April 17, 2012
NASA Satellite Captures Spectacular Solar Eruption
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A NASA satellite yesterday captured spectacular images and video of a massive solar flare erupting from the eastern side of the Sun.
The M1.7 (medium intensity) class solar “prominence eruption” produced a coronal mass ejection (CME) that was captured by NASA´s Solar Dynamics Observatory (SDO). The event occurred at 1:45 p.m. EDT on April 16, 2012.
The ejection, impressive as it was, was only a moderate event by astronomy standards. Such flares are measured on a letter scale and fall into three categories: C, M and X -- X is the strongest. Some of the strongest eruptions the Sun has produced have released as much energy as one billion megatons of TNT.
A solar prominence is a large, bright feature extending outward from the surface of the Sun. They are anchored to the Sun´s surface in the photosphere, and extend outward into the Sun´s outer atmosphere (the corona). A prominence forms over the period of a day typically, and stable prominences may persist in the corona for months at a time, looping hundreds of thousands of miles into space. Researchers are still studying how and why prominences are formed.
The looping material is plasma, a hot gas comprised of electrically charged hydrogen and helium. The prominence plasma flows along a tangled and twisted structure of magnetic fields generated by the Sun´s internal dynamo. An erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma.
CORONAL MASS EJECTION
The Sun´s corona is structured by strong magnetic fields. Where these fields are closed, often above groups of sunspots, the confined solar atmosphere can suddenly and violently release bubbles of gas and magnetic fields called coronal mass ejections (CMEs). Large CMEs can contain a billion tons of matter that can be accelerated to several million miles per hour in a massive explosion. Solar material streams out through the interplanetary medium, impacting any planet or spacecraft in its path. CMEs are often associated with flares but can occur independently as well.
While CMEs are often associated with solar flares that can impact Earth´s magnetosphere, causing electrical storms that disrupt satellites and other systems on Earth, and even pose threats to astronauts aboard the International Space Station (ISS), this event occurred on the eastern side of the Sun, and posed no threat to us here.
Solar flares only impact Earth when they occur on the side of the Sun facing Earth. Because flares are made of photons, they travel out directly from the flare site, so if we can see the flare, we can be impacted by it. High-speed solar wind streams that emit from solar coronal holes can form anywhere on the Sun and usually, only when they are close to the solar equator, can they produce strong enough winds to impact Earth as well.
Solar energetic particles, which can be formed at the front of CMEs, can also impact Earth, but only if they follow magnetic field lines that exist in the space between the Sun and Earth.
The Sun is nearing the peak of its current 11-year cycle of intense activity. The peak should occur in 2014-15, when the strongest solar events take place. However, the next few years could also produce some sizable flares, CMEs and prominences that, if occur on the Sun´s side facing us, could produce some damaging events here on Earth.
Image Caption: An eruption on April 16, 2012 was captured here by NASA's Solar Dynamics Observatory in the 304 Angstrom wavelength, which is typically colored in red. Credit: NASA/SDO/AIA