Bellatrix - Bellatrix

The proper name of the star Gamma in Orion. It means "female warrior" in Latin. It is a bright pale blue star in the upper right corner of the Orion rectangle. This star and Betelgeuse are located on the shoulders of the hunter Orion. In 2000, its celestial position was 5 hours 25 minutes 08 seconds at right ascension and +6 degrees 21.0 minutes at declination, and it reaches its zenith at midnight around December 10 every year. Its apparent magnitude is 1.64 and its color index ( B - V ) is -0.22 (one of the indices that express the color of a celestial object, calculated by subtracting apparent magnitude V from blue magnitude B ). It is a giant star of spectral type B2Ⅲ. Its parallax is 13.4 arcmilliseconds and its distance from Earth is 243 light years. Its proper motion is 16 arcmilliseconds per year and its radial velocity is +18 kilometers per second. The surface temperature is 21,000 K (Kelvin), and the rotation speed v is v sin i = 59 km/s ( i is the tilt of the star's axis of rotation as seen from Earth). An interferometer has measured the star's angular diameter to be 0.71 arc milliseconds. Ultraviolet light has been observed.

[Atsuo Yamazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

オリオン座のγ(ガンマ)星の固有名。ラテン語で「女戦士」の意。オリオン座の長方形の右上の青白い輝星で、この恒星とベテルギウスが猟師オリオンの両肩にあたる位置にある。2000年の天球上の位置は、赤経5時25分08秒、赤緯プラス6度21.0分で、毎年12月10日ごろ真夜中に南中する。実視等級は1.64等、色指数（B－V）はマイナス0.22等（天体の色を表す指標の一つで、青色B等級から実視V等級を引いたもの）。スペクトル型B2Ⅲの巨星。視差は13.4ミリ秒角、地球からの距離は243光年。固有運動は16ミリ秒角／年、視線速度はプラス18キロメートル／秒。表面温度は2万1000K（ケルビン）、自転速度vはv sin i＝59キロメートル／秒（iは地球から見た星の自転軸傾斜角）。干渉計で星の角直径が測られており0.71ミリ秒角。紫外線が観測されている。

［山崎篤磨］

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