52 IN STARRY REALMS. 



or twenty thousand times less than its mean value. It 

 may be observed that a circle as large as the orbit of the 

 moon could be entirely included within the sun. This is 

 illustrated in Fig. 5. If we desire to find a convenient 

 standard of comparison between the distance of the moon 



Fig. 5. To compare the orbit of the moon with the size of the sun. 



and the size of the earth, let us think of a cord wrapped 

 ten times round the earth at the equator, this would be 

 long enough to extend from the earth to the moon. 



One of the earliest facts that any observer will notice, 

 is that the moon always turns the same face towards us. 

 The simplest observations suffice to give assurance on this 

 point. There are large and conspicuous marks on our 



