From the SETI Institute ...

                              THE DRAKE EQUATION

   How can we estimate the number of technological civilizations that
   might exist among the stars? While working as a radio astronomer at
   the National Radio Astronomy Observatory in Green Bank, West Virginia,
   Dr. Frank Drake (now President of the SETI Institute) conceived an
   approach to bound the terms involved in estimating the number of
   technological civilizations that may exist in our galaxy. The Drake
   Equation, as it has come to be known, was first presented by Drake in
   1961 and identifies specific factors thought to play a role in the
   development of such civilizations. Although there is no unique
   solution to this equation, it is a generally accepted tool used by the
   scientific community to examine these factors. The equation is usually
   written:

   N = R* x fp x ne x fl x fi x fc x L

   Where,

   N = The number of civilizations in The Milky Way Galaxy whose radio
   emissions are detectable

   R * = The rate of formation of stars suitable for the development of
   intelligent life

   f p = The fraction of those stars with planetary systems

   n e = The number of planets, per solar system, with an environment
   suitable for life

   f l = The fraction of suitable planets on which life actually appears

   f i = The fraction of life bearing planets on which intelligent life
   emerges

   f c = The fraction of civilizations that develop a technology that
   releases detectable signs of their existence into space

   L = The length of time such civilizations release detectable signals
   into space

   Within the limits of our existing technology, any practical search for
   distant intelligent life must necessarily be a search for some
   manifestation of a distant technology. A search for extraterrestrial
   radio signals has long been considered the most promising approach by
   the majority of the scientific community. Besides illuminating the
   factors involved in such a search, the Drake Equation is a simple,
   effective tool for stimulating intellectual curiosity about the
   universe around us, for helping us to understand that life as we know
   it is the end product of a natural, cosmic evolution, and for making
   us realize how much we are a part of that universe. A key goal of the
   SETI Institute is to further high quality research that will yield
   additional information related to any of the factors of this
   fascinating equation.

                               - end -

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