北河三（Pollux）即双子座β星，意思是“拳术师”。全天第17亮星（夜晚最亮的是大犬座的天狼星），视星等1.14等，绝对星等1.09等，距离33.7光年。是颗K0IIIb型红巨星。光度为太阳的32倍。是距离我们最近的红巨星之一。 中文名北河三 外文名Pollux 别 称双子座β星 分 类恒星 质 量>2.30 ± 0.45 MJ 直 径8.3R 表面温度4,500 K 绝对星等1.09 自转周期38天 赤 经07h 45m 19.4s 赤 纬+28° 01' 35" 半长轴1.64 ± 0.27 离心率0.02 ± 0.03

Pollux, also known as Beta Geminorum (abbreviated β Geminorum, β Gem), is an orange-hued evolved giant star approximately 34 light-years from the Sun in the northern constellation of Gemini. It is the closest giant star to the Sun.

Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. In 2006, an extrasolar planet (designated Pollux b or β Gem b, later named Thestias) was confirmed to be orbiting it.