Milky Way

Viewed from above, a bar-shaped swarm of stars cuts across the bright central bulge, and from each end of the bar several spiral arms coil outward like a whirlpool — the classic look of a "barred spiral." Because we sit inside one of those arms (the Orion Arm) and see the galactic disk edge-on, in our sky it appears as a hazy band of light — the Milky Way.

The Milky Way is a barred spiral galaxy roughly 100,000 light-years across, home to the Sun and more than a hundred billion other stars, along with nebulae, star clusters, and the enigmatic dark matter. The Sun lies in an outlying spiral arm about 26,000 light-years from the galactic center and orbits that center at about 220 km/s, taking over 200 million years to complete a single lap. At the very heart of the galaxy sits "Sagittarius A*," a supermassive black hole about 4 million times the mass of the Sun. The band of light crossing our night sky is simply this disk seen edge-on from within.