36 Galaxies Far, Far Away-Low

GALAXIES FAR, FAR AWAY FOCUS Question What can galaxies tell us about the universe?

遥远的星系焦点问题星系能告诉我们关于宇宙的什么?

What Is a Galaxy? If you look at a dark sky on a clear night, you will see thousands of stars. These stars make up a very small part of the billions of stars in our home galaxy, the Milky Way. Galaxies are enormous groups of stars, planets, dust and gas held together by gravity. Astronomers estimate that there are at least 100 billion galaxies in the universe. Some "tiny" galaxies contain only a few hundred or a few thousand stars. Giant galaxies have trillions of stars. Some galaxies are forming right now, but others are more than 13 billion years old. The light that reaches us from the most distant galaxies has traveled through space for billions of years.

什么是星系?如果你在一个晴朗的夜晚仰望黑暗的天空，你会看到成千上万的星星。 这些恒星只占我们所在星系银河系数十亿恒星中的很小一部分。 星系是由恒星、行星、尘埃和气体在引力作用下聚集在一起的巨大群体。 天文学家估计宇宙中至少有1000亿个星系。 一些“小”星系只包含几百或几千颗恒星。 巨大的星系有数万亿颗恒星。 一些星系现在正在形成，但其他的已经超过130亿年了。 来自最遥远星系的光已经在太空中穿行了数十亿年。

Exploring Galaxies In 1923, astronomer Edwin Hubble observed the Andromeda Nebula using the Hooker Telescope in California. He discovered that the Andromeda Nebula was not a nebula, but rather a galaxy made up of billions of stars. Before this discovery, our own Milky Way was the only known galaxy. Today, astronomers use even more powerful telescopes on land and in space to study galaxies.

1923年，天文学家埃德温·哈勃在加利福尼亚用胡克望远镜观测到了仙女座星云。 他发现仙女座星云不是一个星云，而是一个由数十亿颗恒星组成的星系。 在这个发现之前，我们的银河系是唯一已知的星系。 今天，天文学家在陆地和太空中使用更强大的望远镜来研究星系。

Looking Back in Time Astronomers describe distances in space in terms of light-years. One light-year is the distance light travels in one year. For example, the Andromeda galaxy is about 2.5 million light-years from Earth. It takes the light from Andromeda about 2.5 million years to travel to Earth! Light travels 300,000 kilometers every second, so a light- year is a very long distance. This means that when we look far into space, we are also looking back in time. When we look at Andromeda, we see what it looked like 2.5 million years ago. We won't know what it looks like today for another 2.5 million years! Think About It The Perseus galaxy cluster is 300 million light-years from Earth. Imagine that a creature living in the Perseus cluster is looking at Earth with a telescope. How might Earth look different compared to how it looks now?

天文学家用光年来描述空间中的距离。 一光年是光在一年里传播的距离。 例如，仙女座星系距离地球约250万光年。 来自仙女座的光需要大约250万年才能到达地球!光每秒传播30万公里，所以一光年是一个很长的距离。 这意味着，当我们遥望遥远的太空时，我们也在回顾过去。 当我们观察仙女座菌株时，我们看到的是250万年前的样子。 我们要再过250万年才能知道它今天是什么样子!英仙座星系团距离地球3亿光年。 想象一下，一个生活在英仙座星团中的生物正在用望远镜观察地球。 与现在相比，地球看起来会有什么不同?

Astronomers are not just interested in what galaxies look like now. They also want to learn how galaxies form and how they evolve, or change over time. One tool that looks out into space—and back in time—is the Hubble Space Telescope (HST). The HST orbits about 569 kilometers (354 mi.) above Earth's surface, and looks out into deep space. Astronomers use the HST to see objects that are more than 13 billion light-years away. The HST and other space telescopes can show how parts of the universe looked 13 billion years ago, shortly after it formed. Do You Know? Astronomers think that four billion years from now. gravity will cause the Milky Way galaxy and the Andromeda galaxy to merge into a single super galaxy.

天文学家们现在不仅仅对星系的样子感兴趣。 他们还想了解星系是如何形成的，以及它们是如何演变的，或随着时间的推移而变化的。 哈勃太空望远镜(HST)是一种可以观测太空和回溯时间的工具。 HST在离地球表面569公里(354英里)的轨道上运行，眺望着深空。 天文学家使用HST观测130亿光年以外的天体。 HST和其他太空望远镜可以显示130亿年前宇宙形成后不久的部分情况。 你知道吗?天文学家认为40亿年后。 引力会导致银河系和仙女座星系合并成一个超级星系。

Types of Galaxies Each galaxy is unique. Galaxies vary in size, shape, age, location, and how they move. One way astronomers classify galaxies is by their shape. There are three types of galaxies: spiral, elliptical, and irregular. Spiral galaxies have a bright center with arms of stars, dust, and gas spinning around the center. Spiral galaxies rotate through space around a central bulge of stars. Our home galaxy, the Milky Way, is a spiral galaxy. It contains roughly 400 billion stars.

星系的类型每个星系都是独一无二的。 星系在大小、形状、年龄、位置和运动方式上各不相同。 天文学家对星系进行分类的一种方法是它们的形状。 星系有三种类型:螺旋星系、椭圆星系和不规则星系。 螺旋星系有一个明亮的中心，由恒星、尘埃和气体组成的旋臂围绕中心旋转。 螺旋星系围绕着一个中央凸起的恒星在空间中旋转。 我们的母星系，银河系，是一个螺旋星系。 它包含大约4000亿颗恒星。