40 FIRST YEAR COURSE IN GENERAL SCIENCE 



ter," because one fourth of the time from new moon to the 

 next new moon has passed. 



As the days go on, the half-disk grows to a whole disk or 

 full moon, and this in another week has diminished to a 

 half-disk called " third quarter." In about a week a small 

 crescent, the "old moon," is seen in the east before sunrise. 

 Then for a day or two the moon is again invisible because it 

 is in the same direction as the sun. When next seen, it is 

 a slender crescent in the western sky. 



The time from new moon to the next new moon is about 

 twenty-nine days. This was the period which the American 

 Indians used in reckoning time by "moons." 



33. The Time of Moonrise. The moon rises, on the 

 average, about fifty minutes later each day than the day 

 before. It has moved eastward from the place where it was 

 twenty-four hours before, and therefore the earth must turn 

 a little farther on its axis before the moon is visible at the 

 horizon. The full moon rises at the time of sunset, and 

 about two weeks later the new moon rises at sunrise but 

 is invisible to us. In a day or two, as it has moved 

 eastward, it rises an hour or so after sunrise, but it is 

 generally invisible to us while the sun is shining. People 

 rarely speak of the rising of the new moon, although 

 it actually rises at about the same time and place that the 

 sun does. 



34. The Moon's Surface. Looking at the moon with 

 the naked eye, we notice that some portions are less bright 

 than others. With the telescope it is found that these 

 darker portions are nearly level surfaces like plains. Around 

 them are brighter elevations or mountains, some of which 

 look like extinct volcanoes. In the summits of some of these 

 mountains there are deep depressions or craters with smaller 

 peaks in them. There is no air or water on the moon, so 

 far as men have been able to learn by any scientific 

 methods. No changes of importance have been observed 



