Drake equation

or Green Bank equation

Equation claimed to yield the number of technically advanced civilizations capable of interstellar communication in the Milky Way Galaxy as a function of several factors conducive to evolution of intelligent life with technological capabilities.

It was largely developed by Frank D. Drake (b. 1930) in 1961 at a SETI conference in Green Bank, W.Va. Of all the stars that form in the Galaxy, only some will give rise to life-supporting planets, and of those planets, only some will generate life capable of high technology and yet able to avoid technological destruction. Because the numbers for each factor are poorly known, the results generated vary from zero to millions.

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▪ astronomy

also called  Green Bank equation 

      equation that purports to yield the number N of technically advanced civilizations (astrobiology) in the Milky Way Galaxy as a function of other astronomical, biological, and psychological factors. Formulated in large part by the U.S. astrophysicist Frank Drake, it was first discussed in 1961 at a conference on the “search for extraterrestrial intelligence” (SETI), held at the National Radio Astronomy Observatory in Green Bank, W.Va. The equation states

N = R_*f_pn_ef_lf_if_cL.

      The factor R_* is the mean rate of star formation in the Galaxy; f_p the fraction of stars with planetary systems; n_e the number of planets in such systems that are ecologically suitable for the origin of life; f_l the fraction of such planets on which life in fact develops; f_i the fraction of such planets on which life evolves to an intelligent form; f_c the fraction of such worlds in which the intelligent life form invents high technology capable at least of interstellar radio (radio and radar astronomy) communication; and L, the average lifetime of such advanced civilizations. These numbers are poorly known, and the uncertainty increases progressively with each factor on the right-hand side of the equation. Widely quoted but at best vaguely known values for these factors are: R_* = 10/yr, f_p = 0.5, n_e = 2, f_l = 1, f_i f_c = 0.01, and thus N = L/10. Accordingly, if civilizations characteristically destroy themselves within a decade of achieving radio astronomy, which is taken as a marker of an advanced civilization, then N = l, and there are no other intelligent life forms in the Galaxy with whom terrestrial researchers can communicate. If, on the other hand, it is assumed that one percent of the civilizations learn to live with the technology of mass destruction and themselves, then N = 1,000,000, and the nearest advanced civilization would be on average a few hundred light-years away.

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