Frank Drake writes the equation on a board.

Drake Equation

The Drake equation, also known as the Green Bank equation and the Sagan equation, is a famous equation devised by Frank Drake that makes an attempt to estimate the number of extraterrestrial civilizations we may come into contact with in the future.[1]


This equation was devised by Frank Drake in 1960. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of such extraterrestrial civilizations. [1]

The equation is as follows:

$ N = R^{\ast} \times f_p \times n_e \times f_{\ell} \times f_i \times f_c \times L \! $


N is the number of civilizations in our galaxy with which communication might be possible;


R* is the average rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can potentially support life per star that has planets
f is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space.

Other variants of the equation exist, but the above formula is the most common.

See alsoEdit



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