The Nearer Stars 
5 
-4] 
such as the moon, other planetary satellites and comets, we must give first 
place to the planets Venus and Mars, which approach to within 26 and 35 
millions of miles of the earth respectively. Next in order comes Mercury with 
a closest approach of 47 million miles, and then the sun at about 93 million 
miles. Other planets follow in turn until we reach Neptune at a distance of 
2800 million miles. 
After this comes a great gap—the gap which divides the solar system from 
the rest of the universe. The first object on the far side of the gap is the faint 
star Proxima Centauri, at a distance of no less than 25,000,000 million miles, 
or more than 8000 times the distance of Neptune. Close upon this come the 
two components of the binary star a Centauri at 25,300,000 million miles; 
these, with Proxima Centauri, form a triple system of stars which are not only 
near together in the sky, but are voyaging through space permanently in one 
another’s company. After these come three faint stars, Munich 15,040, Wolf 
359, and Lalande 21,185, at 36, 47 and 49 million million miles respectively, 
and then Sirius, the brightest star in the sky, at 51 million million miles. 
Comparing these distances with the distances of the planets, we see that the 
nearest stars are almost exactly a million times as remote as the nearest 
planets. 
A simple scale model may help us to visualise the vastness of the gulf 
which divides the planets from the stars. If we represent the earth’s orbit by 
a circle of the size of the full stops of the type used in this book (circles of a 
hundredth of an inch radius) the sun becomes an entirely invisible speck of dust 
and the earth an ultra-microscopic particle a millionth of an inch in diameter. 
On this same scale the distance to the nearest star, Proxima Centauri, is about 
75 yards, while that to Sirius is about 150 yards. We see vividly the isolation 
of the solar system in space and the immensity of the gap which separates the 
planets from the stars. 
Before parting from this model, let us notice that the distance of one 
hundred million light-years to the farthest object so far discussed by 
astronomy is represented on the same scale by a distance of about a million 
miles. In this model, then, the universe is millions of miles in diameter, our 
sun shrinks to a speck of dust and the earth becomes less than a millionth part 
of a speck of dust. The inhabitant of the earth may well pause to consider 
the probable objective importance of this speck of dust to the scheme of the 
universe as a whole. 
4 . The ancients were, for the most part, entirely unconscious of the 
enormous disparity in size between the earth and the rest of the universe. 
But those few who urged that the earth moved round the sun, saw that this 
motion must necessarily cause the nearer stars to change their positions 
against the background provided by the more distant stars, just as a child in 
a swing observes near objects moving against the distant background of hills