Source: NASA Goddard Space Flight Center, on Flickr
A solar flare is an enormously powerful eruption on the surface of the sun. It occurs around sunspots where powerful magnetic fields can suddenly release their magnetic energy. This eruption ejects billions of tons of mass into space, by way of huge particle clouds consisting of electrons, ions, and atoms. The energy output can be up to 6x1025
Joules, which is equivalent to millions of 100 megaton atomic bombs exploding at the same time!
Solar flares are often followed by a coronal mass ejection (CME). CMEs are similar to solar flares but they eject a much greater amount of mass.
The video below shows a solar flare with a CME, from June 7, 2011.
The ejected particles travel at millions of miles-per-hour. If they are headed straight towards earth they will typically reach it a day or two after being expelled from the sun's surface. However, if this happens the results can be disastrous.
The highly energetic particles created by intense solar flares or CMEs can disrupt communications and disable satellites, as well as knock out the electricity grid. They also pose a serious radiation hazard to astronauts in space, who aren't protected by the earth's atmosphere.
Long-range space travel, such as to Mars, would have to take into consideration the risk from solar flares and CMEs, in order to protect astronauts and sensitive electronic equipment from the radiation.
It is necessary to constantly observe the conditions on the sun to watch for these eruptions. It's a form of solar weather watching which must be taken very seriously. A sufficiently advanced warning will give us time to react and minimize the damage. For example, astronauts in space, with sufficient warning, can take up refuge inside their space craft or space station.
The Carrington Event of 1859 was caused by a massive solar flare or CME. It was so powerful that it created aurorae all around the world, even as far south as the Caribbean. Telegraph systems all over Europe and North America failed, and some caught fire. In some cases telegraph operators received electric shocks. Given the high level of telecommunication and electronic equipment existing today, a similar event would be catastrophic, perhaps causing 2 to 3 trillion dollars in damage worldwide. Therefore, it is of utmost importance to have the means to predict such an event in the future so that protective measures can be taken to minimize the damage caused.
Using a combination of detectors on earth and in space, the sun is being closely monitored for early warning signs of solar flares and CMEs pointed towards earth. The early warning signs include looking for high intensity x-rays and gamma rays, which are detectable well before the particle cloud reaches earth. This particle cloud poses the greatest threat.
High intensity x-rays and gamma rays are forms of electromagnetic radiation, which act as precursors. They travel at the speed of light, and as a result are detected much sooner than the (slower moving) particle cloud reaches earth; perhaps a day or more sooner. This allows some time for warnings to be issued which will help minimize the damage caused by the particle cloud.
The highly energetic particles from a solar flare or CME can produce stunning auroras in the earth's atmosphere. The energetic particles, upon approaching earth, are redirected by the earth's magnetic field towards the poles. Once there they collide with atoms in the atmosphere. This releases energy and creates the aurora light show that we see on earth. An example of an aurora is shown below.
via Brocken Inaglory
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