During the solar eclipse on Monday, when approximately 89 percent of the sun was blocked out by the moon here, it was both a communal and a solitary experience for those taking it in at a watch party at the South Fork Natural History Museum in Bridgehampton. The field behind the museum was dotted with 100-plus voyeurs, in small groupings on lawn chairs and blankets, staring with solar-safe spectacles, taking in every second of the hot action.