Associated with sunspots are coronal loops, loops of magnetic flux, upwelling from the solar interior. Sunspot activity will be more pronounced at solar maximum where the magnetic field is twisted to a maximum. The solar cycle spans approximately 11 years, from solar minimum to solar maximum, where the solar magnetic field is continually wound up (due to a differential rotation at the solar equator the equator rotates quicker than the poles). However during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity. During periods of quiet, the corona is more or less confined to the equatorial regions, with "coronal holes" covering the polar regions. The Corona is not always evenly distributed across the surface of the sun. The outer edges of the Sun's corona are constantly being transported away due to open magnetic flux generating the solar wind. The exact mechanism by which the corona is heated is still the subject of some debate, but likely possibilities include induction by the Sun's magnetic field and sonic pressure waves from below (the latter being less probable now that coronae are known to be present in early-type, highly magnetic stars). The corona is separated from the photosphere by the relatively shallow chromosphere. The corona is 10 −12 as dense as the photosphere, however, and so produces about one-millionth as much visible light. "Past hard X-ray instruments could not detect quiet active regions, and combination of new technologies enables us to investigate quiet active regions by hard X-rays for the first time," Ishikawa added.įOXSI is a collaboration between the US and e Japan Aerospace Exploration Agency.The Sun's corona is much hotter (by a factor of nearly 200) than the visible surface of the Sun: the photosphere's average temperature is 5800 kelvin compared to the corona's one to three million kelvin. "The key to this result is the sensitivity in hard X-ray measurements," said Shin-nosuke Ishikawa, a solar physicist at the Japan Aerospace Exploration Agency, or JAXA, and lead author on the study.
#SUN CORONA TEMPERATURE SERIES#
These kinds of temperatures are generally produced in solar flares, powerful bursts of energy.īut in this case, there was no observable solar flare, meaning the hot material was most likely produced by a series of solar flares so small that they were undetectable from Earth: nanoflares. The second flight of the FOXSI instrument - short for Focusing Optics X-ray Solar Imager - during its December 2014 flight on a suborbital sounding rocket detected a type of light called hard X-rays - whose wavelengths are much shorter than the light humans can see - which is a signature of extremely hot solar material. In a study published in the journal Nature Astronomy this week, the scientists reported that a NASA sounding rocket instrument spotted signatures of the long-sought small solar flares. One possible solution to the coronal heating problem is the constant eruption of tiny solar flares in the solar atmosphere, so small that they can not be directly detected. The cause of these counterintuitively high temperatures is an outstanding question in solar physics. "If you've got a stove and you take your hand farther away, you don't expect to feel hotter than when you were close," said one of the study authors Lindsay Glesener from University of Minnesota in the US.
The corona is hundreds to thousands of times hotter than the Sun's visible surface, the photosphere.īecause the Sun produces heat at its core, this runs counter to what one would initially expect: normally the layer closest to a source of heat, the Sun's surface, in this case, would have a higher temperature than the more distant atmosphere. Scientists have found that small solar flare could help explain why the Sun's atmosphere, the corona, is so much hotter than the surface.
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