By Dr Simon Walker

The northern and southern lights – also known as the aurora borealis and aurora australis – are not only spectacularly beautiful, but they also provide valuable clues about the space environment around Earth and the growing challenges of space weather hazards.

Their story begins with the Sun. Energetic, charged particles regularly burst out from the Sun and speed towards the Earth. These particles create risks for the health of humans as they are a form of radiation. Fortunately the Earth is protected by a bubble of layers of invisible elastic bands known as a magnetic field. The energetic particles can squish and stretch the bubble but struggle to pass through it. Like water flowing around a rock, the particles are diverted around our magnetic field, stretching it as they reach Earth’s nightside. The elastic bands of our magnetic field can be stretched even beyond the moon until they cannot be stretched any further and they suddenly and explosively unstretch flinging energetic particles towards the Earth. These particles then reach an inner layer of elastic bands that represent our magnetic field and they spiral along them to the two different ends of the invisible elastic band at the north and south.

The particles then collide with our atmosphere producing the brilliant displays of the northern and southern lights. Because the energetic particles follow the same magnetic field lines into both the north and south poles, the auroras they produce are mirror images of one another.

An example of the mirrored lights can be seen in the two pictures shown below that were taken on two different planes in 1968. These planes flew at the same time towards the north and south pole at exactly geographically mirrored points. The picture on the left was taken at the north pole and picture on the right was taken at the south pole.

Image Credit: Stenbaek-Nielsen, H. C., Davis, T. N., & Glass, N. W. (1972). Relative motion of auroral conjugate points during substorms. Journal of Geophysical Research, 77(10), 1844–1858. https://doi.org/10.1029/JA077I010P01844

In a recent study: “Predictors of Substorm Onset Conjugate Displacement”, we investigated this symmetry. We used two satellites orbiting at great distances from Earth that could take pictures of northern and southern lights across the entire north and south pole. We found that these mirrored lights can be shifted east and west from each other and sometimes even north-south so that the southern lights appear closer to the south pole than the northern lights appear to the north pole and vice versa.

If the mirrored northern and southern lights are shifted in respect to each other it tells us that the bubble of elastic bands that protects us has been twisted and deformed. Our investigation showed us that the particles and radiation that is released from the Sun is responsible for the twisting and deformation of the Earth’s magnetic field. Using satellites that live 1.5 million kilometers away watching and monitoring the Sun we are now able to predict how twisted and deformed our protective bubble becomes. 

This research not only helps us better predict where the northern and southern lights will appear but is important for our understanding of space weather. The energetic particles the Sun releases pose a hazard for human space flight, electric power, satellites and even passengers on commercial flights and so much more. As we move to increasing dependence on technology, understanding what shapes and effects our protective magnetic field has never been more important.