8 
The Astronomical Survey of the Universe [oh. i 
parallaxes for the three stars, 61 Cygni, a Lyrae and a Centauri. It had at 
last been found possible to sound the depths of space and the universe lay 
open for exploration. As the result of the labours of many astronomers, the 
parallaxes of over 2000 stars are now known with high accuracy. In the 
great majority of cases the errors of the determinations lie well within a 
hundredth of a second of arc, which is the angle that a pin-head subtends at 
a distance of ten miles. 
In Table I (p. 7) will be found a list of all the stars which are at present 
known to lie within a distance of 5 parsecs of the sun. 
Density of Distribution of Stars. 
7 . There is no reason for expecting any special concentration of stars in 
the immediate neighbourhood of the sun. If our nearest neighbours in space 
are distributed approximately at random, the number of stars within a sphere 
of any radius drawn round the sun should be approximately proportional to the 
volume of the sphere, and therefore to the cube of its radius. 
Fig. 1. Density of Distribution of known Stars in the neighbourhood of the Sun. 
Fig. 1 shews the distribution of known stars in the neighbourhood of the 
sun. The abscissa measures distances from the sun in parsecs, while the 
ordinate gives the number of known stars per cubic parsec within this 
distance. The uppermost (thick) curve refers to the total of known stars of 
all kinds, the chain curve refers to stars which emit at least a thousandth