Stars and the Sun恒星与太阳
Stars are giant balls of hot gas that shine. The Sun is the star closest to us.恒星是会发光的巨大热气球。太阳是离我们最近的恒星。
See it in 3D去看3D版Simple explanations简单说一说
What is a star?什么是恒星？
A star makes its own light and heat. Planets and moons do not.恒星自己发光发热，行星和卫星不会。
Why do other stars look tiny?为什么别的恒星看起来那么小？
They are very far away. The closest star after the Sun is about 4.2 light-years away. Its light takes 4.2 years to reach us.它们离我们非常远。除了太阳，最近的恒星大约在4.2光年之外，它的光要走4.2年才能到我们这儿。
Star colours恒星的颜色
Blue stars are the hottest. Yellow stars like the Sun are in the middle. Red stars are cooler.蓝色恒星最热，太阳这样的黄色恒星在中间，红色恒星更凉一些。
Why do stars twinkle?星星为什么会闪烁？
Starlight wobbles as it passes through Earth’s moving air.星光穿过地球上流动的空气时会抖动。
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Inside the Sun太阳里面是什么样？
Corona日冕 A thin, very hot outer layer. We can see it during a total solar eclipse.又薄又热的最外层。发生日全食的时候能看到它。
Surface表面 The glowing surface that makes sunlight. It is about 5,500 °C.会发光的表面，阳光就是从这里来的，大约5500摄氏度。
Bubbling layer翻滚层 Hot gas rises, cools, and sinks again, like bubbling soup.热气体升上来、变凉、又沉下去，像一锅冒泡的汤。
Slow-energy layer慢速传能层 Energy creeps outward through packed gas. The trip takes a very long time.能量在拥挤的气体里一点一点往外爬，要花很长很长的时间。
Core核心 The hottest part, about 15 million °C. The Sun makes its energy here.最热的地方，大约1500万摄氏度，太阳的能量就是在这里产生的。
The life of a Sun-like star像太阳一样的恒星的一生
Gas cloud气体云
A big cloud of gas and dust floats in space.太空里飘着一大团气体和尘埃云。
Young star年轻的恒星
Gravity squeezes the cloud. It heats up and starts to shine.引力把云团压紧，它变热并开始发光。
Steady star稳定的恒星
A star shines steadily for billions of years. Our Sun is about 4.6 billion years old, roughly halfway through this stage.恒星会稳定地发光几十亿年。太阳大约46亿岁，这个阶段已经过了大约一半。
Red giant红巨星
In about 5 billion years, the Sun will swell up and turn red.大约50亿年后，太阳会膨胀变大，颜色变红。
White dwarf白矮星
The star puffs off its outer layers. A small, hot core is left behind, and it slowly cools.恒星把外层吹散，留下一个小小的热核，它会慢慢变凉。
Did you know?你知道吗？
- The Sun is a medium-sized star. Some stars are much smaller and some are much bigger.太阳是一颗中等大小的恒星，有些恒星小得多，有些大得多。
- The Sun holds almost all of the weight of the Solar System, about 99.8%.整个太阳系几乎所有的重量都在太阳身上，大约占99.8%。
Quick quiz小测验
What is the Sun?太阳是什么？
The Sun is the star closest to us.太阳是离我们最近的一颗恒星。
Which stars are hotter?哪种恒星更热？
Blue stars are hotter than yellow stars like the Sun. Red stars are cooler.蓝色恒星比太阳这样的黄色恒星更热，红色恒星则更凉一些。
Why do stars twinkle?星星为什么会一闪一闪？
Starlight passes through moving air before it reaches our eyes.星光在到达我们的眼睛之前，要穿过流动的空气。