有着一个少于200年的轨道周期的彗星被称作“周期彗星”，其中最著名的可能要数哈雷彗星，它每76年围绕太阳运转一圈。
A comet with an orbital period of less than 200 years is called a "periodic comet", of which the best known is probably Halley's comet, which orbits the Sun every 76 years.
路易斯安那大学拉斐特分校的天文学家约翰·马泰塞和丹尼尔·惠特迈尔曾多次发表声明表示，基于长周期彗星运行轨道的不规则性，他们发现了该天体存在的证据。
Astronomers John Matese and Daniel Whitmire of the University of Louisiana at Lafayette repeatedly claimed to have evidence of its existence based on irregularities among long-period comets.
这种周期性轨道只是彗星生命中的一个阶段。
This kind of periodic orbit is only a phase in a comet's life.
现在我们继续讨论，谈谈轨道，特别是那些所谓的周期轨道彗星。
Let's continue our discussion now by talking about orbits, especially those of the so-called periodic-orbit comets.
天文学上把彗星按照它们的轨道周期分类。
Asteroids classify comets based on the durations of their orbits around the sun.
虽然天体撞击的毁灭性不容置疑，但是没有证据表明彗星导致了地球物种周期性的大灭绝。
While there’s little doubt about the destructive power of cosmic impacts, there is no evidence that comets have periodically caused mass extinctions on our planet.
科学家们已发显着显的迹象表明：太阳有一个小弟弟，它是一颗暗星，其偏爱轨道导致彗星群和流星雨周期性降落地球。
Scientists have found compelling evidence that the Sun has a baby brother, a dark star whose eccentric orbit is responsible for periodically showering the Earth with comets and meteorites.
红色的圈是一个类似彗星的长周期天体的轨道，注意一下这个天体和它的尾巴。
The red circle is the orbit of a long period object like a comet. Note the object and its tail.
科学家们已发现明显的迹象表明：太阳有一个小弟弟，它是一颗暗星，其偏心轨道导致彗星群和流星雨周期性降落地球。
Scientists have found compelling evidence that the Sun has a baby brother, a dark star whose eccentric orbit is responsible for periodically showering the Earth with comets and meteorites.
彗星电泳检测细胞DNA的损伤程度；流式细胞术分析细胞周期的变化。
Furthermore, DNA damage was measured by comet assay, and cell cycle was measured by flow cytometry.
彗星电泳检测细胞DNA的损伤程度；流式细胞术分析细胞周期的变化。
Furthermore, DNA damage was measured by comet assay, and cell cycle was measured by flow cytometry.
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