North Pole

The North Pole, the northernmost point on the Earth, can be defined in four different ways. Only the first two definitions are commonly used. However it is defined, the North Pole lies in the Arctic Ocean.

The Geographic North Pole, also known as True North, is the northernmost point on the Earth as determined by the planet's rotation. It has a known fixed position, at latitude 90° North. The boundaries of Canada extend all the way to the Geographic North Pole. There is no land at this location, which is usually covered by sea ice.
The Magnetic North Pole is the northern point at which the geomagnetic field points vertically, i.e. the dip is 90°. This definition was proposed by Sir William Gilbert, a courtier of Queen Elizabeth I, in 1600 and is still used. Despite its name, it is a south magnetic pole, because the north pole (labelled N) of every other magnet is attracted to it, and opposite magnetic poles attract each other. Its location (in 2003) is 78�18' North, 104� West, near Ellef Ringness Island, one of the Queen Elizabeth Islands, in Canada.
The Geomagnetic North Pole is the pole of the Earth's geomagnetic field closest to true north. Like Magnetic North, it is a south magnetic pole. It is the centre of the region in the magnetosphere in which the Aurora Borealis can be seen. Its present location is 78�30' North, 69� West, near Thule in Greenland.
The Northern Pole of Inaccessibility is defined as the point in the Arctic farthest from any coastline, and is at 84�03' North, 174�51' West. It is of interest mainly to explorers and crackpot conspiracy theorists, and was first visited in 1927.

Astronomers define the north "geographic" pole of a planet in the solar system by the planetary pole that is in the same ecliptic hemisphere as the Earth's north pole. For the magnetic poles, their names are decided upon by the direction that their field lines emerge or enter the planet's crust. If they enter the same way as they do for Earth at the north pole, we call this the planet's north magnetic pole. Magnetic poles can flip flop from north to south and back again. The Earth's poles have done this repeatedly throughout history, and 500,000 years ago, the south magnetic pole was at the North Pole. It is thought that this occurs when the circulation of liquid nickel/iron in the Earth's outer core is disrupted and then reestablishes itself in the opposite direction. It is not known what causes these disruptions.

Saturn's moon Hyperion is the only object in the solar system that is known to lack a geographic north pole. It rotates chaotically due to a combination of its irregular shape and tidal influences from nearby moons.

The axial tilt of the planet Uranus is very nearly 90 degrees relative to the ecliptic plane, so that labelling one pole or the other to be the "north" pole is still a matter of some dispute. When a body's axial tilt is greater than 90 degrees, either one of two interpretations can be considered equally valid; the axis could be tilted greater than 90 degrees, or the labelling of the poles could be reversed (north becomes south) and the body considered to be rotating in a retrograde direction.

The projection of the north geographic pole onto the celestial sphere gives the north celestial pole.