Touch the Universe: A NASA Braille Book of Astronomy (2002)
Chapter: Globular Cluster NGC 6093
Figure 11.
GLOBULAR CLUSTER NGC 6093
Now let’s step back from our local area of the galaxy. Galaxies are sometimes called “star cities.” Almost every star visible to the naked eye in our night sky is located within our Milky Way Galaxy. On the clearest night, far from city lights, it is possible to see a few thousand stars, appearing as pinpoints of light against the black night sky. The Milky Way contains hundreds of billions of stars, so we actually only see a handful of the galaxy’s population.
Our Milky Way Galaxy is called a spiral galaxy because it has spiral arms in a pinwheel shape. We don’t live in the center of the galaxy; we live near a spiral arm, about two thirds of the distance from the center.
Swarming like bees around the center of our Milky Way are dense groups of stars called globular clusters. These star clusters contain hundreds of thousands of stars, all bound together by gravity. Through a small telescope, they look like “snowballs” of stars with bright centers so that the individual stars seem to “blend” together.
NGC 6093 (also called M80) is a globular cluster located 28,000 light years from Earth. What we see today is how the globular cluster looked 28,000 years ago!
The Hubble Heritage Team at NASA used the HST to capture this image of NGC 6093 in early 1999. The stars in NGC 6093 are believed to be some of the oldest stars in the universe, with ages up to 15 billion years. In Figure 11, the stars are shown as raised dots.
