CHARTING THE UNIVERSE 



could continue at unabated speed, fifty million years 

 would be required for it to reach the nearest star. 



That is to say, the star that is our nearest neigh- 

 bor in space lies about 18,000 times as far away from 

 us as the remotest member of the sun's planetary 

 family. The trip to Neptune bears the same. relation 

 to the trip to the nearest star that a brisk half hour's 

 walk here on the earth bears to the circumnavigation 

 of the globe. 



As to the stars that make up the main galaxies 

 that greet our eyes whenever we glance skyward, it 

 is futile to attempt to give a notion of their distances 

 in terms of mundane measurements. To say that our 

 mile-a-minute aeroplane would require a thousand 

 million years to reach a star of average distance, and 

 twenty or thirty billion years to come to the remoter 

 stars of the galaxy, conveys little meaning, since mil- 

 lions and billions, however glibly phrased, are incom- 

 prehensible terms. 



But whether or not such distances are compre- 

 hensible, they represent actual magnitudes with 

 which the astronomer, when he charts the heavens, 

 must deal as familiarly as the surveyor of land deals 

 with rods and miles. To make his figures a little 

 more manageable, the astronomer adopts a new unit 

 of measurement. He estimates stellar distances in 

 terms of "light-years;" the light-year being the dis- 

 tance that light, compassing 186,000 miles per sec- 

 ond, travels in 365 days. This distance the astrono- 

 mer's foot rule is almost six million million miles. 



The nearest star is at a distance of about four 

 light-years. The farthest stars revealed by the tele- 



31 



