388 NATURE-STUDY REVIEW [14:9— Dec, 1918 



these agencies we know that every shining star is a great fiery sun, 

 and we may well believe that many of these suns have worlds 

 like our earth revolving about them, but a little world like ours 

 we could not see if it were revolving about even the nearest star. 



It is very hard for us to comprehend how far away from us is 

 the nearest star, but astronomers have been able to measure the 

 distance from us to many stars, and this distance is so great that 

 it can only, be reckoned at the rate at which light travels, which 

 is 186,400 miles per second or about six trillions of miles per 

 year and this distance is called a light-year. It requires light 

 about eight minutes to reach our earth from the sun, but it requires 

 more than four years for light to reach us from the nearest star. 

 Most of the stars are so far away that we cannot measure the dis- 

 tance from them to us, but it is interesting to know that the light 

 from the Pole Star which reaches our eyes in cloudless nights may 

 have started on its journey almost fifty years ago, while the light 

 that reaches us from the interesting little group of stars called the 

 Pleiades, may have started on its journey before Columbus started 

 on his great voyage. 



The stars seem always to us to keep their own places in the 

 heavens but they are all moving through space just as our sun 

 and its family are doing. However, the stars are so far away that 

 although one may move a million miles a day we would need to 

 make observations upon it for years to detect that it had moved 

 at all. We know that our sun and its planets are moving through 

 space at the rate of about 800 miles per minute. 



Stars also have the'r youth, middle age, and old age. When 

 they are young they are composed of thin gases and shine white 

 or blue; as they mature the gases condense and they shine yellow, 

 like our sun; when the gases become still more condensed they 

 shine red, like Betelgeuze in Orion, which is a very, very old star, 

 and after a time, more years than we can even think about, these 

 stars grow cold and dark and become invisible to us. The spectro- 

 scope shows us that there are many of these vast dead suns, with 

 their fires out, whirling through space. 



If any of us with especially good eyes were to travel from the 

 Northern to the Southern Polar region, we should be able to see 

 between six and seven thousand stars, although never more than 

 about two thousand at one time. With the aid of the telescope 

 about eight hundred thousand stars have been discovered. But 



