In Astrophysics
- Star cluster, referring to both open and globular clusters
- Open cluster, a spherical collection of stars that orbits a galaxy in the galactic plane
- Globular cluster, a spherical collection of stars whose orbit is either partially or completely in the halo of the parent galaxy. They are older, more densely populated, and contain more stars than open clusters.
- Galaxy groups and clusters, large gravitationally-bound groups of galaxies, or groups of groups of galaxies
- Supercluster, the largest gravitationally bound objects in the universe, composed of many galaxy clusters
- Cluster mission, a European Space Agency mission to study the magnetosphere
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