Some nebulae appear to be completely engulfed by exceedingly large molecular clouds . 有些气体星云似乎被极其巨大的分子云完全包围。
Good spectra of the spiral nebulas are difficult to obtain because of their extreme faintness . 旋涡星云因为非常暗，难以得到它们的清晰的光谱。
The general shape of the average nebula is that of a thin circular disk somewhat thick in the center . 星云最常见的形状是中间较厚边缘较薄的圆盘。
Precise thermodynamic equilibrium may never be achieved in a microscopic realm within gaseous nebulae . 精确的热动平衡永远不会在气体星云的一个微观范围内达到。
Planetary nebulae are a type of isolated gaseous nebulae possessing a fair degree of bilateral symmetry . 行星状星云是一类孤立的气体星云，具有相当程度的双侧对称性。
These sources are generally viewed in projection against radio nebulae representing the remnants of supernova outbursts . 这类源一般都投影在超星爆发残骸的射电星云上。
Such tumultuous, often visually spectacular, interstellar regions surrounding youthful stars are known as gaseous nebulae . 这种环绕着年轻星的动荡且常常是壮观的星际区域，叫做气体星云。
The great nebula is a cloud of glowing gas centered on four hot, blue stars located about 1, 500 light-years from the earth . 这个大星云是以离地球大约1500光年的四颗很热的蓝星为中心的发光气体云。
The temperature of the nebula in some places may never have risen high enough to evaporate pre-existing micron-sized interstellar grains . 星云中某些地方的温度可能从未升高到足以使原有的微米级大小的星际尘埃变成气体。
These calculations can be compared with the chemical analyses of meteorites in an attempt to ascertain the conditions in the nebula at the time of their formations . 这些计算可与陨星的化学分析相比较，从而推断在它们形成时星云中的条件。
