Solar Flare: Definition & Effects

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson will explain what a solar flare is, how we think they form, and describe the effects of a particularly large solar flare on the Earth. A short quiz will follow.

What is a Solar Flare?

Sometimes growing up it might have seemed like your brother was nothing but a big ball of gas, but the Sun really is one. And just like your brother, when there's a big supply of gas, the results can be pretty dramatic... if not quite so smelly.

With all the churning and heat inside the belly of the Sun, it's not surprising when there's an occasional burp. This is essentially what a solar flare is. A solar flare is a sudden and hard to predict explosion in the layers of the Sun that causes streams of charged particles to be ejected. They tend to happen more when the Sun's activity is greater. Sometimes they can also lead to a coronal mass ejection where large amounts of physical material from the sun is flung out into space... and occasionally towards the Earth.

A Solar Flare
A Solar Flare

It only takes a few minutes for a solar flare to heat material by millions of degrees, creating an explosion equivalent to a billion megatons of TNT. Flares can release energy across the whole of the electromagnetic spectrum, but especially x-rays and gamma rays, and they produce large quantities of energetic charged particles (protons and electrons). It takes 8 minutes for the radiation itself to reach the Earth, but 2-4 days for any charged particles (the most dangerous part) to get here.

The biggest solar flare (and coronal mass ejection) in recorded history happened in 1859, and its effects were quite dramatic. Telegraph systems all across Europe and North America failed, with some operators being electrocuted, and the Aurora Borealis was visible from as far south as the Caribbean. But how exactly do they happen?

Formation of Solar Flares

We might know how the body produces its many, disgusting eruptions. But the Sun is not so obvious. The exact process by which solar flares form is still debated, though scientists do have some ideas. They noticed that they always occur near sunspots, and often near the boundary between two magnetic fields pointing in opposite directions. So clearly it has something to do with a release of energy stored in those magnetic fields.

Formation of a Coronal Mass Ejection
Formation of a Coronal Mass Ejection

One way of imagining it is to picture the Sun's magnetic field as a series of rubber bands wrapped from pole to pole. Since the Sun spins, the magnetic field lines become wrapped around the Sun, getting tighter and tighter. Eventually, just like rubber bands, the stress becomes too much and the rubber bands 'snap'! And just like how elastic stores elastic potential energy, magnetic fields store magnetic potential energy, and when the field lines snap, that energy is released! The place where the 'rubber bands' snap, is where the solar flare happens.

Formation of Solar Flares
Formation of Solar Flares

The problem with this description is that we have no proof that it is accurate. It might be a long time until we know for sure.

Effects of Solar Flares

Run! Panic! That seems to be the message the news media sends us when there's a chance of the particles from a solar flare hitting the Earth. But most either miss us, or are pretty minor.

The magnetosphere protects us from some solar radiation, pushing it to the poles.
The magnetosphere protects us from some solar radiation, pushing it to the poles.

There is one part the media gets right: one day, a particularly big solar flare really could cause major damage. A solar flare amounts to a huge electromagnetic pulse -- an enormous burst of high energy waves and charged particles. And in the case of an unusually large flare, that could be bad news for all the electronics we rely upon every day.

Satellites would be one of the first things affected, the same satellites we use for GPS tracking, weather reports, communication and satellite television. These satellites would all be at risk. They could shut down for a time, their electronics could become damaged, and due to more charged particles in the Earth's upper atmosphere, drag could cause their orbits to decay and send them crashing into the ocean!

The International Space Station (like all satellites) could be at risk!
The International Space Station (like all satellites) could be at risk!

The power grid might also be in trouble. The extra charge in the atmosphere could lead to a charge build up on power lines, blowing out both power stations and transformers. Without power, refrigeration, water treatment and sewage treatment would all be at risk.

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