// April 6th, 2012 // Comments Off on Chasing the aurora // How Things Work
A brisk wind flowed through the trees as I retreat for the car. Ignition on, -17°C outside, warm air flows through the vents. Another cold clear night – perfect for viewing the elusive aurora borealis. We’d been sitting out for almost two hours, but it was 1:20 am and we were throwing in the snap frozen towel for the night. Nada.
The next day we went on a wildlife tour, and the British travellers in front of us were showing off their pictures on a camera. “When did you see the Northern Lights,” I asked. “They look amazing!”
“Last night,” one of them replies, “about 1:30am”.
That night we stayed inside and watched TV until 1 am, then took a mug of hot chocolate and plenty of warm clothes to go aurora hunting. It’s 4:30 am before we give up, with cold noses and toeses, having missed them again. The next morning (well, afternoon by the time we wake up) we find out the lights had started early, about 10 pm.
Three more days we stay in Whitehorse, Yukon Territory, Canada, hoping for a glimpse of the lights. Once we saw a pale white streak across the sky, which showed up green on the camera under long exposure.
Disappointing, really, as we head back South – away from the elusive Northern lights.
First stop is Liard hot springs, and I recommend it a LOT. Wow, is it steamy! Anyway, we went for a dip, and as we were walking back to the accommodation, we saw them!
Green swirls, curtains and purple streaks!
The colours come from electrons around atoms jumping back and forth between orbits. Electrons absorb light to move up an orbit, then emit light of a particular wavelength to fall back down. Some excited states are more stable than others, and certain transitions happen more readily.
Green light is emitted by oxygen atoms at lower altitudes, while a red glow can be seen from another oxygen transition at high altitudes. Purple is from transitions in nitrogen molecules that emit blue and red. A mix of the colours can appear white. A great chemistry-heavy explanation of the colours can be found here.
Did you know the northern magnetic pole is moving towards Siberia at a rate of around 40 kilometres per year? Aurora hunters in the US in 2060 might be more unlucky than we were!
Here’s a screenshot of the aurora predictor on the night we snapped these pictures, to give you some idea of what the conditions were like that allowed the aurora to occur.
Want more aurora? Check out this video which describes how they occur, and shows footage from above filmed on the International Space Station.