"It happens in March and September, when Mother Earth has travelled just half the distance between summer and winter."
"Oh, I see! This is where she would be;" and Gerda made two dots on the orbit, each half-way between the two grandmothers.
"Good," said her father. "Now when she is in that position, day and night, all over the earth, are each twelve hours long. We call them the 'Equinoxes.' It is a Latin word which means 'equal nights.'"
"In March and September do we have a day when it is twelve hours from sunrise to sunset, and twelve hours from sunset to sunrise?" questioned Gerda.
"Yes, and it is the same all over the earth the very same day," repeated Lieutenant Ekman. "If you will look in the almanac when you go home, you will see just which day it is."
Gerda studied her drawing for a few minutes in silence. "I think I understand it now," she said at last.
"It is easy to understand after a little study," her father told her; "but everyone has to see it for himself, just like the midnight sun.
"When the North Pole, or Fru Earth's head, is turned toward the sun we have the long summer days in Sweden. When it is turned away from the sun we have the long winter nights. The nearer we go to the pole, the longer days and nights we have. If we could be directly at the pole, we should have six months of daylight and six months of darkness every year."
"What did you say?" asked Birger, who came around the corner of the hut just in time to hear his father's last words.
"We were explaining how it is that the farther north we go in summer, the longer we can see the sun each day," said Gerda.