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In the early 1900s, astronomer Henrietta Swan Leavitt realized a class of stars called Cepheids pulsate, bright and dim, and every Cepheid that pulsates at the same rate has the same brightness.

1900 年代早期,天文学家 Henrietta Swan Leavitt 发现一系列名为造父变星,它有规律地变亮和变暗,并且每个造父变星以相同脉动就会有着相同亮度。

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