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Drake Equation
Are there civilizations out there listening? We don't yet know the answer, but Dr. Frank Drake, president of the SETI Institute, came up with an equation that allows us to make an estimate by muliplying seven quantities related to the prevalence of life. Since its introduction in 1961, this tool has come to be known as the Drake Equation.

Use the Drake Equation to make your own estimate of the number of communicative civilizations in the Milky Way.

Light Bulb The great void in interstellar communication is not space, but time. In this animated presentation, learn how the lifetime of a civilization affects its ability to communicate.
R x Fp x Ne x Fi x Fc x L = N
R= The number of suitable stars — stars like the sun — that form in our galaxy per year.  More
Fp= The fraction of these stars that have planets. (1=100 percent. .25=25 percent.)   More
Ne= The number of Earth-like planets — meaning planets that have liquid water — within each planetary system.   More
Fl= The fraction of Earth-like planets where life develops.   More
Fi= The fraction of life sites where intelligent life develops.   More
Fi= The fraction of intelligent life sites where communication develops.   More
L= "The "lifetime" (in years) of a communicative civilization.   More
N= The number of communicative civilizations within the Milky Way today.
Your equation yields an estimated   
communicative civilizations in the Milky Way.
See Frank Drake's current estimate.
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