Field guide · Deep sky
Globular clusterGlobular cluster
A tight ball of hundreds of thousands of ancient stars orbiting the galaxy like a moth round a lamp. Many are older than almost anything else in it.
- Stars
- 100,000 to a few million
- Age
- Usually 10–13 billion years
- Where
- In a halo around the galaxy
- Best seen with
- A telescope, the bigger the better
Where an open cluster is a loose family of young stars, a globular is a dense city of old ones: hundreds of thousands of stars packed so tightly towards the centre that a telescope cannot split them.
They are fossils. Most formed over twelve billion years ago, when the galaxy itself was assembling, and they orbit in a great halo around it rather than in its disc. The Milky Way has about 150. In 1918 Harlow Shapley used their positions to show that the Sun is nowhere near the centre of the galaxy: they are bunched towards Sagittarius because that is where the centre is.
In binoculars a globular is a fuzzy star. In a telescope it becomes a drift of sugar that seems to keep resolving the longer you look.
See it in the sky
Each one opens the sky map pointed at it, for tonight, from where you are.
- Globular cluster Great Star Cluster in Hercules The Great Cluster in Hercules, the northern showpiece.
- Globular cluster ω Cen Cluster Omega Centauri, the biggest — possibly the core of an eaten galaxy.
- Globular cluster 47 Tuc 47 Tucanae, beside the Small Magellanic Cloud.
- Globular cluster Great Sagittarius Cluster In Sagittarius, one of the nearest.