Watching the Milky Way grow up

Humans take the starry night for granted. But Earth's night sky hasn't always sparkled: In the distant past, during the infancy of the Milky Way, it was a much darker place. Now scientists have pictures of what it looked like and how it's changed. "For the first time we have images of what the Milky Way looked like in the past," said Pieter G. van Dokkum, chair of Yale University's Astronomy department and leader of a project to reconstruct the galaxy's history with data from NASA's Hubble Space Telescope. "By looking at hundreds of other distant but similar galaxies, we've traced dramatic changes in our own. We've captured most of the Milky Way's evolution." Milky Way star formation was explosive in the period between 11 billion and 7 billion years ago, the astronomers found: Nearly 90% of its stars formed then. At peak formation, about 9 billion years ago, it was generating about 15 stars a year, they said.