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GALAXIES |
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Galaxies are vast spinning
collections of stars, gas, and dust. Everywhere the countless billions of these celestial
cities, ranging in size from fewer than a million stars to a trillion or more, and from
tens to hundreds of thousands of light years across. Some are simple ovals packed with elderly stars, while others, like our own Milky Way, are graceful, rotating spirals with trailing arms of young stars and glowing gas. All galaxies are held together by their own gravity, but astronomers still puzzle over why galaxies are the shape they are. Galaxy classification |
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Galaxies vary widely in size, mass and brightness, but astronomers classify them into just a few main types. The 3 main groups are ellipticals, spirals, and barred spirals. These groups are then subdivided further. Other galaxies are irregular, with no obvious structure. Different types of galaxy may from, depending on the speed of the galaxy’s rotation and the rate of star formation. Spiral galaxies are all about the same size, but ellipticals can be both the largest and the smallest galaxies. |
