N = R* * fp * ne * fl * fi * fc * L
The Drake Equation, formulated by astronomer Frank Drake in 1961, is used to calculate the number of civilizations in the Milky Way capable of interstellar communication. The variables of this equation are as follows:
N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.
R* =The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc= 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.