THE EARTH'S PLACE IN THE UNIVERSE 21 



the North Star above the horizon is always the same as the 

 number of degrees of the observer from the equator. 



10. The Motion of the Stars, Apparent from Hour to Hour. 

 If we should watch the Dipper all night, we should find 

 that it, and all other stars in the vicinity, appear to move in 

 a circle around the Pole Star in a direction opposite to that 

 of the hands of a clock. Other stars, which we saw in the 

 east in the early evening, would rise higher, pass overhead, 

 and set in the west, all moving in the same direction as the 

 Dipper. At the end of a day (twenty-four hours), we should 

 see each group almost where it was at the beginning. This 

 apparent westward motion of the stars is due to the fact that 

 the earth is turning about its axis, always toward the east. 

 This motion of the earth makes the sun in the day, and the 

 moon and stars at night, seem to move toward the west. 



11. The Change in the Position of the Stars, Apparent 

 from Month to Month. If, instead of observing the posi- 

 tion of the stars from hour to hour, we watch them at the 

 same hour of the evening from month to month, we shall see 

 that a group of stars, as the Dipper or the Sickle or Orion, 

 has moved from its earlier position and that another constel- 

 lation has taken its place. 



People of ancient times reckoned the seasons by the posi- 

 tions of stars. In the same month of every year, a certain 

 constellation is seen in the east as soon 'as it is dark: Leo in 

 the spring, Scorpio in the early summer, and Taurus and 

 Orion in the fall and winter. This change of position, 

 which gives a different appearance to the sky at different 

 seasons, is due to the motion of the earth around the sun. 

 It moves eastward in its annual journey around the sun and 

 thus changes its position with relation to the stars. At 

 the end of a year, a given group will be found again where 

 it was seen at the beginning of the year. 



The rotation of the earth about its axis causes changes of 

 position which can be observed from hour to hour; the 



