Vigilant amateur asteroid hunters keep watch for menacing space rocks

In the Mojave Desert of Southern California, Bob Stephens has a wide view of the cosmos, where space rocks whiz in all directions. But Stephens is intent on making sense of that chaos. Some of his latest projects: tracking an asteroid he suspects to have a moonlet; co-authoring a couple of scientific papers on asteroids in Jupiter's midst; and observing an unusual asteroid that appears to be tumbling rather than spinning like a top. It sounds like a full-time job, but this is just his pastime. S...