Pole Star

The Pole Star is the current visible star that is closest to a line thru the north and south poles of the Earth that appears to be stationary, or nearly so, in the sky.

In our lifetime, around 2000 AD, the Pole Star is Polaris and is often called the North Star.

The Pole Star is useful for navigation.  It changes with time due to the wobble of the Earth.

A pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent position is close to one of the celestial poles, and which lies approximately directly overhead when viewed from the Earth's North Pole or South Pole. (A similar concept also applies to other planets.)

The term "the Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star. The south celestial pole currently lacks a bright star like Polaris to mark its position. At present, the naked-eye star nearest to this imaginary point is the faint Sigma Octantis, which is sometimes known as the South Star.

While other stars' apparent positions in the sky change throughout the night, as they appear to rotate around the celestial poles, pole stars' apparent positions remain essentially fixed. This makes them especially useful in celestial navigation: they are a dependable indicator of the direction toward the respective geographic pole, and their angle of elevation can also be used to determine latitude.

The identity of the pole stars gradually changes over time because the celestial poles exhibit a slow continuous drift through the star field. The primary reason for this is the precession of the Earth's rotational axis, which causes its orientation to change over time. If the stars were fixed in space, precession would cause the celestial poles to trace out imaginary circles on the celestial sphere approximately once every 26,000 years, passing close to different stars at different times. However, the stars themselves exhibit motion relative to each other, and this so-called proper motion is another cause of the apparent drift of pole stars.

The information between these lines came from Wikipedia on 29 Oct 2010.  It is not the work of the author of this website and is include here as useful information.

At the present time, the northern pole star, or North Star, is Polaris, which lies about three-quarters of a degree from the north celestial pole, at the end of the "bob" of the Little Dipper asterism in the constellation Ursa Minor. A common method of locating Polaris in the sky is to follow along the line of the so-called "pointer" stars, the two stars farthest from the "handle" of the Big Dipper.

Polaris is a moderately bright star with an apparent magnitude of 1.97 (variable) making it the brightest star in the Little Dipper. Its current declination is +89°15'50.8".

The North Star has historically been used for navigation, both to find the direction of north and to determine latitude. It always appears due north in the sky, and the angle it makes with respect to the horizon is equal to the latitude of the observer. The North Star is visible only in northern hemisphere skies and so cannot be used for navigation south of the equator.

Due to the precession of the equinoxes (as well as the stars' proper motions), the role of North Star passes from one star to another. Since the precession of the equinoxes is so slow, taking about 26,000 years to complete a cycle, a single star typically holds that title for many centuries.

Polaris' mean position (taking account of precession and proper motion) will reach a maximum declination of +89°32'23", so 1657" or 0.4603° from the celestial north pole, in February 2102. Its maximum apparent declination (taking account of nutation and aberration) will be +89°32'50.62", so 1629" or 0.4526° from the celestial north pole, on 24 March 2100.^[1]

Gamma Cephei (also known as Alrai, situated 45 light-years away) will become closer to the northern celestial pole than Polaris around AD 3000. Iota Cephei will become the pole star some time around AD 5200.

The brilliant Vega in the constellation Lyra is often touted as the best North Star (it fulfilled that role around 12000 BC and will do so again around the year AD 14000). However, it never comes closer than 5° to the pole.

When Polaris becomes the North Star again around 27800 AD, due to its proper motion it then will be farther away from the pole than it is now, while in 23600 BC it came closer to the pole.

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, and today it is invisible in light-polluted urban skies.