The Milky Way

The Milky Way is our home galaxy - a vast system of hundreds of billions of stars, plus gas, dust, and dark matter.

Structure

• Disk - Flattened region about 100,000 light years across, containing most stars, gas, and dust. Spiral arms wind through the disk.
• Central bulge - Dense region of older stars around the galactic center.
• Halo - Spherical region surrounding the disk, containing globular clusters and old stars.

Our Position

The Sun is located in the Orion Spur, about 26,000 light years from the galactic center, about halfway toward the outer edge.

The Milky Way in the Sky

The Milky Way appears as a faint, cloudy band across the night sky - actually the combined light of millions of distant stars. It's best seen from dark locations during summer and winter evenings when it arches high overhead.

Spiral Arms

Major spiral arms include the Sagittarius, Perseus, and Orion arms. We see the Sagittarius Arm when looking toward the galactic center in summer, appearing as the brightest part of the Milky Way.