nebula formation
星云形成
nebula observation
星云观测
nebula classification
星云分类
horsehead nebula
[天文]马头星云
orion nebula
猎户座星云；猎户星云
planetary nebula
行星状星云
reflection nebula
反射星云
emission nebula
发射星云
Extragalactic nebula is invisible to the naked eye.
我们用肉眼是看不到河外星系的。
A bit of mould is a pleiad of flowers;a nebula is an ant-hill of stars.
一粒霉菌是一簇美不胜收的花朵，一撮星云是无数天体的蚁聚。
As our nebula began to collapse under its own gravity and spin faster, a dense clump of matter formed in the center. It's called a protostar.
当我们的星云在自身重力作用下崩溃和更加快速地旋转时，星云中心形成了密集的物质块。这叫做原恒星。
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