Galaxies星系
A galaxy is a huge family of stars, gas and dust held together by gravity. We live in a galaxy called the Milky Way.星系是由恒星、气体和尘埃组成的巨大“大家庭”，被引力聚在一起。我们住在一个叫银河系的星系里。
See it in 3D去看3D版Simple explanations简单说一说
The Milky Way银河系
Our galaxy has hundreds of billions of stars. The Sun is one of them, about 26,000 light-years from the center.我们的星系有几千亿颗恒星，太阳是其中之一，离银河系中心大约2.6万光年。
The band in the night sky夜空里的光带
On a very dark night you can see a pale band of light. That is the Milky Way seen from the inside.在非常黑的夜晚，你能看到一条淡淡的光带，那就是我们从里面看到的银河。
Our big neighbour我们的大邻居
The Andromeda galaxy is the closest big galaxy, about 2.5 million light-years away. In a very dark sky it looks like a faint smudge.仙女座星系是离我们最近的大星系，大约250万光年远。在非常黑的夜空里，它看起来像一小片模糊的光。
How many galaxies?有多少个星系？
Scientists think there are hundreds of billions of galaxies we could see. This number is an estimate, and it may change.科学家认为我们能观测到的星系有几千亿个。这个数字只是估计，以后可能会变。
Kinds of galaxies星系的种类
A bright center and curved arms full of young stars. The Milky Way is a spiral.有明亮的中心和弯弯的旋臂，旋臂里有很多年轻的恒星。银河系就是旋涡星系。
A smooth, glowing ball or oval. It has mostly older, redder stars.像一个光滑发亮的球或椭圆，里面多是年老偏红的恒星。
No clear shape. Some were pulled out of shape by their neighbours.没有固定的形状，有些是被邻居的引力拉歪的。
Computer-made models and drawings, not photos. Drag the 3D galaxy to turn it.电脑制作的模型和图画，不是照片。拖动3D星系可以转动它。
Where are we in the Milky Way?我们在银河系的什么位置？
Did you know?你知道吗？
- A light-year is how far light travels in one year, about 9.5 trillion kilometres.一光年是光走一年的距离，大约是9.5万亿公里。
- The Milky Way spins. The Sun takes about 230 million years to go around once.银河系在旋转，太阳绕一圈大约要2.3亿年。
Quick quiz小测验
What is a galaxy?星系是什么？
Gravity holds the stars, gas and dust of a galaxy together.引力把星系里的恒星、气体和尘埃聚在一起。
What is our galaxy called?我们的星系叫什么？
We live inside the Milky Way.我们就生活在银河系里面。
What shape is the Milky Way?银河系是什么形状？
Scientists think the Milky Way is a spiral. We map it from the inside, so pictures of it are artists’ drawings.科学家认为银河系是旋涡形的。我们是从里面测绘它的，所以见到的银河系图片都是画家画的。