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What is the Milky Way Galaxy?

The Milky Way Galaxy as seen in the night skyThe Milky Way Galaxy as seen in the night skyThe Milky Way Galaxy is the galaxy to which our own star, the Sun, belongs. Sometimes called, simply, the Galaxy, it is a vast, flat, spiral of stars. It is named after the misty band of stars in the night sky—actually our side-on view of one of its spiral arms. The Galaxy contains about 200 billion stars and measures about 100,000 light years across. It spins at 250 kilometres per second (150 miles/sec) and takes more than 200 million years to complete one full circle.

Nucleus and arms

The Milky Way GalaxyThe Milky Way GalaxyThe Galaxy has a bulge at its centre, called the nucleus. Here older, red stars are concentrated. Four giant arms spiral out from the nucleus. Younger blue stars are found in the outer reaches of these arms, amid clouds of gas and dust where new stars are forming. The Sun is situated on one of the spiral arms, roughly halfway out from the nucleus. Here are mostly yellow and orange young-to-middle aged stars.

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The word galaxy comes from the Greek word "galaxias", meaning "milky one".

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