What Is The Milky Way?
QUICK ANSWER
The Milky Way is our home galaxy, a barred spiral containing 100 to 400 billion stars. It's about 100,000 light years across and 1,000 light years thick. Our solar system sits about 25,000 light years from the galactic center, in a smaller spiral arm called the Orion Arm.
The Milky Way is the galaxy that contains our solar system. It's a barred spiral galaxy with several hundred billion stars, surrounded by an even larger halo of dark matter. We live in a relatively quiet part of the galaxy, about 25,000 light years from the center, far from the dense crowd of stars and supermassive black hole at the galactic core.
How big is the Milky Way?
About 100,000 light years across. According to NASA, the Milky Way's main disk has a diameter of approximately 100,000 light years and a thickness of about 1,000 light years. The galaxy contains between 100 billion and 400 billion stars, with the exact number uncertain because most stars are too dim and distant to count directly. Surrounding the visible disk is a much larger halo of dark matter extending hundreds of thousands of light years. The visible Milky Way is just the bright core of a much larger system.
What does the Milky Way look like?
A barred spiral. The galaxy has a central bulge containing many older stars, a central bar of stars, and several spiral arms wrapping outward from the bar. Our solar system is located in a smaller spiral arm called the Orion Arm, roughly 25,000 light years from the galactic center. From our position inside the galaxy, we can see the disk as a bright band stretching across the sky (the name 'Milky Way' originally referred to this hazy band). We can't easily see the overall shape of our galaxy because we're inside it.
What's at the center of the Milky Way?
A supermassive black hole called Sagittarius A*, about 4 million solar masses. The center is also packed with dense star populations, gas clouds, and ongoing star formation. The Event Horizon Telescope captured the first direct image of Sagittarius A* in May 2022. The galactic center is hidden from our view by dust clouds that block visible light, but it's visible in infrared and radio wavelengths. The center is about 26,000 light years from Earth, far enough that we're safe from its activity.
Is the Milky Way moving?
Yes, both internally and externally. The solar system orbits the galactic center at about 514,000 mph, taking roughly 230 million years per orbit. The whole Milky Way is also moving through space, on a collision course with the Andromeda Galaxy. The two will start interacting in about 4.5 billion years and eventually merge over the next several billion years. The merger won't directly affect Earth but will dramatically change the night sky.
The Milky Way is our home galaxy, a barred spiral with 100 to 400 billion stars stretching 100,000 light years across. We live about 25,000 light years from the supermassive black hole at the center. The galaxy is moving through space toward an eventual merger with the Andromeda Galaxy in about 4.5 billion years. From our position inside, we see it as a hazy band across the sky.
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