Polaris, also known as the North Star because of its proximity to the celestial pole, is the brightest star in the constellation Ursa Minor, the Little Bear or the Little Dipper. Polaris can be found by extending an imaginary line from the two farthest-right stars in the Big Dipper "upwards" from the "ladle" of the dipper, and locating a very bright star immediately on that line. Polaris was historically used by slaves in America's South attempting to escape to the North through the Underground Railroad. Hence the folk song, "Follow the Drinking Gourd". "Drinking gourd" refers to the Big Dipper.
Polaris, like many stars, is part of a trinary system that includes Polaris A, Polaris Ab, and Polaris B. The whole system is located between 400 and 460 light years from the Earth. The name of Polaris derives, of course, from its position as a polar star.
Polaris is a giant star containing between five and six solar masses of material. It is 60 solar radii in diameter and has a luminosity 2200 times greater than the Sun. Its surface temperature is 7700 K, significantly hotter than the Sun.
Polaris is not precisely aligned with the celestial pole (the axis around which stars in the night sky appear to rotate), but is in fact 0.7° removed from it, about 1 1/2 the width of the Moon's disc. So Polaris cannot be relied upon for extremely precise estimates of the direction of north unless a time-lapse exposure of its movement in the sky can be taken. Because of changes in the axis of the Earth's rotation relative to the plane of the elliptic, within a few tens of thousands of years Polaris will no longer be the star closest to the northern celestial pole.
There is no real Southern pole star like there is Polaris for the North pole star, although the Southern Cross asterism points almost directly to the Southern celestial pole.
