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Polaris
Polaris ( Ursae Minoris, UMi, commonly the North Star or Pole Star) is the brightest star in the constellation Ursa Minor, and the 50th brightest star in the night sky. It is very close to the north celestial pole, making it the current northern pole star.
It is a multiple star, comprising the main star, UMi Aa, which is a supergiant; two smaller companions, UMi B and UMi Ab; and two distant components, UMi C and UMi D. UMi B was discovered in 1780 by William Herschel.
The revised Hipparcos parallax calculates the distance to Polaris at about 434 light-years (133 parsecs). Many recent papers derive distances up to 30% closer, particularly if the fundamental pulsation mode is assumed. It is especially important to derive an accurate model because Polaris is the closest Cepheid variable to Earth, so its physical parameters are critically important to the whole astronomical distance scale.〔
==History of observations==
Polaris in stellar catalogues and atlases
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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