Drake Equation

Method of estimating the number of intelligent, technologically advanced species (i.e., able to communicate with other species) in existence in our Galaxy.

N is the number of species (life) at any given moment in our Galaxy. The parameters are as follows: R = rate of star formation in our Galaxy (in stars per year); fp = fraction of stars which have planets; ne = number of habitable planets per system with planets; fl = fraction of habitable planets upon which life arises; fi = fraction of these planets upon which life develops intelligence; ft = fraction of these planets where the intelligence develops into a technological civilization capable of communication; and L = mean lifetime of such a technological civilization. Only R and fp are known with any reliability with values of ~10 stars per year and ~1, respectively. The others are almost entirely pure speculation at this point. Calculations of N made by respectable astronomers differ by ~10 orders of magnitude. Further information on this fascinating subject may be found on the SETI website.

Some or all content above used with permission from J. H. Wittke.