Today’s APOD feature has just left me speechless. What is this astronomical beauty, this celestial rose, this heavenly gate I am staring at in this photo, taken after sunset on September 1, above the cold Chilean highlands?
Those reddish petals are not clouds, but luminous glowing air, caused by chemiluminescence, as experts over at APOD explains:
Above a sea of clouds and flanking the celestial Milky Way, the airglow seems to ripple and flow across the northern horizon in atmospheric waves. Originating at an altitude similar to aurorae, the luminous airglow is instead due to chemiluminescence, the production of light through chemical excitation. Commonly captured with a greenish tinge by sensitive digital cameras, this reddish airglow emission is from OH molecules and oxygen atoms at extremely low densities and has often been present in southern hemisphere nights during the last few years. On this night it was visible to the eye, but seen without color.