They look like stars to the naked eye.

用肉眼看上去它们像星星。

《柯林斯英汉双解大词典》

Most stars are not visible to the naked eye.

大多数星星肉眼看不见。

《牛津词典》

What appears to the naked eye to be glowing is actually a superposition of different lines of distinct frequency. So, this is quantized.

出现在肉眼面前的光亮，事实上是频率不同的光线的叠加。所以，这是量子化的。

youdao

What appears to the naked eye to be just glowing is actually superposition of different lines of distinct frequency. So, you see, this is quantized.

出现在肉眼面前的光亮,事实上是波段不同的光线的叠加,所以，它是量子化的。

麻省理工公开课 - 固态化学导论课程节选

"The heat causes the wires to expand, imperceptibly to the naked eye, " Donovan said.

WSJ: Commuters warned: Summer heat may slow Metro-North

The proton aurora is invisible to the naked eye and has never been viewed from space.

BBC: Atmosphere Nasa

The samples revealed "no-see-um" gold, invisible to the naked eye but detectable via assay.

FORBES: Virtual Gold