A、Square. B、Triangular. C、Circular. D、Random. D讲座后面提到伽利略认为太阳黑子的形状经过太阳表面时会发生变化。可能某个特殊的太阳黑子是方的，然后变得更加不规则，再然后就变成另外一个样子了，因此D项“无规则的”为

We are going to start a study of sunspots today, and I think you’ll find it rather interesting. Now I’m going to assume that you know that sunspots, in the most basic terms, are dark spots on the Sun’s surface. That will do for now. The ancient Chinese were the first to record observations of sunspots as early as the year 165. When later European astronomers wrote about sunspots, they didn’t believe that the spots were actually on the Sun. That’s because of their belief at the time that the heavenly bodies, the Sun, Moon, Stars, and Planets, were perfect, without any flaws or blemishes. So the opinion was the spots were actually something else, like shadows of planets crossing the Sun’s face. And this was the thinking of European astronomers until the introduction of the telescope, which brings us to our old friend, Galileo. In the early 1600s, based on his observations of sunspots, Galileo proposed a new hypothesis. He pointed out that the shape of sunspots, well, the sunspots weren’t circular. If they were shadows of the planets, they would be circular, right? So that was a problem for the prevailing view. And he also noticed that the shape of the sunspots changed as they seemed to move across the Sun’s surface. Maybe a particular sunspot was sort of square, then later it would become more uneven, then later something else. So there is another problem with the shadow hypothesis, because the shape of a planet doesn’t change.
    What Galileo proposed was that sunspots were indeed a feature of the Sun, but he didn’t know what kind of feature. He proposed that they might be clouds in the atmosphere, the solar atmosphere, especially because they seemed to change shape and there was no predicting the changes, at least nothing Galileo could figure out. That random shape changing would be consistent with the spots being clouds. Over the next couple hundred years, a lot of hypotheses were tossed around. The spots were mountains or holes in the solar atmosphere through which the dark surface of the Sun could be seen. Then in 1843, an astronomer named Heinrich Schwa Trobe made an interesting claim. He had been watching the Sun every day that it was visible for 17 years, looking for evidence of a new planet. And he started keeping tracks of sunspots, mapping them, so he wouldn’t confuse them, so he wouldn’t confuse them with any potential new planet. In the end, there was no planet, but there was evidence that the number of sunspots increased and decreased in a pattern, a pattern that began repeating after 10 years, and that was a huge breakthrough.
22. Why didn’t European astronomers believe that there are sunspots ?
23. What is Galileo’s new hypothesis?
24. According to Galileo’s view, what was the shape of sunspots?
25. What is Heinrich Schwa’s finding?