On a field just below the summit of Crawford Hill, the highest point in Monmouth County, N.J., almost within sight of the skyscrapers of Manhattan, sits a cluster of shacks and sheds. Next to them is the Holmdel Horn Antenna, a radio telescope somewhat resembling the scoop of a giant steam shovel: an aluminum box 20 feet square at the mouth and tapering to an eight-inch opening, through which the radio waves are funneled into the “cab,” a wooden hut on stilts. From a distance, the whole site could be mistaken for an old mining camp you might come across in Montana or Idaho.