North Star
The
North Star is a title of the
star best suited for
navigation northwards. A candidate must be visible from Earth and
circumpolar to the
north celestial pole. The current one is
Polaris. It is the star at the end of the "handle" of the
Little Dipper asterism in the constellation
Ursa Minor.
The North Star has been historically used by explorers to determine their
latitude. At any point north of the
equator the angle from the horizon to the North Star (its altitude) is the same as the latitude from which that angle was taken. For example, the angle to the North Star for a person at 30° latitude will be about 30°.
Polaris has a
visual magnitude of 1.97 (second magnitude). In 3000 BC the faint star
Thuban in the
constellation Draco was the North Star. At magnitude 3.67 (fourth magnitude) it is only one-fifth as bright as Polaris. The first magnitude star
Vega will be the North Star by AD 14,000.
Currently, there is no
South Star as useful as Polaris; the faint star
σ Octantis is closest to the south celestial pole. However, the constellation
Crux, the Southern Cross, points towards the south pole.
*
Pole star
