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What is a solar flare?

Solar flares – an observed increased in brightness across the Sun’s surface – occur when charged particles travelling at high speed interact with solar plasma.

The acceleration of the electrons in the Sun is understood to be caused by magnetic reconnection – the magnetic field lines in the plasma break and reconnect, converting some of the energy of the magnetic field into thermal and kinetic energy.

Solar flares release a burst of energy equivalent to about a sixth of the Sun’s normal power output, and are often followed by a coronal mass ejection ­– in which huge amounts of charged particles and radiation are released from the Sun at very high speed.

Sometimes the ejected material simply rises as an arc above the Sun’s surface – a solar prominence. Occasionally, however, it’s blown out into the solar system. If it interacts with the Earth’s magnetic field, it can cause a geomagnetic storm.

The largest known such storm is the “Carrington Event”, which took place in 1859 and was observed by amateur astronomer Richard Carrington. Were a coronal mass ejection to hit the Earth today, it would likely cause widespread damage to electrical systems.

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