IntroductionThere are a number of possibilities for cosmic archaeological signals. One of the more interesting perspectives on this has been a classification scheme suggested by Nikolai Kardashev. He divided civilizations into those harvesting all the energy of a planet, of a star, and of a galaxy.
I planet (1016 W)
exosolar planetary atmospheres.
II star (4*1026 W Sun)
III galaxy (1036 W)
|Radio SETI falls below this classification so it might be type 0. A type I civilization would utilize the energy available from a planet. Signals from exosolar planetary atmospheres fall roughly in this category. A Dyson Sphere, a star cloaked in broken up planetary material, would be an example of type II. Another example would be some sort of engineering of the stellar burning process suggested by Martin Beech. A civilization using all of the energy of a galaxy would be type III. Jim Annis, an astronomer at Fermilab, has looked for type III Kardashev civilizations by plotting a surrogate for the galaxy brightness versus the size of the galaxy for 106 elliptical galaxies.|