Some of the stars may be missing. And one project is trying to find out what happened to them, while also finding more stars that have suddenly vanished or appeared. VASCO compares large surveys of the sky that were conducted decades apart. The earliest was compiled at Palomar Observatory in California in the 1950s. The survey was done with photographic plates, which have since been digitized. More-recent surveys use electronic detectors, which can see fainter objects. So anything that showed up on the Palomar plates should also show up in the later observations. VASCO has turned up quite a few objects in the early pictures that don’t show up today. Researchers have ruled out flaws in the original plates and many other possible explanations. They’re left with the idea that these objects have simply vanished. And that’s hard to explain. Stars change slowly, so most changes in brightness are gradual. Some do change over short periods, but modern surveys should easily see any variable sta
