Sunspots and Solar StormsGalileo was the first to study dark spots on the Sun which we call "sunspots". They typically measure about 10,000 kilometers across, which makes them on the order of the size of the Earth. They often occur in groups, and come and go. At some times the Sun has hundreds of sunspots, while at other times it may have almost none. Individual spots may last from 1 to 100 days. A large group of spots typically lasts 50 days. The obvious question is "What causes the sunspots?". One observation that is part of the answer is that intense magnetic fields are associated with the sunspots, and that sunspots generally occur in pairs with the magnetic field coming out of one and into the other. If you examine the nature of the magnetic field of a bar magnet, you see that this implies that they are like opposite poles of a magnet. The magnetic fields in the sunspot areas are about 1000 times stronger than the magnetic fields of surrounding, undisturbed areas of the photosphere. Apparently, the sunspot pairs represent points where the internal magnetic field penetrates the surface at one spot and re-enters at the other. All the sunspot pairs in a given hemisphere, north or south, of the sun have the same magnetic polarity. That is, if the re-entry spot is on the side toward the direction of rotation of the Sun, then all the others in that hemisphere will have that orientation as well. At the same time the sunspots in the other hemisphere will have the opposite polarity. This shows that there is a high degree of long-range order in the magnetic field of the Sun, even though the pattern of sunspots seems random.
One model for the nature of the sunspots is that the intense magnetic fields inhibit or redirect the convective flow of the hot gases, which is normally toward the surface. Centuries of observations have shown that there is about a 11 year cycle between maxima of sunspot activity. The exception is a period of exceptionally low activity called the Maunder Minimum. References: |
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The Maunder Minimum of Sunspots"The Maunder Minimum is the name given to the period roughly from 1645 to 1715, when sunspots became exceedingly rare, as noted by solar observers of the time. It is named after the solar astronomer Edward W. Maunder (1851-1928) who discovered the dearth of sunspots during that period by studying records from those years. During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000-50,000 spots." The above text and image are from Wikipedia and you may freely use them under their conditions of use. |
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Sunspot CycleThe longterm data shown below is from NASA's Solar Science site. The periodic nature has persisted for hundreds of years. References: |
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