Pleiades

The Pleiades is the most famous open star cluster in the sky, visible to the naked eye across all inhabited parts of Earth and referenced in the mythologies of cultures from Greece to Japan, the Americas, and Australia. It contains roughly 1,000 confirmed members, of which the “Seven Sisters” — the seven brightest stars — are the most prominent.

The cluster is approximately 100 million years old — young by stellar standards — and dominated by hot, luminous blue-white B-type stars. The surrounding blue nebulosity visible in long-exposure photographs is not related to the cluster’s formation but is instead interstellar dust the cluster is currently passing through. The dust reflects the blue light of the hot stars, creating the characteristic pale-blue reflection nebula.

Hubble imaging of the Pleiades core resolves individual stars and their surroundings in detail impossible from the ground, revealing brown dwarf candidates and low-mass cluster members through their infrared signatures.

The cluster will continue to disperse over the next several hundred million years as individual members gradually drift apart due to gravitational interactions and the tidal forces of the Milky Way.