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The Stars That Make up the Constellation Ursa Minor

Easily washed out by the lights of modern society, the stars of the constellation Ursa Minor hold a greater significance than their dim appearance would suggest. Ursa Minor is a circumpolar constellation never completely setting in the northern night sky and quickly located using the more prominent stars of the constellations Ursa Major and Cassiopeia. Commonly referred to as the asterism known as the Little Dipper or Little Plough, the tail star of this constellation is Polaris, the current North Star. Polaris hasn't always been the North Star as the slow precession of the Earth gradually aligns other stars as the North Star. For example, the star Thuban in the constellation Draco served as the North Star for stargazers 5,000 years ago. This wobble is very slow and Polaris will continue to serve as the North Star for many more generations.
  1. Polaris (alpha UMi)

    • Seen as the tail star in Ursa Minor, Polaris is the brightest of the stars in Ursa Minor. This yellow supergiant is 2500 times more luminous than our sun but lies at a distance of 430 light years away, making it appear much dimmer than other stars in the night sky. Polaris varies in brightness, making it a Cepheid variable star, though the change in brightness is imperceptible to most casual observers. Polaris owes its significance to its position almost directly over the Earth's North Pole, making it a handy aid in navigation. Not only is the star used in the Northern Hemisphere to indicate North, but its elevation above the horizon correlates to the observer's latitude.

    Kochab (beta UMi)

    • One of the "Guardians of the Pole," Kochab is the second brightest star in Ursa Minor located at the far side of the constellation from Polaris. Along with Pherkad, Kochab appears to rotate around Polaris each night. Kochab is an orange giant 126 light years away and has exhausted its hydrogen fuel for fusion, resorting to reserves of helium for energy. Although Kochab is much closer than Polaris it appears slightly dimmer as a significant amount of its light is emitted as infrared, invisible to our eyes. Several thousand years ago Kochab was closer to the North Pole than Polaris, but never came as close to the North Pole as Polaris has currently reached.

    Pherkad (gamma UMi)

    • The other "Guardian of the Pole," Pherkad is a white giant 480 light years away that expended its hydrogen fuel for fusion some 100 million years ago. Using the Little Dipper asterism as a reference, Pherkad helps to form the far end of the box in the dipper with Kochab on top and Pherkad at the bottom. Appearing near Pherkad but not related to the star is Pherkad minor (11 UMi). In August 2009 a planet 10.5 times the mass of Jupiter was detected orbiting Pherkad minor.

    Other Stars

    • The remaining stars in Ursa Minor are quite faint and often require observation far from the lights of even small towns. Yildun (delta UMi), Urodelus (epsilon UMi), and Pharkadain (zeta UMi) all share nearly the same magnitude in brightness. Yildun is a white star in the handle of the Little Dipper closest to Polaris. Urodelus is a triple star system forming the next star in the handle and Pharkadain is a white star at the junction between the handle and the box. Alasco (eta UMi) is a yellow dwarf at the bottom of the box on the handle side.


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