The aurora borealis is usually only seen in the north, but two weeks ago, the night sky was filled with shimmering curtains of pink and green light that could be seen as far away as the southern United States. People in Texas and Hawaii got out of their cars to admire and take photos.
The reason for this light show is something special The solar wind blows strongly—charged particles shoot out from the sun at incredible speeds. And there’s more to come as we reach the peak of the current solar cycle, a period of increased solar storms that occur every 11 years.
This is an example of what scientists call “weather space,” refers to the interaction between the sun and Earth. Not all consequences of space weather are good, and some are downright dangerous. But the physics behind it is pretty cool. Let’s check it out!
Blowing in the wind
You might think of the sun as a giant ball of fire, but it’s not. (Fire is a chemical reaction between oxygen and carbon.) The sun is actually a giant nuclear fusion reactor. In the core, protons collide with each other under extreme pressure. These protons stick together to form the nucleus of a helium atom, consisting of two protons and two neutrons. (Two of the protons decay into neutrons).
Illustration: Rhett Allain
But wait! The helium nucleus has a mass less than the four protons with which we started. That mass is not lost but it is converted into energy, according to Einstein’s famous equation E = mc2Where E is energy, I is the mass, and c is the speed of light. That last number is huge—light travels at 300,000 km/s and its magnitude is squared—which means that even a small loss of mass produces a LOT of energy. That’s why the sun is so hot, with a core temperature of up to 27 million degrees Fahrenheit. Yes, it’s pretty hot.
Under this extreme heat, gases in the outer part of the sun form plasma in which electrons are stripped from their atoms, leaving free charges (mainly electrons and protons) to magnify. around. Some of them move fast enough to escape the sun’s gravity. These ejected particles are what we call the “solar wind.”
You can see the impact of the solar wind as it hits the comet. Comets are basically big dirty snowballs that orbit the sun in long ellipses. As it approaches the sun, its icy object sublimates and turns into a gas. Some of these gases gain enough energy to become ionized (electrons are released from atoms), leaving behind a charged gas. Then, when the solar wind hits, it pushes this ionized gas away, forming a tail that can be tens of millions of miles long.
Fun fact: You might think the tail extending behind the comet looks like a jet streak, but it doesn’t! It extends away from the sun – essentially horizontally in the direction of the comet’s motion.
Why now?
But what makes the solar wind so active every 11 years? Well, like Earth, the sun has a magnetic field, but it is extremely unstable. Because the sun is not a solid object, different parts of it rotate at different speeds. This causes its magnetic field to twist and warp, and about every 11 years it actually reverses and reverses polarity. This last happened in 2013 and here we are in 2024.
Field lines from this motion can penetrate the surface, creating sunspots and amazing geysers of plasma called solar flares. Why does this happen? As charges move around, they can be repelled and attracted by a magnetic field. You can see this for yourself with some copper wire and a battery. If you place a wire near a stationary magnet and connect the two ends so that current flows through it, the wire will move. Check it out:
