 |
 |
|
|
|
|
|
About - Submit | Optics Picture of the Day | Galleries | Previous | Next | Today |
Most airglows occur at well defined heights where the balances between UV excitation, collisional de-excitation and re-radiation are just right.
This ISS image over night-side Earth shows the green (oxygen) and yellow (sodium) layers.
M42 and Orion's belt stars are at centre.
The sun’s extreme ultraviolet shines on Earth’s thermosphere. It is (thankfully for us) absorbed and produces excited oxygen atoms and nitrogen molecules. These collide and excite other atmosphere components that slowly lose their energy by radiating into the night – airglow.
Green airglow from oxygen atoms is the most common. Reds from oxygen and OH radicals are also seen as are yellow sodium and even blue oxygen airglows.
Alvin Wu’s airglow is remarkable for its strong structure. There is a near continuous zone of green oxygen glow bordered by yellow and red bands.
The bands are imprints of gravity waves travelling upwards from the lower atmosphere. The waves modulate the upper atmosphere temperatures and collisional de-excitation processes. The latter compete with the radiative de-excitation that makes airglow. The gravity waves write themselves in the airglow.
