Amazing Aurora

What causes the Aurora Borealis?

Let's travel down to 2400 kilometers under the Earth's surface. That's where you would be if you went straight down in an airplane for an entire 2.5 hours. Down here, molten iron shifts around due to convection currents. At this heat, the heavily ionized material is in fluid-like motion (yellow ribbons in Figure 1). When something is ionized, it's usually been removed of one or more of its electrons, giving the material an electrical charge. The movement of these electrical charges creates an electric field. Paired with special relativity, the presence of an electric field will also create a magnetic field (a future article will discuss this in-depth).

Figure 1

Figure 2

The black arrows in Figure 1 represent the lines of the magnetic field. These are the same blue lines in Figure 2. The movement of molten iron deep inside the Earth creates a strong magnetic field that has effects that extend far beyond the Earth's atmosphere.

Now let's travel in the opposite direction. We'll go 150 million kilometers away, towards the sun. This flight would take about 20 whole years (that 2.5 hour-long flight to the Earth's core seems pretty short now, doesn't it). The processes inside the Sun are very similar to those of the Earth, only with a couple of differences. For example, while the Earth has molten metals moving around the core, the Sun has a large amount of plasma. Plasma is a gaseous molecule that has been stripped of one or more of its electrons. This tends to occur at extremely high temperatures. Since most plasma is missing an electron, it is electrically charged, like the molten iron in the Earth's core. Once again, the movement of electrically charged materials creates a magnetic field. The sun's magnetic field is constantly fluctuating due to random variations in the plasma currents. Sometimes, the plasma gets concentrated and extremely heated in small areas. Here, the increased temperature will cause the plasma to expand with a force stronger than the gravity of the Earth can hold down. This plasma is pushed up and the magnetic field of the sun guides it away from the Sun's core. These solar winds are projected outwards into space (Figure 3).

Figure 3

Figure 4

Many of these solar winds approach the Earth, posing a threat to our atmosphere. However, the Earth's magnetic field serves as a shield, pushing off the electrically charged material away from the Earth (Figure 4). However, near the poles, the Earth's magnetic field caves in. At these points, solar winds can enter the atmosphere and interact with atmospheric hydrogen and nitrogen. The collisions between the oxygen/nitrogen atoms and the solar wind energetically excite atoms. In an effort to return to their ground state, these atoms release photons, or light. The photons are released at different frequencies, creating the different colored lights that we perceive as the stunning Aurora Borealis (Figure 5).

Figure 5