Now it is the Arctic Circle that has the 24-hour night and the Antarctic Circle that has the midnight Sun. At latitude 23° S, called the Tropic of Capricorn, the Sun passes through the zenith at noon. Days are longer in the Southern Hemisphere and shorter in the north. In the United States and Southern Europe, there may be only 9 or 10 hours of sunshine during the day. It is winter in the Northern Hemisphere and summer in the Southern Hemisphere. The Arctic Circle marks the southernmost latitude for which the day length is 24 hours on the day of the summer solstice. This is located at 90° – 23° = 67° N of Earth’s equator. If Earth were tilted a bit less, then the Arctic Circle would move farther North. In the limit at which Earth is not tilted at all (its axis is perpendicular to the ecliptic), the Tropic of Cancer would be right on Earth’s equator, and the Arctic Circle would simply be the North Pole. Suppose the tilt of Earth’s axis were tilted only 5°. What would be the effect on the seasons and the locations of the Tropic of Cancer and Arctic Circle? The Tropic of Cancer is at a latitude equal to Earth’s tilt, so in this case, it would be at 16° N latitude.

The Arctic Circle is one of the two polar circles, and the northernmost of the five major circles of latitude. It is shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circle marks the southernmost latitude for which at the December solstice (winter) the Sun does not rise and at the June solstice (summer) the Sun does not set. These phenomena ar The Arctic Circle is one of the two polar circles, and the northernmost of the five major circles of latitude. It is shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circle marks the southernmost latitude for which at the December solstice (winter) the Sun does not rise and at the June solstice (summer) the Sun does not set. These phenomena are referred to as polar night and midnight sun, respectively, and the closer to the pole one goes, the longer that situation persists. For example, in the Russian port city of Murmansk (three degrees north of the Arctic Circle) the Sun stays below the horizon for 20 days before and after the winter solstice, and above the horizon for 20 days before and after the summer solstice. The positions of the Arctic and Antarctic Circles vary slightly from year to year. Currently the Arctic Circle is 66°33′51.0″ north of the Equator. Its latitude depends on Earth's axial tilt, which fluctuates by a margin of some 2° over a 41,000-year period due to tidal forces resulting from the orbit of the Moon. Consequently, in… The Arctic Circle is the southernmost latitude in the Northern Hemisphere at which the centre of the Sun can remain continuously above or below the horizon for twenty-four hours; as a result, at least once each year at any location within the Arctic Circle the centre of the Sun is visible at local midnight, and at least once the centre is not visible at local noon. Directly on the Arctic Circle these events occur, in principle, exactly once per year: at the June and December solstices, respectively. However, because of atmospheric refraction and mirages, and also because the sun appears as a disk and not a point, part of the midnight sun is visible, on the night of the northern summer solstice, at a latitude of about 50 minutes of arc (′) (90 km (56 mi)) south of the Arctic Circle. Similarly, on the day of the northern winter solstice, part of the Sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level; those limits increase with elevation above sea level, although in mountainous regions there is often no direct view of the true horizon.

Midnight sun Midnight sun is a phenomenon that exists north of the Arctic Circle and south of the Antarctic Circle, where the Sun won't set at all and remains above the horizon at solar midnight. It means that the sun, on parts of the year, is visible the whole night long. The sun above the horizon at midnight in the Arctic or Antarctic summer. There are no people living permanently south of the Antarctic Circle (like Antarctica), but in Alaska, Canada, Norway, Greenland, Sweden, Finland, Russia, and some other countries north of the Arctic Circle, it is possible to watch the Midnight sun in the summer. The opposite of the Midnight sun is the Polar night, where the Sun won't rise at all and remains below the horizon even at solar noon.