When the Sun first became a main sequence star, it radiated only 70% of the current luminosity.
当太阳首次成为主序星，它的辐射只有当前光度的70％。
A star during most of its life is a main-sequence star, which consists of a core, radiative and convective zones, a photosphere, a chromosphere and a corona.
一颗恒星其生命的绝大部分处于主序星阶段，在这一阶段它包含一个核心、辐射区和对流区、光球层、色球层和日冕。
The star used to be like the sun, a "main sequence" star that burns hydrogen by nuclear fusion, producing helium.
这颗恒星曾和太阳一样，是颗“主序星”(“main sequence”)。它通过核聚变燃烧氢，从而产生氦。
The sun is thought to be about 5 billion years old and halfway through its lifetime as a "main sequence" star.
太阳现在的寿命大约是50亿年，作为一颗“主序”恒星，也只是过了生命的一半。
The greater the mass of such a star, the more quickly it will use its hydrogen fuel and the shorter it stays on the main sequence.
恒星的质量越大，它消耗氢燃料的速度也就越快，它在主序中停留的时间也就越短。
A heavy star at the upper end of the main sequence has a rather different later history.
在主序上端的大恒星具有很不相同的晚年史。
When a massive proto-star approaches the main sequence, its surface temperature is low and it can not ionize the ambient gas.
当一个大质量原星接近主星序时，它的表面温度是低的，因而不能电离周围的气体。
When a massive proto-star approaches the main sequence, its surface temperature is low and it can not ionize the ambient gas.
当一个大质量原星接近主星序时，它的表面温度是低的，因而不能电离周围的气体。
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