November 20, 2022
A birthday is what happens when cosmic time briefly puts down the scale of eons and pays attention to a single human year.
Airglow Ripples over Tibet
Birthday · November 20, 2022
A little universe, just for you
Your date.
Ready to give.
Free PNG · 1080 × 1350 · No account needed
Image rights and credit requirements apply when sharing or reusing imagery.
Date & occasion only
Change the year
APOD published November 20, 2022. Credit: Jeff Dai. A publication-date match, not a photo taken on your date. Independent of NASA.
Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured here. The unusual pattern is created by atmospheric gravity waves, waves 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.
Image credit: Jeff Dai