What is the Milky Way
The Milky Way is a massive spiral galaxy, which means it has a flat, rotating disk with curved spiral arms extending outward. It contains hundreds of billions of stars, along with gas, dust, and dark matter. At the center of the Milky Way is a supermassive black hole called Sagittarius A* that is millions of times more massive than our Sun. The entire galaxy rotates slowly, taking about 230 to 250 million years for our solar system to complete one full orbit around the center.
Where Earth is Located
Earth is part of our solar system, which orbits within one of the Milky Way's spiral arms called the Orion Arm or Orion Spur. Our solar system is positioned about 26,000 light-years away from the galaxy's center. We are located in what scientists call the Local Bubble, a region of hot, ionized gas surrounded by cooler clouds of gas and dust. Our position is relatively far from the galaxy's crowded center, making our solar system a quieter corner of the Milky Way.
Structure and Size
The Milky Way is approximately 100,000 light-years in diameter, though recent observations suggest it may be larger. The galaxy has a central bulge where billions of stars crowd together tightly, and from this bulge, several spiral arms curve outward in a rotating disk. The disk is surrounded by a spherical halo of older stars and globular clusters. The entire structure is held together by gravity and contains an enormous amount of dark matter that we cannot see directly but know exists because of its gravitational effects.
How We Know About the Milky Way
Because we live inside the Milky Way, we cannot see its complete shape from Earth. Scientists determine the galaxy's structure by observing radio waves and infrared light from distant gas and dust clouds, as well as by studying the motions of stars around the galactic center. Space telescopes and ground-based observatories have allowed astronomers to map out the locations of billions of stars and create detailed pictures of the galaxy's spiral structure. 
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