Open clusters versus globular clusters
Star clusters come in two main types. Open clusters are loose groups of up to a few thousand relatively young stars that formed from the same gas cloud, and they lie mostly in the disk of the Milky Way. Globular clusters are dense, round collections of tens of thousands to millions of old stars that orbit the galaxy’s center in a halo. Because all the stars in a cluster formed together, clusters are useful for studying how stars of different masses age, which connects to our article on how long stars live.
Famous open clusters
| Name | Catalog | Constellation | Notes |
|---|---|---|---|
| Pleiades (Seven Sisters) | M45 | Taurus | Easy naked-eye cluster; stunning in binoculars |
| Hyades | Melotte 25 | Taurus | Large V-shaped group near Aldebaran, among the nearest clusters |
| Beehive (Praesepe) | M44 | Cancer | Naked-eye glow in dark skies; good in binoculars |
| Double Cluster | NGC 869 and NGC 884 | Perseus | Two clusters in one field of view |
| Wild Duck Cluster | M11 | Scutum | Rich, dense open cluster |
| Butterfly Cluster | M6 | Scorpius | Low for northern observers |
| Ptolemy’s Cluster | M7 | Scorpius | Visible to the naked eye from dark sites |
| Jewel Box | NGC 4755 | Crux | Southern sky showpiece with colorful stars |
| M35 | M35 | Gemini | Large, rich winter cluster |
| M37 | M37 | Auriga | Dense field of faint stars |
Famous globular clusters
| Name | Catalog | Constellation | Notes |
|---|---|---|---|
| Great Hercules Cluster | M13 | Hercules | The best-known globular for northern observers |
| Omega Centauri | NGC 5139 | Centaurus | The largest and brightest globular in the Milky Way |
| 47 Tucanae | NGC 104 | Tucana | Spectacular southern globular |
| M22 | M22 | Sagittarius | Bright and rich; good in summer |
| M3 | M3 | Canes Venatici | Spring favorite |
| M5 | M5 | Serpens | Bright and well defined |
| M15 | M15 | Pegasus | Compact, dense core |
| M4 | M4 | Scorpius | Close to the red star Antares |
| M92 | M92 | Hercules | Often overlooked next to M13 |
Best clusters for beginners
Start with the Pleiades, the Beehive, and the Double Cluster. All can be found with little equipment and look pleasing without a telescope, and a small 90mm telescope shows them well. For globulars, M13 is the standard first target in the northern sky, and Omega Centauri and 47 Tucanae are the southern highlights.
The largest and most beautiful
There is no official “most beautiful” cluster, so opinions vary, but the Pleiades and the Jewel Box are frequent favorites. For size, Omega Centauri is usually named the largest and most massive globular cluster in our galaxy.
Tips for observing clusters
- Use binoculars for large open clusters. A telescope’s narrow field can cut off the Pleiades.
- Globulars look like fuzzy patches in small scopes and begin to resolve into individual stars with larger apertures and higher power.
- Go to a dark site and let your eyes adapt, just as you would when watching shooting stars.
- Use a star chart or app to find each cluster’s constellation first; our famous constellations guide helps with the big patterns.
- Remember that every point of light in a cluster is a distant sun, not a planet; see how a star differs from a planet if you need help telling points of light apart.
FAQ
What are the most famous star clusters? The Pleiades, the Beehive, the Double Cluster, M13, and Omega Centauri are among the best known.
What is the largest known star cluster? Omega Centauri is usually cited as the largest globular cluster in the Milky Way. Other kinds of clusters, including young massive ones in other galaxies, can be larger.
What are the main types of star clusters? Open clusters and globular clusters.