nebula GREGMAT

Extragalactic nebula is invisible to the naked eye.

我们用肉眼是看不到河外星系的。

You can see nebulae in the clear summer sky.

在晴朗的夏夜可以看到天上的星云。

A bit of mould is a pleiad of flowers;a nebula is an ant-hill of stars.

菌是簇美不胜收的花朵，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。