For other uses of the words "Pole star" and "Polestar" see Polestar (disambiguation). Polestar may refer to one of the following. ...

A pole star is a visible star that is approximately aligned with the Earth's axis of rotation; that is, a star that lies in the direction pointed to by one of Earth's poles. There are potentially both north and south pole stars, but whether there is either depends on the current stellar configuration. The term the pole star usually refers to the star Polaris (colloquially referred-to as the "north star") which is the current northern pole star. Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ... The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ... Compass rose with north highlighted and at top North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the primary direction: north is used (explicitly or implicitly) to define all other directions; the (visual) top edges of maps usually correspond to the... A compass rose with South highlighted South is most commonly a noun, adjective, or adverb indicating direction or geography. ... Polaris or Cynosura (α UMi / α Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. ...

Pole stars change over time because stars exhibit a slow but distinct drift with respect to the Earth's axis. The primary reason for this is the precession of the Earth's rotational axis that causes its orientation to change over time. If the stars were fixed in space, precession would cause the position of a pole star to trace out an imaginary circle on the celestial sphere approximately once every 26,000 years. However, the stars themselves exhibit motion relative to each other (including the sun), and this so-called proper motion is another cause of the apparent drift of a pole star. Precession (also called gyroscopic precession) is the phenomenon by which the axis of a spinning object (e. ... In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of gigantic radius, concentric with the Earth. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real...

Pole stars are often used in celestial navigation. While other stars' positions change throughout the night, the pole stars' position in the sky does not. Therefore, it is a dependable indicator of the direction north. Celestial navigation, also known as astronavigation, is a position fixing technique that was the first system devised to help sailors locate themselves on a featureless ocean. ...

North pole

At the present time, Polaris is the pole star in the northern direction. Its 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. (ref: Jean Meeus, Mathematical Astronomy Morsels Ch.50; Willmann-Bell 1997) Polaris or Cynosura (α UMi / α Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. ... There are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... February is the second month of the year in the Gregorian Calendar. ... (Redirected from 2102) (21st century - 22nd century - 23rd century - other centuries) The twenty-second century comprises the years 2101 to 2200. ... Rotation (green), Precession (blue) and Nutation (red) of the Earth Nutation is a slight irregular motion (etymologically a nodding) in the axis of rotation of a largely axially symmetric object, such as a gyroscope or a planet. ... Aberration (Latin ab, from or away + errare, to wander), a deviation or wandering, especially used in the figurative sense as: In ethics, a deviation from the truth. ... March 24 is the 83rd day of the year in the Gregorian Calendar (84th in Leap years). ... 2100 is the last year of the 21st century. ...

South pole

Sigma Octantis is the closest star to the south celestial pole, but it is too faint to serve as a useful pole star. The Southern Cross constellation functions as an approximate southern pole constellation, by pointing to where a southern pole star should be. Some people travel to the equator in order to be able to see both Polaris and the Southern cross.this star has lots ofname like possy star as an example. Sigma Octantis (σ Oct / σ Octantis) is a magnitude 5. ... Crux, being Latin for cross, commonly known as the Southern Cross (in contrast to the Northern Cross), is the smallest of the 88 modern constellations, but nevertheless one of the most famous. ... The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ...

Other resources

See also

• astronomy
• North Star (Polaris Borealis)
• South Star (Polaris Australis)
• Lode Star
• celestial navigation