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The solar cycle or solar magnetic activity cycle is a nearly periodic 11-year change in the Sun's ... This cycle has been observed for centuries by changes in the Sun's appearance ... reversing the polarity of the polar fields (notice how the blue and yellow fields reverse in the ... "Centuries-old sketches solve sunspot mystery". As the Earth orbits the sun over the course of a year, different places ... June 21 in the Northern Hemisphere, occurs when the sun is farthest ... as they left no written record about why or even how it was built. ... The centuries-old holiday is observed by millions of people around the world and lasts 13 days.
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