By Dr Martin George
October was a wonderful month for displays of the aurora australis, also known as the southern lights. Here at the Ulverstone Planetarium we are often asked about them – what causes them, and when to see them.
Auroral displays (which are known as the aurora borealis in the northern hemisphere) are triggered by tiny charged particles from the Sun – protons and electrons – as they reach Earth and interact with Earth’s magnetic field, which surrounds our planet and is the same field that makes a compass needle point in a particular direction. The interaction causes geomagnetic storms, during which particles impinge on our upper atmosphere, causing it to glow with light of different colours, most commonly green and red. Many of these particles are those that were already trapped in the field, but some of the solar particles are also involved in these collisions with the atmosphere.
We see more auroral displays when the Sun is most active. This happens about every 11 years, and right now (2024) we are about to reach such a peak. Especially relevant are coronal mass ejections from the Sun, which are enormous bursts of particles. This is what caused the wonderful displays of 11 October, both in the early morning and during the evening.
Prediction of auroral displays is not an exact science! However, we do monitor the Sun for activity, and often get about two days’ notice of a possible display. Even when the Sun has unleashed an especially large number of particles, the orientation of another magnetic field – the interplanetary magnetic field – needs to be pointing in a particular direction in the vicinity of Earth for a good display to result. On 11 October the conditions were perfect!
To get your best chance of seeing an aurora, watch the sky whenever you can! Being away from the lights of towns and cities is important, as is allowing your eyes several minutes to adjust to the darkness. There are many websites that offer predictions for certain dates to look. While containing a lot of scientific information, one of the best is spaceweather.com. General comments near the top of the page will give you a good idea of what is happening.