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.
These are the depictions of the most intense meteor storm in recorded history – the Leonid meteor storm of 1833. The Leonid meteor shower is annually active in the month of November, and it occurs when the Earth passes through the debris left by the comet Tempel-Tuttle. While the typical rates are about 10 to 15 meteors per hour, the storm of 1833 is speculated to have been over 100,000 meteors per hour, frightening people half to death. Here’s how Agnes Clerke, an astronomer witnessing the event, described it: “On the night of November 12-13, 1833, a tempest of falling stars broke over the Earth… The sky was scored in every direction with shining tracks and illuminated with majestic fireballs. At Boston, the frequency of meteors was estimated to be about half that of flakes of snow in an average snowstorm.” (x)