英语语法分析

Extragalactic nebula is invisible to the naked eye.

我们用肉眼是看不到河外星系的。

"Extragalactic nebula" is a former name for "galaxy".

“外星云”是“星系”的曾用名。

"The claim that it's extragalactic is kind of a guess," says Pravdo.

“这颗行星来自外星系的说法只是一种猜测，”普拉夫多说。