A star cluster with a lot of deceptively young-looking stars ascends the eastern sky tonight. It’s to the upper left of the bright yellow-orange star Arcturus, which climbs into good view by about 10 o’clock. The cluster is visible through binoculars as a small, round, faint smudge of light. M3 is a tight ball of half-a-million stars known as a globular cluster. It spans a couple of hundred light-years, although most of its stars are jammed together in the middle. They’re so tightly packed that each star probably has thousands of neighbors within just five light-years; by comparison, only one star system is that close to the Sun. Among M3’s myriad stars are many that appear to be much younger than they really are. M3 probably was born more than 11 billion years ago. All of its most vigorous stars, which were bright and blue, have long since died. So the cluster’s remaining stars should be fairly red. Yet M3 contains quite a few blue stars, known as blue stragglers. The leading ideas su
