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Galaxies

Galaxies. What is a Galaxy?. A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants and an interstellar medium of gas and dust . Gravitationally bound- held together by gravity Stellar remnants - Leftover material from dead stars

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Galaxies

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  1. Galaxies

  2. What is a Galaxy? • A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants and an interstellar medium of gas and dust. • Gravitationally bound- held together by gravity • Stellar remnants- Leftover material from dead stars • Interstellar medium- what is in between the stars and planets

  3. How many are there? • Scientists estimate that there are more than 100 billion galaxies scattered throughout the visible universe. • Astronomers have photographed millions of them through telescopes. • The most distant galaxies ever photographed are as far as 10 billion to 13 billion light-years away. Light-Year- Distance light travels in a year in a vacuum- about 5.88 trillion miles (9.46 trillion kilometers).

  4. Sizes of Galaxies • Range in diameter from a few thousand to a half-million light-years. • Small galaxies have fewer than a billion stars. • Large galaxies have more than a trillion. • The Milky Way has a diameter of about 100,000 light-years. • Our solar system lies about 25,000 light-years from the center of the galaxy. There are about 100 billion stars in the Milky Way. • In the Northern Hemisphere we can see the Andromeda Galaxy, which is about 2 million light-years away.

  5. Shapes- Spiral • Astronomers classify most galaxies by shape as either spiral galaxies or elliptical galaxies. • A spiral galaxy is shaped like a disk with a bulge in the center. The disk resembles a pinwheel, with bright spiral arms that coil out from the central bulge. • Spiral galaxies will rotate very slowly • The Milky Way, makes a complete revolution once every 250 million years or so.

  6. Shapes- Elliptical • Elliptical galaxies range in shape from almost perfect spheres to flattened globes. • The light from an elliptical galaxy is brightest in the center and gradually becomes fainter toward its outer regions. • Elliptical galaxies rotate much more slowly than spiral galaxies or not at all.

  7. Groups of galaxies • Galaxies are distributed unevenly in space. Some have no close neighbor. Others occur in pairs, with each orbiting the other. • Most Galaxies found in groups called clusters. • A cluster may contain from a few dozen to several thousand galaxies. It may have a diameter as large as 10 million light-years. • Clusters of galaxies, in turn, are grouped in larger structures called superclusters. • One of the largest structures ever mapped is a network of galaxies known as the Great Wall. This structure is more than 500 million light-years long and 200 million light-years wide.

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