Later, the candles were blown out and an astronomer began to speak.

In addition to telescopes, astronomers have begun using other instruments to make observations.

But as they have looked longer and more sensitively, astronomers are beginning to find friendlier looking systems.

So when neutron stars were discovered, many astronomers began to believe that black holes must also exist.

In 1610, astronomers began using the telescope to make observations of sunspots and their motions.

About thirty years ago, astronomers began to realize that most of the matter in the universe wasn't the usual stuff you could see and touch.

Both amateur and professional astronomers have begun to use this technique.

But then, in the 1970s, astronomers began noticing something that didn't seem to fit with the laws of physics.

But two days ago astronomers began to realize that they might face a serious problem.

In the nineteenth century, astronomers began to take an interest in the historic records.