These have been around for a long time, and owe their continuing popularity to their compactness. Concentric plastic disks are rotated to the date and time of day to reveal a window of the sky corresponding to what you would see. The stars are in their proper positions, and the constellations are outlined with their names. A wealth of information on the back of the wheel shows you not only how to use it, but how to predict sunrise and sunset, how to find the planets, and engage in amateur astronomy projects.
Although the planisphere will work at any North Latitude, they are optimized for the four latitudes of 22°, 30°, 40° and 50° North. They also come in two sizes of 5.5 and 10.5 inches in diameter. This is a very high quality product, and comes in a black plastic pouch which will protect it from occasional scratches. SW 1 lb.