2 : ; GENERAL SCIENCE 



The universe of which we are so small a part is made 

 up of many systems of heavenly bodies. These systems 

 probably consist, each of a central body like our sun, 

 around which revolve planets with their satellites, 

 and comets. Many of these systems are no doubt 

 much larger than our solar system, great and complex 

 though it seems to us. 



The Solar System so called from the Latin word 

 sol meaning sun consists of the sun at the center, the 

 planets and their satellites, the planetoids or asteroids, 

 and some comets. There are seven other planets be- 

 sides the earth revolving around the sun. They have no 

 light of their own like the true stars, but the light that 

 comes to us from them is a reflection of the light of the 

 sun. If we carefully observe the bright points of light 

 in the sky at night, we shall see that the true stars twinkle, 

 while the planets, when they are visible, give a steady 

 light like that of the moon. 



The Planets. - - The names of the planets comprising 

 the solar system, beginning with the one nearest the sun, 

 are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, 

 Uranus, and Neptune (Figure 1). Because of their mo- 

 tion around the sun the planets are continually chang- 

 ing their positions in relation to the other stars, whereas 

 the positions of the true stars do not appear to change 

 relatively to one another. It is due to this change of 

 position that they are called planets from the Greek 

 word meaning wanderer. The amount of time required 

 by the several planets to make a revolution about the 

 sun of course varies to a considerable degree, due to the 

 great difference in distance which they have to travel. 

 This difference in time of revolution accounts for their 

 change of position in relation to each other. 



