That tube, researchers suspect, is the sun’s magnetic field. “You’d have to have something, a special tube maybe, that would transport energy from your fire.” She likens it to walking away from a campfire and feeling colder and colder until suddenly getting very hot. But the temperature at the Sun’s surface - the source of that energy - is a relatively balmy 5,500 degrees. The temperature in the corona is a blistering million or so degrees Celsius. Another boost arrived with the invention of powerful rockets in the early 1940s that could lob cameras above Earth’s atmosphere.Įven those early observations hinted at something very strange about the corona. But progress in understanding had to wait for researchers to apply lessons from quantum mechanics in the late 1930s, to correctly interpret the visible light seen from the ground. It’s thanks to eclipses, in fact, that people have known since antiquity that a white glow wreathed the Sun. To see the corona, you need an eclipse or a telescope equipped with a Sun-blocking disk. What little visible sunlight the corona reflects is vastly outshone by the Sun’s surface.
It emits most of its light at high-energy ultraviolet and X-ray wavelengths, which are blocked by Earth’s atmosphere. Winebarger, along with Steven Cranmer at the University of Colorado, summarized what we currently know about the corona in the 2019 Annual Review of Astronomy and Astrophysics. While society-disrupting flares are an extreme example, researchers hope that if they can better understand how energy gets into the corona, then we might be able to predict dangerous eruptions with enough warning to protect vital equipment. “As we become more of a space-based culture, understanding the Sun and how it interacts with the Earth is even more important.” “We’re very connected to these problems, even though it’s not necessarily something that’s going to change your life today,” says Amy Winebarger, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Ala. The largest flares from the corona can wreak havoc with power grids, wireless communication and satellites. That energy often affects Earth, with occasionally disastrous results. And perhaps most baffling of all, the corona is hundreds of times hotter than the Sun’s surface.įiguring out how this excess energy gets into the corona isn’t just an academic exercise. Some particles shoot out of the corona with so much energy that they approach the speed of light. The solar wind doesn’t slow down as it leaves the Sun - it speeds up. Events in the corona affect all of the Sun’s worlds, including Earth and the technological society that humans have built upon it.Īnd yet, despite roughly 80 years of study, much about the corona remains a mystery. Composed mostly of electrons and the bare nuclei of hydrogen and helium atoms, it is the launchpad for the solar wind - the stream of charged particles that escape the corona and wash over the planets, eventually petering out at the threshold to interstellar space. That glow is the solar corona, the Sun’s tenuous upper atmosphere of ionized gas. Daytime morphs into a 360-degree dusk, and where the Sun once hung a black hole punches through the sky, wreathed by a white ethereal glow. No matter what is found, however, the odds are good that on August 21, the world’s solar astronomers will be at least a little bit smarter at the end of the critical 90 minutes than they were before it.In the final moments before a total solar eclipse, the temperature drops, birds and insects sing, and the ambient light becomes otherworldly. This time around, there may or may not be a discovery as fundamental as what we now know as helium. The newly identified gas, appropriately, would take its name from Helios, the ancient Greek personification of the sun. It was during the Augeclipse, for example, that French astronomer Jules Janssen, studying the spectral lines in the fleetingly visible corona, noticed the signature of a buoyant gas that exists on Earth but had not yet been discovered here. It is impossible to say now what discoveries might be made during the fleeting 90 minutes of eclipse totality, but history offers precedent. The spiky corona of five years ago will likely give way to a quieter one, with a great deal of complex activity near the solar equator but much less in the north and south hemispheres. At the moment, the sun is in a solar minimum phase. In 2012, the sun was going through one of the phases known as the solar maximum - when it is especially active and turbulent. The 2017 spectacle will also afford an opportunity to compare the current appearance of the corona to the way it looked during the 2012 eclipse - and the difference should be significant.
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