When you look up at the sky on a sunny day, the Sun might seem like a bright spot, unchanging in the sky. But the Sun is a complex, dynamic celestial body, wrapped in electrical currents and magnetic fields that constantly move and tangle as it rotates. At times the Sun’s surface is very active, casting out powerful bursts of plasma called coronal mass ejections, while at other times it is calmer.
I’m a solar physicist who has spent over a decade researching the Sun. Its movement and activity is directly linked to conditions on Earth: Solar flares and ejections can cause space weather that produces beautiful Northern lights but threatens satellites. This activity follows a roughly 11-year-long cycle, and learning about this cycle helps researchers predict future space weather.
Inside the Sun
The Sun is a star composed of plasma: a hot, ionized gas. The plasma acts as an electrically conductive fluid, and generates large-scale magnetic fields that encircle the Sun.
The Sun is composed of several layers, all made up of a plasma that’s about 70% hydrogen and 28% helium by mass.
The Sun has a solid core at its center and a dense layer outside the core, where particles of light bounce around, transferring energy outwards. Beyond that layer is a thin line called the tachocline that separates those inner layers from the outer layer. This outer zone is cooler and less dense, allowing plasma to move around.
The Sun’s interior is made up of several layers.
Kelvinsong/Wikimedia Commons, CC BY-SA
Inside the core, particles collide and release incredible amounts of energy, which radiate out from the Sun in the form of light – a process called nuclear fusion. The light travels outward towards the radiative zone outside the core, before reaching the tachocline.
At the outer layer of the Sun above the tachocline, called the convective zone, the hot plasma travels from deep in the Sun to its surface. As it moves, the plasma cools and contracts, causing it to sink back down. This cyclic process is called convection.
Explaining sunspots, solar cycle and solar dynamo.
The Sun is constantly generating magnetic fields that grow and twist below its surface. Two processes control these magnetic fields by moving the electric charges around in the plasma. One is convection, and the other is the Sun’s rotation.
Scientists think that together, these two processes are ultimately responsible for the Sun’s magnetic activity cycle, during which the Sun shifts from an organized to a less organized magnetic field arrangement. The entire cycle, called the Schwabe Cycle, takes roughly 11 years. Over the course of two Schwabe cycles, the Sun’s magnetic poles flip, and then return to their original orientation.
The Schwabe cycle
When the Sun is in an organized state, the center of the Sun resembles a giant vertical bar magnet with…
