Take a look at the stunning image of ‘airglow’ outlining Earth's horizon. NASA shares pic

livemint.com:

A post shared by NASA (@nasa) Apart from the radiating Earth's horizon, the citylights of Denver and Chicago lit up a beautiful pattern of lights at the Earth's surface. “Lights from cities dot Earth’s surface – among them, a concentration of lights near the horizon identify the city of Chicago, while the concentration of lights closer to the bottom left identify Denve," it added.

NASA describes ‘airglow’ as a phenomenon that occurs when atoms and molecules in the upper atmosphere emit light to shed their excess energy. It can happen when atoms and molecules that have been ionized by sunlight collide with and capture a free electron.

Due to constant collision, these atoms eject a particle of light, called a photon, making the phenomenon look similar to that of auroras. However, auroras are the result of high-energy particles originating from the solar wind, airglow is energized by ordinary, day-to-day solar radiation.

“Similar to auroras, except auroras are driven by high-energy particles originating from the solar wind – airglow is sparked by day-to-day solar radiation," said NASA in its Instagram post. Study of the Earth's airglow provides details of the upper atmosphere’s temperature, density, and composition.