Polar Star. It is a visible star that is aligned, at least approximately, with the Earth's Rotation Axis. That is, a star whose apparent position is close to one of the Celestial Poles and remains exactly in Zenit when observed from the North Pole or the South Pole. This concept also applies to other planets.
The term the Polar Star generally refers to Polaris, which is currently the northern polar star, also known as the North Star. Sigma Octantis (蟽 de Octante), which could be called the South Star because it is close to the South Celestial Pole, is not easily visible to the naked eye.
While the apparent position of the other stars changes during the night, rotating around the Celestial Poles , the apparent position of the polar stars remains fixed. This makes them especially useful in navigation, as their direction indicates their respective geographic pole, and their elevation angle can be used to determine latitude.
The identity of the polar star changes over time as the Celestial Poles slowly move through the star field. This is due to the Precession of the Equinoxes, which is a slow and gradual change in the orientation of the Earth's axis, causing the Celestial Poles to describe a circle in the star field, completing it approximately every 25776 years, passing through different stars. Another cause of the shift of polar stars is the movement of each star.
At present the northern polar star is Polaris, which is 0.75 degrees from the Celestial North Pole, at the end of the tail of the constellation Osa Menor.
Polaris is a moderately bright star with an Apparent Magnitude of 1.97, being the brightest star in the constellation Osa Menor.
Historically, the northern star has been used as a reference point for navigation, to determine the direction of the North and to determine the latitude, but only from the northern hemisphere, as the curvature of the earth prevents it from being seen from the southern hemisphere.
Past and future
Due to the Precession of the Equinoxes and the movement of each star, the role of North Star has passed from one star to another. Since the Precession of the Equinoxes is slow, a star holds this title for centuries.
Polaris will be at its closest point to the North celestial pole, 0.4526掳 in February 2102.
Gamma Cepheus, also known as Errai, located 45 light years from Earth, will be closer to the North Pole than Polaris and will become the North Star around 3000. Iota Cepheus will be around the year 5200.
Vega, the brightest star in the constellation Lira has been considered the best polar star (it played the role in 12000 BC and will play it again around 14000 BC), however, it has never come closer than 5掳 from the pole.
