Nocturne captures an aurora’s pastel glow
Arriving home after dinner with friends a few weeks ago, I noticed the sky was clear. The moon was high in the west, its bright light painting the harbour. As is my habit, I checked an app on my phone to see whether the southern lights might be visible. To my surprise (as space weather conditions were expected to be benign) it looked like there might be a display brewing.
I grabbed my camera and a tripod and headed to a favourite spot beside Hoopers Inlet. With no aurora apparent to the naked eye, I set up my camera and began to snap away. To my excitement, despite the lack of visual activity, a beautiful pastel glow was apparent as each picture appeared on the camera. While this was not the most active aurora I have seen, the chartreuse and salmon auroral tints created a beautiful backdrop to the hills that embrace the inlet’s inky water.
Modern cameras are significantly more capable than human eyes at detecting faint hues. While I could (just) discern a lightening of the sky, for me, this display was otherwise colourless.
This particular display of the aurora australis was fading as I arrived and eventually disappeared entirely just before midnight. I packed up my camera and headed home to view the results on my computer. My favourite picture accompanies this column; on a night when my eye saw no colour, the camera captured a stunning array of nocturnal shades on land, sea and sky.
Each colour comes from a different mechanism. The sky appears blue because Earth’s atmosphere preferentially scatters blue light more than any other colour. The green and red auroral colours are created by particles from the solar wind colliding with molecules high above Earth’s surface in a region called the thermosphere. Finally, if you look carefully, near the top of the picture, there is another deep red patch of light. This is glowing hydrogen gas in the
Eta Carina nebula, which is more than 7000 light years beyond the hills of Otago Peninsula.