This image of the brown dwarf, Gliese 229b, was created using the Hubble Space Telescope. Compared to Jupiter, Gliese is about twice as large and 40 times as massive.
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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.

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Irregular Galaxies

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