The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Magnetic North Pole. The North Pole is by definition the northernmost point on the Earth, lying antipodally to the South Pole. It defines geodetic latitude 90° North, as well as the direction of true north. At the North Pole all directions point south; all lines of longitude converge there, so its longitude can be defined as any degree value. No time zone has been assigned to the North Pole, so any time can be used as the local time. Along tight latitude circles, counterclockwise is east and clockwise is west. The North Pole is at the center of the Northern Hemisphere. The nearest land is usually said to be Kaffeklubben Island, off the northern coast of Greenland about 700 km (430 mi) away, though some perhaps semi-permanent gravel banks lie slightly closer. The nearest permanently inhabited place is Alert on Ellesmere Island, Canada, which is located 817 km (508 mi) from the Pole. While the South Pole lies on a continental land mass, the North Pole is located in the middle of the Arctic Ocean amid waters that are almost permanently covered with constantly shifting sea ice. The sea depth at the North Pole has been measured at 4,261 m (13,980 ft) by the Russian Mir submersible in 2007 and at 4,087 m (13,409 ft) by USS Nautilus in 1958. This makes it impractical to construct a permanent station at the North Pole (unlike the South Pole). However, the Soviet Union, and later Russia, constructed a number of manned drifting stations on a generally annual basis since 1937, some of which have passed over or very close to the Pole. Since 2002, a group of Russians have also annually established a private base, Barneo, close to the Pole. This operates for a few weeks during early spring. Studies in the 2000s predicted that the North Pole may become seasonally ice-free because of Arctic ice shrinkage, with timescales varying from 2016 to the late 21st century or later. Attempts to reach the North Pole began in the late 19th century, with the record for "Farthest North" being surpassed on numerous occasions. The first undisputed expedition to reach the North Pole was that of the airship Norge, which overflew the area in 1926 with 16 men on board, including expedition leader Roald Amundsen. Three prior expeditions – led by Frederick Cook (1908, land), Robert Peary (1909, land) and Richard E. Byrd (1926, aerial) – were once also accepted as having reached the Pole. However, in each case later analysis of expedition data has cast doubt upon the accuracy of their claims. The first verified individuals to reach the North Pole on foot was in 1948 by a 24-man Soviet party, part of Aleksandr Kuznetsov's Sever-2 expedition to the Arctic, who flew near to the Pole first before making the final trek to the Pole on foot. The first complete land expedition to reach the North Pole was in 1968 by Ralph Plaisted, Walt Pederson, Gerry Pitzl and Jean-Luc Bombardier, using snowmobiles and with air support.
Precise definition
The Earth's axis of rotation – and hence the position of the North Pole – was commonly believed to be fixed (relative to the surface of the Earth) until, in the 18th century, the mathematician Leonhard Euler predicted that the axis might "wobble" slightly. Around the beginning of the 20th century astronomers noticed a small apparent "variation of latitude", as determined for a fixed point on Earth from the observation of stars. Part of this variation could be attributed to a wandering of the Pole across the Earth's surface, by a range of a few metres. The wandering has several periodic components and an irregular component. The component with a period of about 435 days is identified with the eight-month wandering predicted by Euler and is now called the Chandler wobble after its discoverer. The exact point of intersection of the Earth's axis and the Earth's surface, at any given moment, is called the "instantaneous pole", but because of the "wobble" this cannot be used as a definition of a fixed North Pole (or South Pole) when metre-scale precision is required. It is desirable to tie the system of Earth coordinates (latitude, longitude, and elevations or orography) to fixed landforms. However, given plate tectonics and isostasy, there is no system in which all geographic features are fixed. Yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System.
Exploration
Pre-1900
As early as the 16th century, many prominent people correctly believed that the North Pole was in a sea, which in the 19th century was called the Polynya or Open Polar Sea. It was therefore hoped that passage could be found through ice floes at favorable times of the year. Several expeditions set out to find the way, generally with whaling ships, already commonly used in the cold northern latitudes. One of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827 reached latitude 82°45′ North. In 1871, the Polaris expedition, a U.S. attempt on the Pole led by Charles Francis Hall, ended in disaster. Another British Royal Navy attempt to get to the pole, part of the British Arctic Expedition, by Commander Albert H. Markham reached a then-record 83°20'26" North in May 1876 before turning back. An 1879–1881 expedition commanded by U.S. Navy officer George W. De Long ended tragically when their ship, the USS Jeannette, was crushed by ice. Over half the crew, including De Long, were lost.
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