One is that stars aren't all the same intrinsic, physical brightness.

一是恒星的固有、物理亮度不尽相同。

That makes them good standard candles: objects whose intrinsic brightness, whose luminosity, is known.

它们的内在亮度是已知的。

Of course, some of the stuff I've explained we've learned through other means — the Earth is spinning, stars have different intrinsic brightnesses, and so on.

当然，我之前解释的一部分现象是通过其他途径获知的，比如地球自转、星星有不同的本征亮度等等。

If you have two stars that are the same intrinsic brightness — giving off the same amount of energy — and one is twice as far as the other, it will be one quarter as bright.

如果你有两颗本征亮度相同的恒星——释放出相同数量的能量——其中一颗与我们的距离是另一颗的两倍，那么它的亮度将是另一颗的四分之一。