The Brightness of the Night Sky

The night sky brightness, together with number of clear nights, seeing, transparency, photometric stability and humidity, are some of the most important parameters that qualify a site for front-line ground--based astronomy. While there is almost no way to control the other characteristics of an astronomical site, the sky brightness can be kept at its natural level by preventing light pollution in the observatory areas. This can be achieved by means of extensive monitoring programmes aimed at detecting any possible effects of human activity on the measured sky brightness.

Night sky at ESO-Paranal (Chile). Photo by L. Vanzi (ESO).

Comparison between a night sky spectrum taken at Cerro Paranal-Chile during dark time (lower panel) and one taken in Asiago-Italy (upper panel). Light pollution is clearly visible in the form of Sodium and Mercury emission lines in the blue/visible part of the spectrum.

Night Sky Data Downloads

Movies and other media

Publications and Reports

• UBVRI night sky brightness at ESO-Paranal during sunspot maximum (A&A 2003, PDF)
• A robust algorithm for sky background computation in CCD images (A&A 2003, PDF)
• OBserving in bright time: tips & tricks (ESO Messenger n. 118)
• UBVRI night sky brightness at ESO-Paranal during sunspot maximum (ESO Messenger n. 115)
• UBVRI twilight sky brightness at ESO-Paranal (A&A 2006, PDF)
• Where the shadows lie - The dark skies of Chile (Zenith)
• Impact of optical and near-IR sky brightness on Site Evaluation (ESO internal report)
• The Dancing Sky: six years of night sky observations at Cerro Paranal (Starlight 2007 conference proceedings, PDF)
• The Dancing Sky: six years of night sky observations at Cerro Paranal (A&A 2008, PDF)
• The effects of improper lighting on professional astronomical observations (CIE 2010, PDF)

PPT Presentation

A few related links

• International Dark-Sky Association
• On light pollution (ISTIL)
• Night sky brightness at Cerro Pachon
• La Palma night-sky brightness
• Night sky brightness at Mauna Kea