Coming home from dinner with friends a few weeks ago, I noticed the sky was clear, writes Ian Griffin.
The moon was high in the west, its bright light painting the harbour. As usual, I checked an app on my phone to see if the southern aurora could be seen. To my surprise (because space weather was expected to be mild), it looked like there might be some display shuffling.
I grabbed my camera and a tripod and headed to a favorite spot near Hoopers Inlet. With no aurora apparent to the naked eye, I set up my camera and started taking pictures. Much to my excitement, despite the lack of visual activity, a beautiful pastel glow was apparent as each image appeared on camera. Although not the most active aurora I’ve seen, the chartreuse and salmon auroral hues created a beautiful backdrop for the hills that kiss the inky water of the creek.
Modern cameras are significantly more capable than human eyes of detecting faint hues. While I could (just) discern a clearing of the sky, to me this display was otherwise colorless.
This particular display of the aurora australis was fading when I arrived and finally disappeared entirely just before midnight. I packed up my camera and went home to see the results on my computer. My favorite photo accompanies this column; on a night when my eye saw no color, the camera captured an astonishing range of nighttime hues on land, sea and sky.
Each color comes from a different mechanism. The sky appears blue because the Earth’s atmosphere preferentially scatters blue light more than any other color. The green and red auroral colors are created by particles from the solar wind colliding with molecules above the Earth’s surface in a region called the thermosphere. Finally, if you look closely, near the top of the image, there is another patch of dark red light. It’s glowing hydrogen gas in the Eta Carina Nebula, which lies more than 7,000 light-years beyond the hills of the Otago Peninsula.