对长期积累的关于太阳黑子的观测资料进行统计分析，发现太阳黑子活动具有一系列周期性的变化规律，称为太阳黑子周期引。
在地球上，人们认为，表明太阳黑子周期最可靠的迹象之一是树木的生长速度，就像树干横截面上可见的年轮一样。
On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow, as seen in the rings visible in the cross sections of their trunks.
这是被称为太阳黑子周期。
很多号码在太阳黑子周期，这是他们发现的。
Many Numbers were based on the sunspot cycle, which they had discovered.
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