第一章：欢迎来到宇宙 Welcome to the Universe

第一章：欢迎来到宇宙

Welcome to the Universe

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夜幕降临，抬头看看

Every night, when the Sun goes down and the sky turns dark, something magical happens.你有没有注意过，每当太阳公公下班回家，天空变成深蓝色，然后慢慢变成黑色的时候，会发生什么？没错！一颗一颗闪闪发光的小灯点亮了起来。Those little lights are called "stars" (星星, xīng xīng).

现在，我想邀请你做一件特别的事情。Right now, I want to invite you to do something special.今晚睡觉前，或者找个时间，走到窗边，或者最好走到室外，抬头看看天空。Go to your window tonight, or better yet, go outside, and look up at the sky.看看你能看到多少颗星星。数一数，猜一猜，然后用你的小脑袋想一想：Count them, guess how many, and think with your little brain:

这些亮亮的小点点到底在哪里？它们是什么东西做的？为什么它们会发光？But where are these little bright dots? What are they made of? Why do they glow?更重要的是，在所有这些闪闪发光的东西中间，有没有一颗特别的地方？More importantly, among all these twinkling things, is there one special place?

如果你正在思考这些问题，恭喜你！You guessed it!你已经迈出了成为小小天文学家（astronomer /əˈstrɒnəmər/ 天文学家）的第一步！天文学家就是那些专门研究星星、月亮、太阳和宇宙的人。An astronomer is a person who studies stars, moons, suns, and the universe.

什么是宇宙？

What is the Universe?

在我们开始探索星空之前，让我们先来回答一个超级重要的问题：What is the universe? 宇宙到底是什么？

如果我用最简单的话来说，宇宙就是everything that exists——所有存在的东西。The universe is everything that exists.所有的星星，所有的行星（planet /plænɪt/ 行星是像地球一样绕着星星转的大圆球），所有的气体，所有的尘埃，所有我们能看到的东西，所有我们看不到的东西，还有所有的空间——所有这些加在一起，就是我们的宇宙。

想象一下，你有一个超级超级大的盒子，大到比世界上所有的盒子加起来还要大无数倍。Imagine you have a super super big box, bigger than all the boxes in the world combined.这个盒子里装着所有的星星，所有的行星，所有的小行星，所有你能想到的东西。This box contains all the stars, all the planets, all the asteroids, everything you can imagine.而且，这个盒子本身也是宇宙的一部分！And this box itself is part of the universe!

宇宙有多大？

How Big is the Universe?

好，现在我们知道了什么是宇宙。But now we know what the universe is.接下来要问的问题可能更让你头晕：But the question that might make your head spin even more:

宇宙到底有多大？

How big is the universe?

让我告诉你，这个问题的答案，用你们小朋友的话说，就是“超级无敌大”！Very very very very BIG!

让我用一些你们能理解的例子来说明。

想象一座超级大的图书馆

Imagine a Super Big Library

你知道图书馆是什么样子的吧？里面有很多很多的书架，每个书架上有很多很多的书，每本书里有很多很多的字。You know what a library looks like, right? It has lots of bookshelves, each shelf has lots of books, each book has lots of words.

现在，让我们想象一座超级大的图书馆。Now let's imagine a super huge library.这座图书馆里的书比世界上所有图书馆的书加起来还要多，多到你数都数不清。In this library, there are more books than all the books in all the libraries in the world combined, so many you can't count them all.

猜猜看？宇宙里有多少颗星星？Guess what? How many stars are there in the universe?

答案是：比那座超级图书馆里所有的字还要多！

The answer: MORE than all the words in that super library!

天文学家们（就是那些用超级大望远镜看星星的科学家）估计，宇宙中大约有 2000亿到2万亿个星系（galaxy /ˈɡæləksi/ 星系就是由几十亿到几千亿颗星星组成的大家族）。Astronomers estimate that there are about 200 billion to 2 trillion galaxies in the universe.

一个星系有多少颗星星呢？How many stars are in one galaxy?

我们的太阳系所在的星系叫做银河系（Milky Way Galaxy）。Our galaxy is called the Milky Way Galaxy.银河系里大约有 1000亿到4000亿颗恒星（star /stɑːr/ 恒星就是像太阳一样自己能发光的大火球）。The Milky Way has about 100 billion to 400 billion stars.

让我把这两个数字乘起来：Multiply those two numbers together:

$$\text{星系数量} \times \text{每个星系的星星数量} \approx 2 \times 10^{11} \times 3 \times 10^{11} = 6 \times 10^{22}$$

也就是说，宇宙中可能有 7000万亿亿颗星星！That's 70 sextillion stars!写出来的话，就是 70,000,000,000,000,000,000,000!（这是70后面跟22个零！）

这个数字太大了，大到你的大脑可能都想象不出来。This number is so big that your brain probably can't even imagine it.没关系，这很正常。That's okay, that's normal.即使是世界上最聪明的科学家，一开始听到这个数字也会觉得难以理解。Even the smartest scientists in the world find this number hard to grasp at first.

地球在宇宙中的位置

Earth's Place in the Universe

好了，现在我们知道了宇宙超级大。Okay, now we know the universe is super big.那么，我们生活的地球，在宇宙中处于什么位置呢？So where is Earth, the planet we live on, in this enormous universe?

让我给你讲一个关于大小的故事。Let me tell you a story about size.

想象一下，你是一个小小的小蚂蚁。Imagine you are a tiny little ant.不是普通的小蚂蚁，而是一个缩小到比针尖还要小的小蚂蚁。Not just a tiny ant, but an ant shrunk down even smaller than a needle point.

现在，这只超级小蚂蚁要去找世界上最大的海洋——太平洋。Now this super tiny ant wants to find the Pacific Ocean, the biggest ocean in the world.

它来到太平洋边，蹲下来，用它小小的眼睛看着无边无际的大海。It comes to the Pacific Ocean, kneels down, and looks at the endless sea with its tiny eyes.

大海太大了，大到小蚂蚁看不到边。The ocean is so big that the tiny ant can't see the edge.

如果把这个故事里的“小蚂蚁”换成“地球”，把“太平洋”换成“宇宙”，就差不多是我们宇宙的真实情况了！

If we replace "tiny ant" with "Earth" and "Pacific Ocean" with "Universe," that's pretty much the real situation in our universe!

地球就像宇宙海洋中的一粒沙子。

Earth is like a grain of sand in the ocean of the universe.

想象一下，你捧起一把沙子，有多少粒？Imagine you scoop up a handful of sand, how many grains are there?可能几百粒，可能几千粒。Maybe hundreds, maybe thousands.

地球在宇宙中的位置，大概就是这样的感觉。Earth's place in the universe is something like that.

认识宇宙大家庭的成员

Meeting the Family Members of the Universe

好了，现在我们知道了宇宙很大，地球很小。Okay, now we know the universe is huge and Earth is small.接下来，让我们来认识一下宇宙大家庭的主要成员吧！Next, let's meet the main family members of the universe!

宇宙大家庭里有几个特别重要的成员，我们要记住它们的名字和特点。There are several very important members in the universe family, and we need to remember their names and characteristics.

1. 恒星——宇宙中的大火球

1. Stars – The Fire Balls of the Universe

恒星（star /stɑːr/ 恒星）是宇宙中最重要的成员之一。Stars are one of the most important members of the universe.简单来说，恒星就是那些自己能发光的天体。Simply put, stars are objects in space that can produce their own light.

我们每天看到的太阳，就是一颗恒星。The Sun we see every day is a star.它是一个超级超级大的大火球，大到可以装下130万个地球！It's a super super huge ball of fire, big enough to fit 1.3 million Earths inside!

你可能会问：如果太阳是一颗恒星，那为什么我们晚上看不到太阳呢？You might ask: If the Sun is a star, why can't we see the Sun at night?

好问题！Good question!因为地球在转。Because the Earth is spinning.当我们的地方转到背对太阳的时候，太阳就在我们的脚下那边，我们当然看不到它啦。When our part of Earth turns away from the Sun, the Sun is on the other side of the planet, so we can't see it.

天上那些闪闪发光的星星，绝大多数都是恒星——就像太阳一样，只不过离我们太远太远了，看起来才变成小小的光点。Most of the twinkling lights in the sky are stars – just like our Sun, but they're so far away that they look like tiny dots of light.

恒星的温度非常高。Stars are very very hot.我们的太阳表面温度大约是5500摄氏度，内部温度更高，高达1500万摄氏度！The Sun's surface temperature is about 5,500 degrees Celsius, and its interior is even hotter, reaching 15 million degrees Celsius!

天上的星星看起来都是白色的，对不对？Actually, if you look carefully at the stars in the sky, they have different colors!但如果你仔细看，有些星星偏蓝一点，有些星星偏黄一点，还有些星星偏红一点。Some stars appear more blue, some more yellow, and some more red.

你知道吗？星星的颜色和它的温度有关系！Did you know? The color of a star is related to its temperature!

蓝色的星星其实是最热的！Red stars are actually the coolest, and blue stars are the hottest!红色的星星反而是比较“冷静”的星星。Yellow stars like our Sun are in the middle.

2. 行星——恒星的孩子

2. Planets – The Children of Stars

行星（planet /plænɪt/ 行星是围绕恒星运行的大天体）是宇宙大家庭的另一个重要成员。Planets are another important member of the universe family.简单来说，行星就是那些围绕恒星运行、不会自己发光的天体。Simply put, planets are objects that orbit around stars and don't produce their own light.

我们的地球就是一颗行星。Our Earth is a planet.地球围绕太阳转，每转一圈是一年。Earth orbits the Sun, and one trip around is one year.

太阳系（Solar System /ˈsəʊlə ˈsɪstəm/ 太阳系就是太阳和所有围绕它转的东西）有八颗大行星，从离太阳最近到最远，依次是：The Solar System has eight major planets, from closest to farthest from the Sun:

1. 水星 Mercury /ˈmɜːkjʊri/ – 最小的行星，也是离太阳最近的 2. 金星 Venus /ˈviːnəs/ – 地球的“姐妹”，但没有水 3. 地球 Earth /ɜːθ/ – 我们可爱的家园！ 4. 火星 Mars /mɑːz/ – 红色的星球，人类正在研究能不能去那里 5. 木星 Jupiter /ˈdʒuːpɪtər/ – 最大的行星，大到能装下1300个地球！ 6. 土星 Saturn /ˈsætɜːn/ – 有漂亮的环 7. 天王星 Uranus /ˈjʊərənəs/ – 躺着转圈的行星 8. 海王星 Neptune /ˈneptjuːn/ – 最远的蓝色大行星

你可能听说过冥王星，它以前被认为是第九颗行星。You might have heard of Pluto, which used to be considered the ninth planet.但在2006年，天文学家们决定把它重新分类为“矮行星”。But in 2006, astronomers reclassified it as a "dwarf planet."所以，现在太阳系有八颗大行星。So now the Solar System has eight major planets.

3. 星系——星星的大城市

3. Galaxies – Big Cities of Stars

星系（galaxy /ˈɡæləksi/ 星系是由数十亿到数千亿颗恒星组成的庞大系统）就像星星们住的大城市。Galaxies are like big cities where stars live together.

前面我们提到了银河系，那就是我们太阳系所在的大城市。We mentioned the Milky Way earlier, and that's the big city where our Solar System is located.