The ESOcast 78 is here. ESO has a series of video podcasts in which they explain a ton of things from what a telescope if, to how a black hole works. In this newest ESOcast we learn about the airglow, the coloured light which can be seen at night.
In the last decades the airglow can be seen even more and more in the Paranal desert of Chile where ESO has a number of astronomical observatories like NTT, VLT and the AMLA microwave telescope.
Airglow has color red at about 100 km altitude and is greenish from 150-300 altitude. The color is given off by the oxygen and nitrogen molecules from the air after they have been in contact with UV light from the Sun during the day. Because of the UV light the oxygen and nitrogen molecules are broken apart and at night they try to form new bonds and thus release the red and green light from their atoms.
A nice thing to see, although it hinders astronomers from seeing distant stars.