The Drake Equation

The Drake equation is used to estimate the number of intelligent civilizations in our galaxy. First Formulted in 1961, it estimes important parameters thought to be important for the presence of intelligent life. It states:
\[N=R^{*} \times f_p \times n_e \times f_l \times f_i \times f_c \times L\]

  - The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.
  - The rate of formation of stars suitable for the development of intelligent life.
  - The fraction of those stars with planetary systems.
  - The number of planets, per solar system, with an environment suitable for life.
  - The fraction of suitable planets on which life actually appears.
  - The fraction of life bearing planets on which intelligent life emerges.
  - The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
  - The length of time such civilizations release detectable signals into space.
None of these parameters are well know, but some calculations indicate tyhere may be 10,000 civilisations within our own galaxy. This means we will need to scan radiation from 1,000,000 star systems before we would come across one with an intelligent civilisation on a planet orbiting it.