As the Earth travels around the Sun in its orbit, the north-south position of the Sun changes over the course of the year due to the changing orientation of the Earth's tilted rotation axes. The dates of maximum tilt of the Earth's equator correspond to the Summer Solstice and Winter Solstice, and the dates of zero tilt to the Spring or Vernal Equinox and Autumnal Equinox.
The first day of winter (the winter solstice) is the shortest day of the year and the first day of summer (the summer solstice) is the longest day of the year. In the United States, there are only about 9½ hours of daylight on the first day of winter and about 14½ hours of daylight on the first day of summer.
At the latitude of the Arctic Circle, the first day of summer is the only 24-hour day of total daylight. Further north toward the Pole, the number of 24-hour periods between sunrise and sunset increases. The ultimate long-day occurs at the North Pole where the Sun rises with the Vernal Equinox and finally sets again 189 days later with the Autumnal Equinox. Likewise, during the winter months, for regions north of the Arctic Circle, the sun will set for for at least one full day before rising again. Further north toward the Pole, the number of 24-hour periods before the sun rises again increases. At the North Pole, the sun will not rise again until the Vernal Equinox.
.jpg)
