The Smithsonian Institution was founded in 1846 by an Act of Congress as "an establishment for the increase and diffusion of knowledge." Smithsonian Institution consists of 21 Museums (including the top three most visited museums in the world) and the National Zoo. There are over 150 affiliated museums in 39 states, Panama and Puerto Rico, and traveling exhibitions throughout America that visit over 100 museums every year. Smithsonian Institution has 700 world-class scientists on staff and nine research centers around the globe; and over 136 million artifacts - from Dorothy's ruby slippers to the Lunar Orbiter.