An Airglow Fan from Lake to Sky
Why would the sky look like a giant fan? Airglow . The featured intermittent green glow appeared to rise from a lake through the arch of our Milky Way Galaxy , as captured last summer next to Bryce Canyon in Utah , USA. The unusual pattern was created by atmospheric gravity waves , ripples of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up . Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence , the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark. Follow APOD on: Facebook , Google Plus , or Twitter