Complex sentence: The resulting images taken during its rapid flyby reveal that Rama is a perfect cylinder, in diameter and long, made of a completely featureless material, making this humankind's first encounter with an alien space ship.
Split into simpler sentences: The resulting images taken during its rapid flyby reveal that Rama is a perfect cylinder, in diameter and long, made of a completely featureless material. In other words, this is humankind's first encounter with an alien space ship.