From a human perspective, Earth-crossing asteroids can have good timing or bad timing. Good timing is when the asteroid and the Earth don't meet. Bad timing is when they do. Astronomers say that a 1,000-foot diameter asteroid discovered last year may have bad timing. There is a slight possibility that the rock, 99942 Apophis, will hit Earth in 2036 after coming within about 20,000 miles in 2029. A collision could cause regional devastation on a scale far worse than last year's tsunami. "The most likely thing is that it is not going to be a threat," said Rusty Schweikart, the...