If astronomers could observe metallicity gradients in spiral galaxies billions of light-years away, we could see how steep the gradients were billions of years ago and thus how they change over time.

如果天文学家能够观测到十亿光年外的螺旋星云的金属丰度梯度，我们就可以知道亿万年之前的梯度有多大，因此也就可以知道它是如何随时间变化的。

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The mirror, in this case, is a vast blob of gas about 70,000 light-years away from the center of a spiral galaxy, where the quasar resides.

从这种情况看，这个大家伙实质上是来自70000光年之外的星系螺旋线（宇宙射线）的视像，也即是类星体所在之处。

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Around the dark core of an optical vortex, the energy flow carried by the light beam is like a spiral staircase, flowing in a clockwise or counterclockwise direction.

绕着光涡旋的黑暗中心，光束携带的能量流就像螺旋梯，沿着顺时针或者逆时针方向流动。

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Bank chief executives rationally have to pull back on lending in light of increased risks, Dimon says, a spiral effect the government is trying everything in its power to break.

FORBES: Banking