"Colors of the Night - Iceland" (a winter night). Photo © Louis Leroux. AstroBin image of the day 6 June '25. Part of the image includes Airglow. Photographer's description: "The second striking phenomenon, covering the entire sky, is airglow. These colorful bands stretching across the sky result from complex chemical reactions occurring in the upper atmosphere, specifically in the thermosphere, which is a layer within the ionosphere. Caused by solar radiation, powerful ultraviolet rays dissociate certain molecules in Earth's atmosphere. These excited molecules then emit a faint glow in the dark night, a phenomenon known as chemiluminescence. The red color comes from hydroxyl molecules. Sodium and oxygen atoms rise to about 100 km in altitude and produce green or even orange light. Blue airglow is much rarer and occurs even higher up. A recent study has confirmed a link between this phenomenon and gravity waves."