Gravitational lensing tends to magnify distant sources and increase their apparent brightness, as rays of light become concentrated.

引力透镜往往会聚焦光束，放大远处的光源并且增加其视亮度。

That means if you can measure their period, you can determine how far away they are simply by measuring their apparent brightness.

这意味着如果你可以测量它们的周期，你就可以通过测量它们的表观亮度来确定它们离我们有多远。

Once we know how far it is, and we can measure its apparent brightness, we can figure out how luminous it is, how much light it's actually giving off, and its spectrum tells us its temperature.

一旦我们知道它有多远，我们就可以测量出它的表征亮度，算出它有多亮，它发出了多少光，而且它的光谱能告诉我们它的温度。