Free Astronomy Magazine May-June 2020

46 MAY-JUNE 2020 is more pronounced for long expo- sures (of about 1000 s), up to 3% of which could be ruined during twi- light, the time between dawn and sunrise and between sunset and dusk. Shorter exposures would be less impacted, with fewer than 0.5% of observations of this type af- fected. Observations conducted at other times during the night would also be less affected, as the satellites would be in the shadow of the Earth and therefore not illuminated. De- pending on the science case, the im- pacts could be lessened by making changes to the operating schedules of ESO telescopes, though these changes come at a cost. On the in- dustry side, an effective step to mit- igate impacts would be to darken the satellites. The study also finds that the greatest impact could be on wide-field sur- veys, in particular those done with large telescopes. For example, up to 30% to 50% of exposures with the The impact of satellite constellations on astronomical observations A stronomers have recently raised concerns about the impact of satellite mega-con- stellations on scientific research. To better understand the effect these constellations could have on astro- nomical observations, ESO commis- sioned a scientific study of their impact, focusing on observations with ESO telescopes in the visible and infrared but also considering other observatories. The study, which considers a total of 18 repre- sentative satellite constellations under development by SpaceX, Amazon, OneWeb and others, to- gether amounting to over 26 thou- sand satellites, has now been accepted for publication in Astron- omy & Astrophysics . The study finds that large telescopes like ESO’s Very Large Telescope (VLT) and ESO’s upcoming Extremely Large Telescope (ELT) will be “mod- erately affected” by the constella- tions under development. The effect by ESO US National Science Foundation’s Vera C. Rubin Observatory (not an ESO facility) would be “severely af- fected”, depending on the time of year, the time of night, and the sim- plifying assumptions of the study. Mitigation techniques that could be applied on ESO telescopes would not work for this observatory al- though other strategies are being actively explored. Further studies are required to fully understand the sci- entific implications of this loss of ob- servational data and complexities in their analysis. Wide-field survey tel- escopes like the Rubin Observatory can scan large parts of the sky quickly, making them crucial to spot short-lived phenomena like super- novae or potentially dangerous as- teroids. Because of their unique capability to generate very large data sets and to find observation tar- gets for many other observatories, astronomy communities and fund- ing agencies in Europe and else-