When the moon blocks the sun’s face during a total solar eclipse, the corona is revealed as a pearly-white halo around the sun. It is made of tenuous gases and is normally hiding in plain sight, overwhelmed by the bright light of the sun’s photosphere. The corona is the outer atmosphere of the sun. The brochure identifies key features in the sun’s atmosphere that you may observe during totality. Our 2017 eclipse brochure has a composite image of the sun on the back. But during an eclipse, the moon blocks out that intense light, allowing scientists to observe the much dimmer solar atmosphere. Under normal circumstances, the bright yellow surface of the sun, called the photosphere, is the only feature we can observe. Eclipse: Who? What? When? Where? and How?Ī total solar eclipse presents a rare opportunity to observe the corona and chromosphere, the two outer most layers of the sun’s atmosphere. ![]() ![]() The Alfvén waves that have now been observed provide an answer to both questions: as a result of enormous plasma speeds, these Alfvén waves produce enough energy to heat the corona and to propel solar wind. This raised the question of how nature can increase the speed of plasma to hundreds of km per second. When it reaches Earth's orbit, solar wind can reach speeds of 300 to 600 km per second. Moreover, resulting from the high temperature in the corona, the sun cannot retain plasma through solar gravity and the plasma flows away like solar wind. Until now, scientists were unable to provide an explanation for this phenomenon. This increase in temperature contradicts our intuitive expectation that temperature reduces the further we move away from the heat source. The photosphere of the sun - the sun's surface - has a temperature of approximately 6,000 C, while in the corona, the temperature rises to 2-3 million C. These transversal waves are called Alfvén waves when they occur on magnetic field lines loaded with plasma." This sideways (transversal) movement runs along the wire as a wave. If the wire is pulled off balance and then released, creating a catapult effect, the wire will move backwards and forwards as a result of the power of tension. ![]() Professor Goossens compares Alfvén waves to transversal waves on taut wires: "One might conceive of the magnetic field lines as taut wires loaded with mass (plasma). Plasma is glued to the magnetic field lines of these fields almost perfectly: when the plasma moves, the magnetic field lines move too and vice versa. The whole corona is filled with magnetic fields of various strengths and forms. Such hot, ionised gas is called plasma and has particular characteristics in the presence of magnetic fields. The gas of the corona is ionised as a result of the high temperatures. The corona is the outermost layer of the atmosphere of the sun, which we can only see as a ring of light during a total solar eclipse. The discovery of powerful Alfvén waves in the high atmosphere of the sun, which is now being reported in Nature, occurred with telescopes on board the Solar Dynamics Observatory - a NASA satellite for solar observation. ![]() Alfvén was awarded the Nobel Prize for Physics. His prediction was initially received with skepticism but its great significance was later recognised. The existence of these was predicted by the Swedish scientist Hannes Alfvén in 1942. Leuven and colleagues in the United States and Norway. This finding has been demonstrated by research conducted by Professor Marcel Goossens of the Centre for Plasma Astrophysics at K.U.
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