Many objections can be raised to this picture of planetary nebula formation . 形成行星状星云的这一图像可能会引起许多异议。
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。
The filaments are expanding into space at a speed of roughly 5, 000 kilometers per second . 这些纤维状星云物质以每秒大约5000公里的速度向宇宙空间扩展。
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。
These unusual celestial bodies are composed of single or multiple nebulous patches, some nearly stellar in appearance . 这些异常天体，由单个或多个星云状斑组成，有的外形近于恒星。
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。
