In his 1964 paper, "Transmission of Information by Extraterrestrial Civilizations," famed astrophysicist and radio astronomer Nikolai Kardashev addressed the types of transmissions (and at what energies) astronomers should search for in their Search for Extraterrestrial Intelligence (SETI). As part of his analysis, Kardashev proposed a universal scale for classifying the technological advancement of civilizations based on their overall energy consumption. The resulting Kardashev Scale (as it came to be known) came down to three categories.