The Pleiades

At 444 light-years, the Pleiades is one of the closest star clusters to Earth — close enough that you can see six or seven of its stars without a telescope on any clear winter night. The blue glow surrounding them isn’t leftover material from their birth. It’s a coincidence: the cluster is drifting through an unrelated cloud of interstellar dust, and the hot blue stars are lighting it up like headlights in fog. The cluster is young by stellar standards — about 100 million years old — and its stars will eventually drift apart over the next few hundred million years.