Complex sentence: Finally, almost four years after his previous discovery, an unknown comet found its way into his eyepiece on 03 July 1996 while he swept the rear legs of Leo the Lion with his 8-inch scope.
Split into simpler sentences: Finally, almost four years after his previous discovery, an unknown comet found its way into his eyepiece on 03 July 1996. He was sweeping in the rear legs of Leo the Lion with his 8-inch scope.