The Northern Hemisphere summer occurs around the same point in the Earth’s orbit every year because this is where the Earth’s tilt aligns the north toward the position of the sun. After every 365-day year, the calendar year moves a quarter of a day away from the seasons. After four years, summer would start a day later. In less than four hundred years, within the lifespan of a civilization, the seasons would drift by three months. After eight hundred years, summer and winter would swap places completely.
