45.The source of Energy
A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Suns very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is librated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of year.
The nuclear energy is released at the Suns center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun to be reemitted at slightly longer wavelengths. This radiation , in its turn is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space without being absorbed further by solar atoms. A very small fraction of the Suns light and heat is emitted in such directions that after passing unhindered through interplanetary space, it hits the Earth.
英语语法:反身代词
英语语法:人称代词的用法
形容词及其用法
英语语法:人称代词之主、宾格的替换
英语语法:比较级形容词或副词 + than
英语语法:the + 最高级 + 比较范围
英语语法:冠词的位置
助动词do 的用法
英语语法:anyone/any one;no one/none;every/each的区别
few, little, a few, a little的区别
英语中可修饰比较级的词有哪些
英语语法:相互代词
短语动词的用法
英语语法:物主代词
形容词与副词的比较级
英语语法:零冠词的用法
英语语法:as + 形容词或副词原级 + as
英语语法:副词及其基本用法
助动词shall和will的用法
用形容词表示类别和整体
和more有关的词组语法讲解
英语语法:疑问代词
英语语法:none, few, some, any, one, ones的区别
助动词语法知识点
非谓语动词的用法
英语语法:many,much的区别
英语语法:冠词与形容词+名词结构
英语语法:双重所有格
接不定式作宾语的动词速记口诀
系动词的语法应用
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