What is the Milky Way What is the Milky Way Like?Like?

Chapter 31.1Chapter 31.1

Since we are inside it, we cannot see Since we are inside it, we cannot see the whole galaxythe whole galaxy From Earth, there is a band of stars From Earth, there is a band of stars

across the sky. This is what we see across the sky. This is what we see because we’re looking through the because we’re looking through the galaxy edge on.galaxy edge on.

By mapping the location of stars, By mapping the location of stars, astronomers were able to determine astronomers were able to determine the center of the Milky Waythe center of the Milky Way

This allowed them to determine that This allowed them to determine that the Milky Way had a disc shape with the Milky Way had a disc shape with a central “bulge” of stars.a central “bulge” of stars.

To determine if the Milky Way had To determine if the Milky Way had spiral arms, astronomers had to map spiral arms, astronomers had to map the density of hydrogen.the density of hydrogen.

From this they determined that the From this they determined that the Milky Way is a spiral galaxy, with Milky Way is a spiral galaxy, with about 100,000,000,000 (100 billion) about 100,000,000,000 (100 billion) stars, about 100,000 light-years stars, about 100,000 light-years acrossacross

In the center is a massive black holeIn the center is a massive black hole

Looking at the age of the stars, it Looking at the age of the stars, it was noted that the oldest stars are in was noted that the oldest stars are in the center of the galaxy and the the center of the galaxy and the globular clusters, and the youngest globular clusters, and the youngest in the armsin the arms

This tells us that the galaxy first This tells us that the galaxy first formed from a spherical cloud. The formed from a spherical cloud. The stars of the globular clusters formed, stars of the globular clusters formed, the cloud collapsed taking on a disc the cloud collapsed taking on a disc shape. The stars in the center shape. The stars in the center formed, and finally the stars in the formed, and finally the stars in the arms. arms.