Celestron 1.25" 90° Prism Star Diagonal lets you view objects that are at a 90° angle from the direction the telescope is pointing, thereby allowing comfortable viewing when the telescope is pointed at, or near, the zenith (i.e. directly overhead). The resulting image is right side up, but will be reversed from left to right. This Celestron 1.25" 90° Prism Star Diagonal is an inexpensive accessory which will "pay for itself" in convenience, the first couple of nights you observe with your telescope.