An O’Neill cylinder would consist of two counter-rotating cylinders. The cylinders would rotate in opposite directions to cancel any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun. Each would be 6.4 kilometers (4 mi) or 8.0 kilometers (5 mi) in diameter and 32 kilometers (20 mi) long, connected at each end by a rod via a bearing system. Their rotation would provide artificial gravity.