fit into these groups, so they are called irregulars.

A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF

Galaxies



The Hubble "tuning fork" diagram shows the many types of galaxies and their classifications
Click on image for full size (29K JPEG)
During the early 1900's, which is not very long ago, astronomers were unaware that there were other galaxies outside our own Milky Way Galaxy. When they saw a small fuzzy patch in the sky through their telescopes, they called it a nebula. When examined closely, some of the nebulae had a spiral shape. So astronomers at first called these "spiral nebulae". These nebulae were all believed to be part of our Galaxy, our community of stars.

Edwin Hubble studied the "spiral nebulae" and found that they were composed of stars. These nebulae were not nebulae at all, but other communities of billions of stars held together by gravity - galaxies! Suddenly, our universe was much bigger. We realized that our Galaxy was just one of many billions of galaxies in the universe.

Hubble studied galaxies for a very long time, and after seeing many, many galaxies, he realized that he could put them into groups based on their shape: spirals, ellipticals, or irregulars. His work helped us to understand that the appearance of galaxies depends on our point of view, and on what's happening in the galaxies.

A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF

Galaxies



The Hubble "tuning fork" diagram shows the many types of galaxies and their classifications
Click on image for full size (29K JPEG)
The introduction of telescopes to the study of astronomy opened up the universe, but it took some time for astronomers to realize how vast the universe could be. Telescopes revealed that our night sky was not only populated with stars, but with other, more nebulous objects. Some of these objects were nebulae within our Galaxy, the Milky Way. As telescopes became more powerful, it was possible to see that some of the nebulae had a spiral-like structure. These were also believed to be part of our Galaxy and thus relatively nearby.

In 1920, two important astronomers, Harlow Shapley and Heber D. Curtis, held a great debate about the nature of these "spiral nebulae". Were they objects within the Milky Way, or were they communities of stars distinct from our Galaxy? Edwin Hubble studied these "spiral nebulae" and found that they were composed of stars, and thus resolved the debate. These nebulae were not nebulae at all, but galaxies! Suddenly, our universe was much bigger. We realized that our Galaxy was just one of many billions of galaxies in the universe.

Hubble continued to study galaxies his entire career, and we owe much of our understanding of galaxies to him. His observations led to the current classification of galaxies as spirals, ellipticals, or irregulars, and to our knowledge that the appearance of these galaxies depends both on our perspective, and on the forces which form and power galaxies.

A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF


Last modified prior to September, 2000 by the Windows Team

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