Arctic Circle and Antarctic Circle

As we move further north or south from the Equator, the annual variability of hours of daylight and darkness increases, until at the poles this reaches its extreme.

On the equatorial sides of the Arctic and Antarctic Circles, the Sun rises and sets once every 24 hours throughout the year. On the polar sides, however, this is not the case: between the vernal and autumnal equinoxes the Northern Hemisphere points towards the Sun, because of the Earth's position on its orbit, and there is perpetual daylight at the North Pole, with the Sun rising and falling towards the horizon but never sinking beneath it.

At the summer solstice in the Northern Hemisphere, the Sun is as far north as possible, and hence on this day all places within 23 degrees of the North Pole (and thus inside the Arctic Circle) have constant sunlight. At the South Pole, during this time, there is perpetual night.

At the northern winter solstice, conversely, the North Pole, being tilted away from the Sun, experiences perpetual night, while in the Southern Hemisphere the "midnight Sun" is visible throughout the south polar region.