Globular Star Clusters
Although open clusters appear as a scattering of stars that is more dense than the background star field,
globular clusters look like a compact ball of stars. In some cases the globular is made up more than a
million stars and may be more than a hundred light years in diameter. The globulars found in the Milky
Way appear to orbit our galaxy center in a spherical halo, much the same way that satellites orbit the Earth.
Globulars are thought to be some of the oldest structures in our galaxy and may have formed soon after
the big bang. Currently there are about 160 known globulars in the Milky Way. Other galaxies also contain
globular clusters and as with the Milky Way, they are found in a halo surrounding the galaxy. For example,
the Andromeda galaxy is thought to have about 500 globular clusters. G1, Andromeda's largest globular
cluster, can be seen here. The huge eliptical galaxy M87 is thought to have thousands.
The unusual spherical distribution of globular clusters around the outer reaches of the Milky Way has some
historic importance. The astronomer Harlow Shapley studied this distribution and concluded from it that the
center of our galaxy was at a considerable distance from Earth (1917). Prior to his proposal most thought
that our solar system was near the center of the Milky Way rather than on its periphery. While Shapley's
conclusion remained controversial for a few years, it was eventually accepted by most astronomers. His
technique is still considered one of the primary means of determining the distance to the center of our
Galaxy.
globular clusters look like a compact ball of stars. In some cases the globular is made up more than a
million stars and may be more than a hundred light years in diameter. The globulars found in the Milky
Way appear to orbit our galaxy center in a spherical halo, much the same way that satellites orbit the Earth.
Globulars are thought to be some of the oldest structures in our galaxy and may have formed soon after
the big bang. Currently there are about 160 known globulars in the Milky Way. Other galaxies also contain
globular clusters and as with the Milky Way, they are found in a halo surrounding the galaxy. For example,
the Andromeda galaxy is thought to have about 500 globular clusters. G1, Andromeda's largest globular
cluster, can be seen here. The huge eliptical galaxy M87 is thought to have thousands.
The unusual spherical distribution of globular clusters around the outer reaches of the Milky Way has some
historic importance. The astronomer Harlow Shapley studied this distribution and concluded from it that the
center of our galaxy was at a considerable distance from Earth (1917). Prior to his proposal most thought
that our solar system was near the center of the Milky Way rather than on its periphery. While Shapley's
conclusion remained controversial for a few years, it was eventually accepted by most astronomers. His
technique is still considered one of the primary means of determining the distance to the center of our
Galaxy.
| Omega Centauri |
| M3, 5 x 5 min Lum, C9.25 f/5, ST10XME with AO8 |
| M53, 5 x 5 min Lum, C9.25 f/5, ST10XME with AO8 |
| M5, 5 x 5 min Lum, C9.25 f/5, ST10XME with AO8 |
| M13 in color, 10 x 5 min Lum, 3 x 5 min each RGB, C9.25 f/5, ST10XME with AO8 |
| M13 b/w 10 x 5 min Lum, C9.25 f/5, ST10XME with AO8 |