But ultimately, the solar eclipse is the best chance scientists have to test them. It’s difficult to declare just one the most important. Probably all of those mechanisms scientists have thought up contribute to the corona’s extreme heat. “How that changes is tied to understanding how the corona is heated.” “We can look at how things change as we move from the surface up into the atmosphere,” Bryans says. (I will be in Wyoming with this team on the day of the eclipse and will be sharing more about how the experiments went.) There, the team will take images at a fast clip in both visual and infrared wavelengths to map how the corona changes as the moon moves across the sun. Bryans and his colleagues will be on a mountaintop near Casper, Wyo., in the path of totality. The formation of new coronal loops that connect to existing ones could dump in enough extra energy to heat the plasma up.ĭuring the solar eclipse, dozens of groups of scientists across the country will deploy telescopes equipped with filters to pick out polarized light, infrared light or those electron-deprived iron atoms in search of answers. Or maybe tiny explosions called nanoflares or jets called spicules carry energy away from the photosphere and into the corona. Maybe the magnetic anchors of those loops on the sun’s surface braid and twist the magnetic field above them, dumping in energy that is then continually radiated away like the heating element in a toaster. Maybe loops of magnetic field lines in the corona vibrate like guitar strings, heating things up, sort of like how a microwave oven heats food. “What we don’t understand is how that energy gets into the corona in the first place.” “We know there’s energy coming in, and it’s hard to get it out unless you get very hot,” says Amir Caspi of the Southwest Research Institute in Boulder, Colo. In this image from a total solar eclipse in 2008, red indicates iron that is missing 10 electrons, blue is iron missing 12 electrons and green is iron that’s missing 13 electrons - half of its original count. Scientists can use those electron-poor iron atoms to estimate how hot it is. The corona’s extreme heat strips electrons off of atoms of iron. Most of the ways that materials release energy - stripping electrons from atoms, accelerating those electrons so they release X-rays and ultraviolet particles of light - are already maxed out in the corona. Once the energy is there, the corona has a hard time radiating it away, so it builds up. Such extreme temperatures have something to do with the corona’s magnetic field, which is probably where all that energy is stored. These iron lines in the corona are still used to measure its temperature: The more electrons lost, the hotter the material in the corona ( SN Online: 6/16/17). But Grotrian realized that iron atoms stripped of several of their electrons by the heat were responsible. German astronomer Walter Grotrian observed spectral lines - the fingerprints of elements that show up when light is split into its component wavelengths - emitted by the corona during a total solar eclipse in 1869.Īstronomers at first assumed those lines were due to a new element they dubbed coronium. The corona’s diffuseness makes its heat even stranger - the most basic ways to heat a material rely on particles crashing into each other, but the corona is too tenuous for that to work.Īn eclipse first brought this abnormal arrangement to light. “It’s counterintuitive that as you move away from a heat source, it gets warmer,” Bryans says. Then in the corona, the temperature makes an abrupt jump to several million degrees. But the gas just above the photosphere is heated to about 10,000° C. The sun simmers at about 5,500° Celsius at its visible surface, the photosphere. 21 solar eclipse may bring scientists closer to settling that debate. “There are a bunch of different ideas about what’s going on there, but it’s still highly debated.” Data collected during the Aug. “It’s one of the longest unanswered questions in all of solar physics,” says Paul Bryans of the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, Colo.
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