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。
We shall hardly even touch the captivating problems of modern extragalactic astronomy. 甚至几乎不涉及现代河外天文学中吸引人的课题。
To study the star formation properties of galaxies is one of the major tasks of extragalactic astronomy. 星系的恒星形成性质的研究是目前河外天体物理学的热门研究领域。
Although the extragalactic space is a dangerous zone, you should also annihilate all the enemies on your journey. 虽然银河系外的空间是一个危险的地域, 但是，你也应该在你的旅程上消灭所有的敌人。
This Paper has Studied the observational parameters of 20 extragalactic H2O megamaser Sources. 研究了至今为止已发现的20个河外H2O超脉泽源的观测参数。
