EVERYTHING YOU NEED TO KNOW ABOUT THE MILKY WAY

The Milky Way is our home galaxy – a vast star factory with a monstrous black hole at its heart. Join our tour of the cosmic pinwheel that’s home to every star we can see in the night sky

- Giles Sparrow

SPIRAL IN SPACE

The shape of the Milky Way in the sky reveals that our Solar System is embedded in a broad but thin plane of stars. Looking away from the band of the Milky Way, we see past the relatively nearby stars that lie in our part of this plane into apparently empty intergalactic space. However, when we look across the plane we see many more stars extending to greater distances; their combined light forms the band of the Milky Way. Radio astronomy observations, which can see past dense clouds of stars and dust to map the distribution of hydrogen gas clouds across the plane, confirm that our galaxy has a spiral structure broadly similar to many other galaxies in the sky – in fact, it’s a type of galaxy known as a barred spiral.

The latest measurements suggest the Milky Way is a flattened disc roughly 100,000 light years in diameter and about 1,000 light years deep – although stray trails of stars extend much further out. Stars, gas and dust in the disc slowly orbit around a central bulge of stars roughly 20,000 light years across in the direction of Sagittarius. The spiral arms are concentrations of particularly bright stars and star-forming nebulae that run across the disc, beginning at either end of an elongated stellar bar that extends from the bulge. In total, the Milky Way is thought to contain between 100 billion and 400 billion stars, with our own Solar System located about 26,000 light years from the centre, roughly midway between the two major spiral arms in a region called the Local Arm or Orion Spur.

1 Norma Arm