How do we know, for example, that the stars are really huge balls of fire like the Sun and very far away?

比如说，我们怎么知道恒星真的是像太阳一样巨大的火球，而且离我们很远呢？

youdao

Scientists know planets form out of the discs of material around young stars, but theory says the transition from dust disc to planetary system is rapid and few objects are caught during this phase.

科学家们知道行星是从年轻的恒星周围的物质盘中形成的，但是理论认为从尘埃盘到行星系统的转变非常快，人们很少见到在这一阶段的物体。

youdao

Did you know that nowhere else in all the Universes, and among the thousands of galaxies and millions of stars and planets, are the animals as badly treated as they are here on this Earth?

你知道，在所有的宇宙中，在成千上万的星系中，在数百万恒星和行星上，没有任何地方的动物能与地球上动物所受的不公待遇相比吗？

youdao

Our report earlier this month about the design of the American flag helped Anhthu Nguyen in Vietnam settle an argument: Now I know the meaning of the stars on the American flag and there are fifty stars.

VOA: special.2010.04.23