What is a solar flare?

We take a look at how these stellar explosions work.

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What is a solar flare?
All images courtesy NASA

The largest explosions in the solar system explained

A solar flare is a sudden, high-energy explosion of energy that extends out to the Sun’s corona, or outermost layer of the atmosphere. They are caused by a build-up of magnetic energy and occur in areas of strong magnetic fields around the equator of the Sun. The number and frequency of solar flares correlates to that of sunspots. These temporary dark spots on the surface of the Sun mark areas of intense magnetic activity. During the solar cycle, the number of sunspots increases and they concentrate near the equator. The more sunspots there are, the more solar flares there are.

Solar flares happen in three stages, with each stage lasting as short as a few seconds or as long as a few hours depending on the strength of the flare. During the precursor stage, the energy begins to release in the form of lower-wavelength, or soft, x-rays. Next, electrons, protons and ions accelerate nearly to the speed of light during the impulsive stage. Plasma rapidly heats to anywhere from 10 million to as much as 100 million degrees Kelvin during the impulsive phase. A flare not only results in a visible flash of light, it also emits radiation across the electromagnetic spectrum at other wavelengths. These include gamma rays, radio waves and x-rays. The final stage is decay, in which soft x-rays are once again the only emissions detected.

Solar flares are classified on a scale of A, B, C, M or X, with each classification being ten times stronger than the previous one. Within each letter classification there is also a one to nine scale; an A2 flare is twice as strong as an A1 flare, for example. This depends on their peak x-ray flux measurement as determined by the GOES (geostationary operational environmental satellite) system.

Effects on Earth

What is a solar flare?

The occurrence of a solar flare can have many different effects on Earth as well as on our space explorations. The hard x-rays emitted from a flare, as well as bursts of highly charged protons called proton storms, can do damage to both astronauts and spacecraft. Soft x-rays enter Earth’s ionosphere and can disrupt radio communications. Ultraviolet radiation and x-rays also cause the outer atmosphere to heat up, creating a drag on satellites in low Earth orbit and reducing their life span.

Corona mass ejections (CMEs) often occur along with solar flares. These ejections of a large amount of plasma can disturb the Earth’s entire magnetic field, known as a geomagnetic storm. Geomagnetic storms can damage satellites in high Earth orbit as well as power grids, leading to both communication and power outages.

Top five facts: Biggest solar flares

Raw footage of the solar flare emitted on 15/02/11

06/03/89 – Stength: X15.0
This flare caused a geomagnetic storm that ultimately knocked out power to the entire Canadian province of Quebec.

02/04/01 – X20.0
This flare was the largest one observed for decades until 2003. It was observed by the Yohkoh spacecraft, which orbited the Sun from 1991 to 2001.

28/10/03 – X17.2
This flare was observed by the SOHO (Solar and Heliospheric Observatory), a spacecraft currently orbiting the Sun. It had an associated coronal mass ejection.

04/11/03 – X28+
This solar flare was observed by NASA’s GOES satellite system and was the strongest solar flare recorded up until 2011. It was not directed directly at Earth, but did cause some radio blackouts.

15/02/11 – X2.2
This might not be the most powerful solar flare in recent history but the fact that it was directed at Earth meant that it threatened satellites and communications systems. Recorded by NASA’s Solar Dynamics Observatory, it was the largest solar flare seen in four years.

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