88 SEVENTEENTH CENTURY. FT. in. 



may be seen on the dark part of the moon when only one 

 quarter of it is bright and shining. Galileo discovered that 

 this curious light is a reflection from the earth ; for you must 

 know that we reflect the sun's light back to the moon just 

 in the same way as the moon does back to us, and at the 

 time when we see a new moon, the man in the moon (if 

 there were such a person) would see a large full earth, and 

 could wander about at night by earth-light as we do by moon- 

 light Look up at the new moon just about dusk in the 

 evening, and if it is a clear night you will most likely be 

 able to see a faint outline of the dark side of the moon, 

 which is caused by our earth-light shining upon it 



Jupiter's Moons. When Galileo had studied the moon 

 and gazed with intense delight on the myriads of tiny stars 

 in the Milky Way, he next turned his telescope to the planet 

 Jupiter. To his great surprise he saw three small shining 

 bodies like stars close to Jupiter, which were quite invisible 

 to the naked eye. Two of them were on the east side of 

 the planet and the other on the west. He waited eagerly 

 for the second night, to see if Jupiter would move away from 

 these stars, but he found them still together, only the two 

 stars which had been on the east side had now moved round 

 to the west, and they were nearer to each other than they 

 had been before. He was quite puzzled as to how this could 

 have happened, and watched and watched for many nights 

 whenever the clouds would allow him ; and at last, on the 

 fourth night after he had first seen them, he came to the 

 conclusion that all three stars were moving round and round 

 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 Galileo discovered Jupiter's four moons 

 in the year 1610. 



This was the first fact in favour of the Copernican theory 



