On a cold night in November, I bundled up in my coat and hat and gloves, and lugged a telescope into the backyard. I’d been given a serious mission, but first I allowed myself a few minutes of fun. I used the telescope to observe the Cigar Galaxy, the Dumbbell Nebula, Orion’s Belt. There they were, gleaming brightly in gold and blue and pink, steady friends in a painfully unsteady winter. Then I got to work. I moved the telescope across the sky until I found my target: a near-Earth asteroid. Scientists didn’t know much about it except that it would threaten life on our planet if it ever collided with us. So they’d asked amateurs like me, who happen to live somewhere with a view of the passing asteroid, to observe it and record data on it.