Polaris is the brightest star in Ursa Minor and can be found by extending a line from the Big Dipper. It is part of a trinary system and has been used by slaves in the Underground Railroad. Polaris is not precisely aligned with the celestial pole and will not always be the closest star to it. There is no true south pole star.
Polaris, also known as Polaris due to 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 rightmost stars in the Big Dipper “up” from the dipper’s “dipper” and locating a very bright star immediately on that line. Polaris has historically been used by slaves in the American South as they attempted to escape north via the Underground Railroad. Hence the popular 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 entire system lies between 400 and 460 light-years from Earth. Polaris’ name comes, of course, from its position as a pole star.
Polaris is a giant star containing five to six solar masses of material. It has a diameter of 60 solar radii and 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 appear to rotate in the night sky), but is in fact set 0.7° away from it, about 1 1/2 the width of the lunar disk. So you can’t rely on Polaris for highly accurate estimates of the direction of north unless you can take a time-lapse exposure of its movement across the sky. Due to variations in the Earth’s axis of rotation with respect to the plane of the elliptical, within a few tens of thousands of years Polaris will no longer be the closest star to the north celestial pole.
There is no true south pole star like Polaris for the north pole star, although the Southern Cross asterism points almost directly to the south celestial pole.
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