Definition

THE PRINCIPLE OF SEARCH

DRAKE EQUATION
N = R * x f p x n e x f l x f i x f c x L
The terms in the equation can be explained as follows
o N - Number of communicative civilizations
o R* - Average rate of formation of stars over the lifetime of the galaxy (10 to 40 per year)
o fp - Fraction of those stars with planets (0 < fp <1, estimated at 0.5 or 50 percent)
o ne - Average number of earth-type planets per planetary system (0 < ne <1, estimated at 0.5 or 50 percent)
o fl - Fraction of those planets where life develops (0 < fl <1, estimated at 1 or 100 percent)
o fi - Fraction of life that develops intelligence (0 < fi <1, estimated at 0.1 or 10 percent)
o fc - Fraction of planets where intelligent life develops technology such as radio (0 < fc <1, estimated at 0.1or 10 percent)
o L - Lifetime of the communicative civilization in years (estimates are highly variable, from 100s to 1000s of years, approximately 500 years for example purposes)

BASIC PROBLEMS IN SEARCH

" How to search such a large area of sky
" Where to look on the radio dial for ET
" How to make the best use of the limited radio-telescope resources available for SETI

Large vs. Small Areas of Sky
Wide-field search - In this method large chunks of the sky are searched at a low resolution within a short period of time.
Targeted search - In this method, intensive investigations of a limited number of sun-like stars are made for ET signals.
What's the Frequency?
In the 1- to 10-gigahertz (GHz) range of frequencies, there are two frequencies: 1.42 GHz, caused by hydrogen atoms, and 1.65 GHz, caused by hydroxyl ions. This area is called as the water hole.

Limited Radio-telescope Resources
" Conduct limited observing runs on existing radio telescopes
" Conduct SETI analyses of radio data acquired by other radio astronomers (piggyback or parasite searches)
" Build new radio telescopes that are entirely dedicated to SETI research