
From 150,000
observed stars, 42,000 similar
to our sun and belong to spectral class G.
This corresponds to a share of 28 %
of all observed stars. The probability factor
extrapolated for the occurrence of G stars in our
galaxy is therefore: 
F_{s} = 0.28 =
42,000:150,000 = 7:25
Related
to all star systems A in our galaxy, the
number N_{s} of
the solarlike star systems results with:
1.4.1 Equation 
N_{s}
= A · F_{s} 

with the following factors:
A = (100 – 300)·10^{9} 
Number of Suns in the Galaxy 
F_{s}
= 0.28 = 7:25 
Probability factor for solarlike
stars 


Insert the
factors into equation 1.4.1: 


1.4.2 Theorem 
The number of star systems,
with sunlike stars, in our galaxy is 28 to 84
billion. 
