888 Handbook of Nature-Study 



the stars which seem single to us are really double made up of two vast 

 suns swinging around a common center; and although they may be mil- 

 lions of miles apart, they are so far away that they seem to us as one star. 

 The telescope reveals many of these double stars and shows that they circle 

 around their orbits in various periods of time, the most rapid making the 

 circle in five years, another in sixteen years, another in forty-six years; 

 while there is at least one lazy pair which seems to require fully sixteen 

 hundred years to complete their circle. And the spectroscope has revealed 

 to us that many of the stars which seem single through the largest telescope 

 are really double, and some of these great suns race around each other in the 

 period of a few hours, which is a rate of speed we could hardly imagine. 



Astronomers have been able to measure the distance from us to many of 

 the stars, but when this distance is expressed in miles it is too much for us to 

 grasp. Thus, they have come to measure heavenly distance in terms of the 

 rate at which light travels, which is 186,400 miles per second or about six 

 trillions of miles per year ; this distance is called a light-year. Light reaches 

 us from the sun in about eight minutes, but it takes more than four years for 

 a ray to reach us from the nearest star. It adds new interest to the Pole- 

 star to know that the light which reaches our eyes left that star almost half 

 a century ago, and that the light we get from the Pleiades may have started 

 on its journey before America was discovered. Most of the stars are so far 

 away that we cannot measure the distance. 



Although the stars seem always to be in the same places, they are all 

 moving through space just as our sun and its family are doing ; but the stars 

 are so far away that, although one may move a million miles a day, it would 

 require many years of observation for us to detect that it moved at all. We 

 know the rate at which some of the stars are moving but have no idea of 

 their goal ; nor do we have any idea where our sun is dragging us at the rate 

 of nearly 800 miles per minute. It is thought that our sun and the other 

 suns are whirling around some greater center or centers; but if so, the 

 orbits are so many trillions of miles across that the suns all seem to be going 

 somewhere in a straight line, each attending strictly to its own business. 



Through the spectroscope we know something of the life of stars; we 

 know that when they are young they are composed of thin gases and shine 

 white or blue ; and as they grow older, they become more solid and shine 

 yellow, like our sun; and when older still, they grow red and are yet more 

 condensed, like Bethelguese in Orion, which is an aged sun and which will, 

 in time, grow cold and dark and invisible to us. The spectroscope reveals 

 many dark stars whirling through space vast, dead suns with their fires 

 extinguished, never to be lighted again unless, in its swift course, one of 

 them should hurl itself against another star with a fearful force which shall 

 shatter it into gaseous atoms, and these be thrown into fierce spiral whirl- 

 pools, from which it shall again be fashioned into a white-hot sun and 

 become a star in our sky. 



The scientists are coming to understand a little of how the stars are 

 made; for scattered through the skies are masses of misty light, called 

 nebulae, which means clouds; nebulae are vast gaseous bodies composed of 

 the stuff of which stars are made. Each nebula keeps its own special place 

 in the heavens just like a star, and is moving through space like a star. 

 The spectroscope shows that many of these shining, misty masses are made 

 up of glowing gases, largely hydrogen; and many are disk-shaped, twisted 

 into a spiral. There are grounds for believing that these spiral nebulae are 



