Had you been alive at the dawn of the solar system, the night sky would have been bright enough to read by. A thousand or so stars formed within a few light-years from the same interstellar cloud the sun did.
Ron Miller

Key Concepts

• The sun is a solitary star, and astronomers have traditionally assumed it formed as such. Yet most stars are born in clusters, and scraps of evidence from meteorites and from the arrangement of comets suggest that our sun was no exception.
• Its birth cluster could have contained 1,500 to 3,500 stars within a diameter of 10 light-years—a big, unhappy family whose larger members bullied the small fry and which broke up not long after our solar system came into being.
• Although the sun’s siblings have long since dispersed across the galaxy, observatories such as the European GAIA satellite will be able to look for them. Their properties might fill in the gaps of the solar system’s deep history.

People have often sought solitude in the starry night sky, and it is an appropriate place for that. The night is dark because, in cosmic terms, our sun and its family of planets are very lonely. Neighboring stars are so far away that they look like mere specks of light, and more distant stars blur together into a feeble glow. Our fastest space probes will take tens of thousands of years to cross the distance to the nearest star. Space isolates us like an ocean around a tiny island.

Yet not all stars are so secluded. About one in 10 belongs to a cluster, a swarm of hundreds to tens of thousands of stars with a diameter of a few light-years. In fact, most stars are born in such groups, which generally disperse over billions of years, their stars blending in with the rest of the galaxy. What about our sun? Might it, too, have come into existence in a star cluster? If so, our location in the galaxy was not always so desolate. It only became so as the cluster dispersed in due time.

   
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