As the Chilean ash cloud wafts through Australian airspace for a second time, we’re all thrown back into the science of prediction. What will it do next? Nightly news footage of passengers sitting in grumpy heaps in airports has drawn an unusual degree of national attention to Darwin. It turns out that we have one of the world’s nine Volcanic Ash Advisory Centers right here in Australia, and they’ve been putting on their good shirts for the TV cameras night…