Clearly, there were far more stars in the sky than the 6000 or so visible to our unaided eyes.

显然，天空中的我们肉眼可见的6000颗还多得多。

Interesting tidbit: It actually is visible to the unaided eye if you have very sharp eyesight and very dark skies.

如果你的视力很好，而且天空很暗，你就可以直接用肉眼看到它。

Neptune was the first planet to be discovered through mathematical predictions instead of being seen, as it is too faint to be observed with the unaided eye.

它还是首个由学测算而非观测发现的行，由于它太过暗淡，所以无法用肉眼观察到。

Galileo was the first to discover, or at least record, the fact that they were actually composed of many stars so close together our unaided eyes couldn't resolve them.

伽利略是第一个发现，或者至少记录了这样一个事：它们是由许多靠得很近的恒组成的，我们的肉眼无法分辨它们。

In order to find the magnifying power of the lens, you just divide the angle subtended by the virtual image by the angle subtended by your unaided eye.

为了求出镜片的放大倍率 ，只需用虚 像对角除以肉眼对角。

The original subtended angle is the subtended angle of the unaided eye – the angle between the center of the objective lens and the height of the real image.

原对角是肉眼的对角——物镜中心与像高度的夹角。

Although it is possible to see Uranus with the unaided eye in good viewing conditions, it was never recognized by ancient peoples as a planet because it was so dim and moved so slowly.

尽管可能在一个好天气里可以看肉眼看到天王，但是因为其亮度过暗和绕行缓慢，古代监测者并没有发现它是行。