Rainbow waves illuminate Azores sky with stunning celestial display

This is a photo taken of Mount Pico in the Azores archipelago of Portugal. In the center of the photo, a bright band of our galaxy stretches horizontally, and in the upper left, the Andromeda Galaxy (M31) can be seen. The reason the sky shines like a rainbow is due to airglow. Airglow is a phenomenon where atmospheric components that have absorbed sunlight during the day emit a faint glow at night. Usually, it is too faint to be noticeable, but when atmospheric disturbances occur, gravity waves in the Earth's atmosphere are generated, creating wave patterns in the sky, similar to when a stone is thrown into calm water. The deep red hue is the light emitted by OH molecules (small molecules formed by a combination of oxygen (O) and hydrogen (H)) at an altitude of about 87 km that have been exposed to ultraviolet radiation, while at higher altitudes, sodium atoms produce an orange light, and oxygen atoms create a green light.