The Carnegie 20-inch (510 mm) twin refractor is located in a mid-sized dome at the observatory. Because the Carnegie is actually two 20-inch (510 mm) telescopes, side by side on a single mount, it looks more like a large set of very long binoculars rather than a telescope. One side is designed to photograph blue light and the other yellow light.
The Carnegie was built expressly to measure the motions of as many stars as possible in our local area of the Milky Way. Called the Lick Proper Motion Survey, the Carnegie's mission was to photograph the entire night sky twice; once in the 1950s and again 20 years later. By comparing both sets of photographs, much was learned about the motion of stars and the structure of our galaxy. The Carnegie is not used today except when photographs of a wide area of the sky are needed.
Location of Carnegie telescope