Glossary term: 红巨星
Description: 红巨星是指表面温度相对较低，但直径比太阳等主序星大几十倍甚至上百倍的恒星。相对较低的温度使恒星表面呈现红色，而较大的直径则使恒星的亮度远超太阳。红巨星最初是主序星，即类似太阳的恒星，在其内核中通过核聚变将氢燃烧成氦。当这样一颗恒星的氢燃料耗尽时，它就会开始燃烧氦并合成更重的元素。这时，恒星会膨胀，其表面会在此过程中冷却下来，随着体积的增大，恒星会变得更加明亮。太阳将在数十亿年后进入红巨星阶段，届时地球上的生命很可能无法存活。红巨星的例子有，位于牧夫座的大角星和位于鲸鱼座的米拉星。红巨星的脉动（即恒星反复变大和变小的振荡）并不稳定，在脉动过程中，亮度会发生变化。米拉星就是一个极端的例子，它的亮度可以变化 1000 倍。在天文学家使用的光谱分类中，红巨星的光谱型大多属于M型，也有一些属于K型。红巨星和所谓的红超巨星类似，但质量更低。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
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