科学家认为地球上有生命已经有数百万年了，Scientists think that there has been life on earth for millions of years,

然而，我们还没有在其他行星上发现生命，However, we haven't found life on other planets yet,

为什么没有呢？地球是一颗行星，它绕着太阳转，另外八颗行星也围绕太阳运行 Why not?The Earth is a planet and it goes around the sun, Eight other planets also go around the sun,

他们没有一个有空气的环境，所以人和东西不能生长， None of them has an environment with air, so people and things cannot grow,

太阳及其行星被称为太阳系 The sun and its planets are called the solar system,

太阳系是我们银河系的一小部分， The solar system is a small part of our galaxy,

我们晚上看到的恒星是其他太阳系中的太阳，The stars we see at night are the suns in other solar systems,

我们的银河系中有2000多亿颗恒星，我们的太阳只是其中之一， There are more than 200 billion stars in our galaxy, called the Milky Way, and our sun is only one of them,

但是科学家发现了宇宙中的许多其他星系，But scientists have discovered many other galaxies in the universe,

它们离我们很远，它们的光已经传播了很多年到达我们这里， They are a long way away and their light has travelled for many years to reach us,

很难理解宇宙有多大， It is hard to understand how large the universe is,

科学家们已经发射了很多航天器去观察我们太阳系中的其他行星，一些航天器已经超越了太阳系。Scientists have sent lots of spacecraft to look at other planets in our solar system, and some spacecraft have gone beyond the solar system,

然而，还没有人在太空中发现任何生命。However, no one has discovered any life in space yet,

宇宙中有这么多恒星，我们是孤独的，还是太空中有生命？我们还不知道，With so many stars in the universe, are we alone, or is there life out there in space? We don't know yet,