APOD: 2023 January 11 – Spiral Aurora over Iceland

Good morning, Rallypoint, and welcome to the January 11th edition of Astronomy Picture of the Day (APOD): "Spiral Aurora over Iceland." Gatklettur (aka the Hellnar Arch) is a naturally formed stone arch found between the villages of Arnarstapi and Hellnar on the northwest coast of Iceland. This spiral aurora was photographed over Gatklettur in November 2022. Multiple foreground and background exposures were captured from a single camera at a set location. The 'mist' over the rocks surrounding the stone arch was created by moving waves during each long exposure.

As you may know already, gases exist in their atomic (versus molecular) form at high levels in our atmosphere, and these gases interact with radiation from the Sun to produce an aurora. When atoms shed excess energy, they do so in the form of light at wavelengths that are particular to the atom itself. The colors in this aurora suggests that oxygen (green) is the primary agent. The purple 'fringe' to the auroral curtain is due to the presence of nitrogen.