| R - Rate of formation of suitable stars in our galaxy (number per year) |
R = |
|
| Fp - Fraction (percentage) of those stars with planets |
Fp = |
% |
| Ne -Number of "earths" per planetary system |
Ne = |
|
| Fl - Fraction (percentage) of those planets where life develops |
Fl = |
% |
| Fi - Fraction (percentage) of sites with intelligent life |
Fi = |
% |
| Fc - Fraction (percentage) of planets where technology develops |
Fc = |
% |
| L - "Lifetime" of communicating civilizations (years) |
L = |
|
| R * Fp * Ne * Fl * Fi * Fc * L = N |
|
|
| N - Number of communicative civilizations |
N = |
|
