The Milky Way Galaxy
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A galaxy is a collection or grouping of stars, nebulae, gases, etc. that are part of the universe. Milky Way is the galaxy of which the sun and solar system are a part. It looks like a band of light across the night sky. The Milky Way rotates or moves around the center of the galaxy. The Milky Way galaxy is moving at a speed of around 370 miles per second or around 590 kilometers per second. The sun is moving at a speed of around 150 miles per second or around 240 kilometers per second in a circular orbit around the Milky Way galaxy. It takes 200 - 230 million years to complete one revolution.
The Milky Way is a large spiral galaxy of about a hundred billion stars. It appears as a flattened sphere with a bulge in the center of stars. From the center spiral arms extend. Our sun is on an outer arm. The diameter of the Milky Way is around 100,000 light-years, its thickness is 10,000 light-years and is 30,000 light-years at the center.
The stars, gas, and dust that make up the Milky Way can be placed into two broad star populations. The spiral arms and central plane of the Milky Way hold the interstellar gas, dust, and bright young stars called Population I. The halo, spaces between the spiral arms, and central core of the galaxy contain the older, less luminous stars that are called Population II.
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