nebula GREGMAT

Extragalactic nebula is invisible to the naked eye.

们用肉眼是看不到河外系的。

You can see nebulae in the clear summer sky.

在晴朗的夏夜可以看到天上的云。

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.

当们的云在自身重力作用下崩溃和更加快速地旋转时，云中心形成了密集的物质块。这叫做原恒。