|Airglow is a faint luminescence of the earth’s upper atmosphere. The emitted electromagnetic
radiation results mainly from photo-chemical reactions of upper atmospheric constituents.
Although ionic recombination and bombardment by energetic particles are other mechanisms
that can cause airglow, the main emissions include the atomic oxygen forbidden green
line (5577A) and forbidden red line (6300A), the sodium doublet (5890A and 5896A),
and the hydroxyl (OH) band system. This airglow is produced in a 10 to 20 km thick
zone at an altitude of about 100 km. This airglow can be seen by the naked eye on
a dark night away from city lights.