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Science/Tech See other Science/Tech Articles Title: 'Sunspot cycle' causes changes in the corona during eclipse 'Sunspot cycle' causes changes in the corona during eclipse Two weeks ago, the path of a total solar eclipse passed over portions of Africa and Asia. This author had hoped to travel to Turkey for the event, but unfortunately his travel plans did not work out. From all accounts, the skies were clear over most of the entire path, and thus millions of people on our planet had the opportunity to witness this exceptionally unique phenomenon of nature. One of the major attractions of a total solar eclipse is the chance to see the corona, or outer atmosphere of the sun. While the gas in the corona is extremely hot -- upwards of one million degrees -- it is also extremely tenuous, and as a result the corona can only be seen during a total eclipse -- or, alternatively, with a device called a coronagraph, which creates artificial eclipses. Among the many viewers of last month's eclipse was a friend of this author from Iran who journeyed to Turkey, and who remarked that the corona in this eclipse appeared significantly different from the corona during the eclipse viewed from Iran in 1999. The difference in the corona's appearance between the two eclipses has much to do with the sunspot cycle. The term "sunspot cycle" refers to a phenomenon first noticed in the mid-19th Century by German astronomer Heinrich Schwabe, wherein the number of sunspots on the sun's "surface" increases and decreases over a period of approximately 11 years. During the times of sunspot maximum, or solar maximum, many dozens of sunspots, often gathered together into large groups, may be visible on the sun at any given time, whereas at sunspot minimum, or solar minimum, few if any sunspots are visible. Numerous other solar phenomena are also associated with the sunspot cycle. The corona, for example, is much quieter, especially over the sun's polar regions, at solar minimum than at solar maximum. At the 1999 eclipse, the sun was approaching solar maximum and thus the corona was full and active; since we are now near solar minimum the corona at last month's eclipse was less active and not much was visible over the sun's poles. Solar flares, which are massive and energetic eruptions of charged particles off the sun's "surface," and coronal mass ejections, which are eruptions of hot gas expelled through the corona, are stronger and more frequent during times of solar maximum. When the particles from such events encounter Earth, they can produce displays of the aurora, or northern lights (southern lights in the southern hemisphere), and they can also affect electronics aboard satellites, disrupt power grids here on Earth, play havoc with electronic communications, and produce other similar effects. There is also evidence that sunspot cycle-related phenomena can influence our weather. For example, a period during the late 17th and early 18th centuries during which almost no sunspots were visible coincides with a period of unusually cold temperatures in Europe that was known as the Little Ice Age. There is thus much practical interest in understanding the sunspot cycle and how it operates. About a century ago, the American astronomer George Ellery Hale discovered that sunspots are associated with magnetic fields on the sun, and in fact we now understand that sunspots are locations where magnetic fields extend through the sun's "surface." Because the sun, being made up of gas, does not rotate as a solid body, the magnetic fields become distorted and stretched due to the sun's rotation, and this in turn produces many of the sunspot-related phenomena we see during each sunspot cycle. We've learned, incidentally, that the magnetic polarity of the sun's northern and southern hemispheres reverses during each subsequent sunspot cycle, and thus the true sunspot cycle is actually 22 years. Earlier this year, a team of scientists led by Mausumi Dikpati at the National Center for Atmospheric Research in Boulder, Colo., announced they have developed a model that accurately portrays the times and strengths of the past eight sunspot cycles. Their model incorporates the physics associated with the magnetic fields near sunspots, together with circulation activity that is going on deep within the sun's interior. If this model is correct, it can in turn help us prepare for those occasions when the sun's activity affects us here on Earth. As in any scientific model, the proof of the pudding, so to speak, lies with its ability to make accurate predictions. Dikpati's team predicts that, based upon their model, the first sunspots of the next sunspot cycle will appear six to 12 months later than expected, i.e., we will first start seeing them in late 2007 or early 2008, as opposed to later this year or early in 2007 as the more conventional models predict. Furthermore, Dikpati's team predicts that the next sunspot maximum will be 30 to 50 percent stronger than the most recent one -- during which we witnessed some of the strongest solar flares ever seen and which produced, among other things, some very intense auroral displays. So, depending upon how accurate this new model might be, it appears rather possible that we may have some very interesting times coming up within the not-too-distant future.
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#1. To: Arete, Starwind, sourcery, markm0722, Phaedrus (#0)
barking dog ping
Time to dust off the Hallicrafters S-40A.
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