### Drake equation

(estimate of advanced life in the Milky Way)

The **Drake equation** is a well-known example of a
model to estimate the number of detectable extraterrestrial
advanced civilizations in the galaxy,
a number of interest in
the field of **SETI** (**search for extraterrestrial intelligence**).
It was formulated by astronomer Frank Drake in 1961.
The equation:

*N = R*_{*} × f_{p} × n_{e} × f_{l} × f_{i} × f_{c} × L

where:

- N - the number.
- R
_{*} - average rate of star formation in the galaxy.
- f
_{p} - average fraction of those stars with planets.
- n
_{e} - average number of life-supportable planets in such systems, i.e., in the habitable zone and so forth.
- f
_{l} - fraction of those that actively develop life.
- f
_{i} - fraction of those that develop intelligent life.
- f
_{c} - fraction of those that develop technology that can release detectable signals.
- L - length of time for which such systems release detectable signals.

(*equation,exoplanets,life,astrobiology*)
http://en.wikipedia.org/wiki/Drake_equation

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