if an object reflects light toward the eye then that object can be seen & a moon is a kind of celestial object / celestial body ->  if the moon reflects light toward the eye then the moon can be seen  eyes are part of a human for seeing & there are humans on earth ->  humans on earth can see through their eyes  if the moon reflects light toward the eye then the moon can be seen & humans on earth can see through their eyes & the moon reflects sunlight towards the earth -> the moon can be seen by the humans on earth