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Local Group

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© Chris Butler, Don Dixon, Bruce Bohannon, Griffith Observatory

Our galactic neighborhood contains the Milky Way Galaxy, the nearby Andromeda Galaxy, and nearly a dozen smaller companions. Members of the Local Group move together through space. Each one has millions or billions of stars, and our Sun is only one starry member of the Milky Way.

Our galaxy and Andromeda will collide in a few billion years. Because galaxies are mostly empty space, this event will probably be more of a mixing of stars and gas than a crash.

The Scale of the Local Group

© Laurie HatchThe distance from Earth to the nearest star is about 25 trillion miles (40 trillion km). The nearest galaxy lies much farther across empty space. At this scale, miles or kilometers are impractical ways to measure distance, so we use the light-year. This is the distance that light travels in a year: 5.8 trillion miles (9.3 trillion km).

Science fiction stories often feature faster-than-light ships. We don’t have such ships yet. Today the only way to explore across such large distances is through telescopes. And, when we look at the Andromeda Galaxy, more than two million light-years away, we see it as it looked more than two million years ago. In a sense, our observatories also act as time machines, giving us a view back through cosmic history.

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