It was the best of times, and it was undoubtedly the epoch of incredulity last Friday night when I found myself perched beside one of the Otago Peninsula's back bays, for the second time in a week, observing an epic overhead display of the aurora australis. My happiness was almost unbounded as I clapped, shouted, and snapped away with an array of cameras. Despite the bright moonlight, on both nights the sky appeared blood red, with dazzling dancing luminous flashes appearing, seemingly randomly. Experiencing a single all-sky aurora is a thrill, but to witness two within the span of three days is a rare and privileged event. So, what was going on, I hear you ask?
All the world's a stage, and on the celestial stage, the sun plays a critical role in creating auroras. When the solar windstreams of charged particles ejected from the sun travel through space, they interact with the Earth's magnetic field. These charged particles collide with atoms and molecules in the Earth's atmosphere as they are drawn toward the poles. This interaction excites the atmospheric gases, causing them to emit light in a dazzling display of colours, from vibrant greens to deep reds and purples.
If you really want to hear about it, the first thing you'll probably want to know is why we are seeing so many bright auroras this year. The reason is that we are approaching the peak of the 11-year sunspot cycle. This cycle is driven by the sun's magnetic field, which undergoes a transformation as it twists and turns due to differential rotation and convection processes within the solar interior. As the magnetic field lines become tangled, sunspots — dark regions on the sun's surface — form where magnetic activity suppresses the heat flow. These sunspots increase in number until they peak during solar maximum, leading to heightened solar activity, including flares and coronal mass ejections, giant explosions which gave rise to the two displays local stargazers enjoyed last week. Let us go then, you and I, to enjoy this plethora of auroras!
