About a thousand open clusters are known.

目前已知的开放星团大约有一千多个。

Open clusters are loosely bound collections of dozens or thousands of stars, usually in an irregular shape.

开放星团是由数十或数千颗恒星松散结合而成的集合体，通常形状不规则。

Unlike open clusters, though, globulars are old.

不过，与开放星团不同的是，球状星团很古老。

Despite being larger than open clusters, globulars have more stars and are denser, which is one reason they live longer than open clusters.

尽管球状星团比开放星团大，但球状星团拥有更多的恒星，密度也更大，这也是它们比开放星团寿命更长的原因之一。

Like open clusters, the stars in them orbit every which way, like bees around a beehive.

和开放星团一样，其中的恒星也会绕着四周转，就像蜜蜂围着蜂巢转一样。

These stars can be bound together by their mutual gravity, forming an open cluster.

这些恒星可以通过相互的引力结合在一起，形成一个开放的星团。

Today you learned that open clusters contain hundreds or thousands of stars held together by gravity.

今天你了解到，开放星团包含数百或数千颗恒星，通过引力聚集在一起。

One of the most famous and beautiful open clusters in the sky is the Pleiades, about 500 light years from Earth.

天空中最著名、最美丽的开放星团之一是昴宿星团，大约距离地球 500 光年。

As someone who enjoys taking out a telescope and observing the sky, I'm a fan of open clusters, a few are favorite targets whenever I'm outside.

作为一个喜欢拿起望远镜观察天空的人，我是开放星团的迷弟，每当我外出时，有几个星团是我最喜欢的目标。

Most globulars are bigger than open clusters, with diameters perhaps a hundred light years across, though size is a bit hard to measure, since they don't really have an edge.

大多数球状星团都比开放星团大，直径大概有一百万光年，不过尺寸有点难以测量，因为它们并没有真正的边缘。