Milky Way over Visible & Infrared Survey Telescope for Astronomy (VISTA) in Chile
In this view of the Paranal Observatory, the Milky Way galaxy forms an arc across the Atacama night sky, along with colorful atmospheric airglow. Below it stands VISTA, the Visible and Infrared Survey Telescope for Astronomy.
Airglow occurs when atoms and molecules in the upper atmosphere, excited by sunlight, emit light to shed their excess energy. Or, it can happen when atoms and molecules that have been ionized by sunlight collide with and capture a free electron. In both cases, they eject a particle of light—called a photon—in order to relax again. The phenomenon is similar to auroras, but where auroras are driven by high-energy particles originating from the solar wind, airglow is energized by ordinary, day-to-day solar radiation.
Unlike auroras, which are episodic and fleeting, airglow constantly shines throughout Earth’s atmosphere, and the result is a tenuous bubble of light that closely encases our entire planet. (Auroras, on the other hand, are usually constrained to Earth’s poles.) Just a tenth as bright as all the stars in the night sky, airglow is far more subdued than auroras, too dim to observe easily except in orbit or on the ground with clear, dark skies and a sensitive camera. However, it is a marker nevertheless of the dynamic region where Earth meets space . . .
https://www.eso.org/public/teles-instr/paranal-observatory/surveytelescopes/vista/
Image Date: Oct. 15, 2014
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