CH. XI. ASTRONOMICAL DISCOVERIES. 91 



Jupiter, as the moon goes round our earth. A few nights 

 later he found that there was a fourth star which went round 

 with them ; and so GaHleo discovered Jupiter's four moons 

 in the year 16 10. 



This was the first fact in favour of the Copernican theory 

 which ordinary people could understand. The planets had 

 till now been looked upon simply as lights in the sky moving 

 round the earth ; but now it could not be doubted that 

 Jupiter at least was something more than this, for he had a 

 system like our own, with four moons, to give him light by 

 night, instead of one. As usual there were a great number 

 of people who were alarmed at the fact that our little earth 

 should not be the central body in the heavens, and many 

 astronomers would not believe that Galileo had really seen 

 Jupiter's moons ; one was even so foolish as to refuse to 

 look through the telescope, for fear he should see them. 



Phases of Venus. — Galileo, however, now felt sure that 

 his new instrument would help him to read wonderful truths 

 in the beautiful universe of God, and he threw his whole heart 

 and soul into this grand study. It was not- long before he 

 discovered another proof that the planets move round the 

 sun and not round the earth. When he first saw the planet 

 Venus through the telescope she was round, but happening 

 to look at her one day when she was almost between the 

 earth and the sun, he saw her in the form of a crescent like a 

 new moon. Struck by this, he continued to observe her night 

 after night till she had made the whole journey round the sun, 

 and he proved to himself that she went through the same 

 changes as our moon, from a crescent shape to a full round 

 face. This was just what she would be expected to do if she 

 and we both travelled round the sun. Thus for the second 



