September 1, 2014
The light from the farthest visible stars set out on its journey long before your first birthday.
Airglow Ripples over Tibet
Birthday · September 1, 2014
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 September 1, 2014. 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 above. 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. Now Available: APOD 2015 Wall Calendars
Image credit: Jeff Dai