Light pollution at the world’s major astronomical observatories

This graph shows the impact of light pollution on all 28 major astronomical observatories, with ESO’s Paranal Observatory featuring as the darkest site among them. It is taken from a study by Falchi and collaborators, published in 2023 in Monthly Notices of the Royal Astronomical Society. It uses a logarithmic scale and compares the brightness directly above the observatories to the natural background brightness (1% means there is 1% more light pollution, 100% means there’s 100% more light pollution, so twice as much as without artificial sources of light). Note that some observatories appear twice: for example, Armazones, where ESO’s Extremely Large Telescope is located, has more light pollution during the construction of the telescope, when a temporary workers’ lodge is in place.

This plot is a slightly adapted version of Figure 1 from the Falchi et. al study. Here, the site locations are shown in the vertical axis, with added flags, and the labels on the horizontal axis have been modified for improved readability.