"No doubt of it," answered her father gravely. "At least she has tipped
over, so that in summer the North Pole is turned toward the sun, but in
winter it is turned away from the sun."

"Let me show you how I think it is," said Gerda eagerly. She was always
skillful at drawing pictures, and now she took the paper and pencil
which her father gave her, and talked as she worked. "This is the sun and
this is the earth's orbit," and she drew a circle in the center with a
great path around it.

"This is Mother Earth in the summer with the sun shining on her head at
the North Pole," and a grandmotherly-looking figure in a Rättvik costume
was quickly hung up on the line of the orbit, her head tipped toward the
sun.

"Here she is again in winter, with the sun shining on her feet at the
South Pole," and Gerda drew the figure on the opposite side of the orbit
with her head tipped away from the sun.

"That is exactly how it is," said her father. "But do you understand
that, when she is slowly moving round the sun, she is always tipped in
the same direction, with the North Pole pointing toward the north star;
so there comes a time, twice a year, when her head and her feet are both
equally distant from the sun, which shines on both alike?"

"No," said Gerda. "When does that happen?"

"It happens in March and September, when Mother Earth has travelled just
half the distance between summer and winter."