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Facts About Polaris

Historic songs and stories sing the praises of Polaris, the North Star, the brightest star in the constellation Ursa Minor and the asterism the Little Dipper. Some believe that Polaris was the infamous star of Bethlehem, the sign of Jesus Christ's birth, according to Biblical accounts. Slaves of the Civil War era followed the guidance of Polaris to seek freedom in Northern states, using codes and songs to pass on information to fellow slaves to "follow the Drinking Gourd." Because of its position in the sky, Polaris has served as a beacon in the night for those traveling through the dark.

Description
- Polaris, dim though it looks, actually outshines the sun.
  
  Astronomers designate Polaris as an F7 yellow supergiant star that dwarfs the sun. The North Star has a radius 45 times and a mass six times that of the sun. Polaris, with a surface temperature of 6,000 Kelvin, shines with the light and heat of 2,000 suns. The star appears faint in the night sky because it lies 430 light-years away, meaning the light from Polaris would have to travel 430 years to reach Earth. According to spectral classifications used by astronomers worldwide, a star designated "F" has a surface temperature between 6,000 and 7,500 Kelvin. A star's color reflects its spectral classification, which means F-type stars will appear yellowish. Polaris' subclass of F7 indicates that it is at the cooler end of F-type stars.
Luminosity
- To an observer on Earth, Polaris does not seem very bright. Astronomers classify the North Star as a second-magnitude star on the apparent magnitude scale; first-magnitude designations belong solely to the brightest stars in the sky, such as Sirius and Vega. Polaris is actually more luminous than many of the other stars in the sky, boasting an absolute magnitude of -3.59. The absolute magnitude of a star denotes its apparent brightness if the star lay only 32.6 light-years away, with negative designations brighter than positive ones. By comparison, the sun has a blinding apparent magnitude of -26.5, but if both the sun and Polaris lay at the same distance from Earth, Polaris would appear brighter.
North Star Status
- Polaris lies almost directly above the North Pole.
  
  If you draw an imaginary line through the center of Earth stretching from the south to the north, you would pierce the North Pole; this line specifies Earth's axis. Earth revolves in space around its axis. By extending the axis farther north into space, you would reach the North Celestial Pole, an extension of Earth's axis into space. Polaris almost exactly corresponds to this point, being off by a single degree. Polaris is circumpolar, meaning that it appears to revolve around the North Pole. Unlike other stars in the sky, including the sun, circumpolar stars never seem to rise or set. Astronomers predict that in 13,000 years, Polaris, due to the natural wavering of Earth's axis, will no longer represent the North Star; that honor will belong to an apparently brighter star in the sky --- Vega.
Relationship to Big and Little Dippers
- When facing north, you can detect Polaris without the aid of a telescope because the star lies in a relatively clear region of sky. One of the 88 recognized constellations in the sky, Ursa Minor, the Little Bear, houses the North Star. Polaris also forms the tip of the handle portion of the Little Dipper. Dubne and Merek, two stars that shape the outer side of the Big Dipper's bowl, point directly to the North Star. Neither the Little Dipper nor the Big Dipper is a constellation; instead, they are asterisms, familiar groupings of stars lying within bigger constellations.
Celestial Navigation
- A compass, unlike the North Star, may not always indicate true north.
  
  Many ancient cultures, including the Persians, used the position of the North Star to navigate the ocean. Sailors today still employ celestial navigation, using the position of stars --- the sun during the day and Polaris at night --- to find their way on the open seas. The Chinese and Europeans both invented the compass, which used Earth's magnetic field to designate north. This navigation device aided seafarers when neither the sun nor stars could steer vessels on cloudy days and misty nights. Compass failings caused ships to veer off course, resulting in shipwrecks and lost lives. Analysis of the causes for navigation disasters during the 15th century pointed to a flaw in compass design: the compass merely indicated magnetic north, which did not necessarily signify true north.
Mythology
- Polaris figures into the legends of many cultures, including the Norse myths.
  
  The Omaha Indians passed on a myth through the years detailing the wanderings of a chief's son and his subsequent finding of his way home with guidance from the "Star That Does Not Walk," meaning Polaris. The Scandinavians visualized Polaris as a sort of peg fastened at the center of the universe and around which all celestial objects --- representing the severed parts of enemies of the mythical Norse deities --- revolved. The ancient Arabs saw the North Star as an evil being, Al Kiblah, who killed a hero lain to rest among the stars of the Big Dipper. While the other stars revolve around the warrior, Polaris remains stationary and isolated from the rest of the sky.

Astronomy