Keeping the sky dark and quiet: Recommendations for non-interference with astronomy

Our window to the night sky is getting more and more opaque, as we are progressively widening the reach of artificial lighting on Earth. Besides interfering with nature and with human's view of the stars, artificial light impacts astronomical observations. With the recent large increase in numbers of telecommunication satellites launched in low Earth orbit, some are visible even with the naked eye and the appearance of the pristine night sky, particularly when observed from dark sites, is altered. Observations from ground-based astronomical observatories are similarly impacted whenever these objects cross the instrument's field of view. The perspective of hundreds of satellites saturating astronomical instruments leads to question whether legal instruments should be considered to regulate the maximum brightness of a satellite. Since the Outer Space Treaty, governments have agreed, through the United Nations, treaties and guidelines that, collectively, have been governing activities in outer space for over half a century. In February 2020, the International Astronomical Union expressed concern about the negative impact that the planned constellations of communication satellites may have on astronomical observations and on the pristine appearance of the night sky. To address the impact of all types of illuminations and orbiting objects on astronomy, the United Nations Office for Outer Space Affairs and Spain, with the International Astronomical Union, are holding a conference dedicated to dark and quiet skies for space and society in April 2021. In advance of the conference, a workshop took place online, from 5 to 9 October 2020, with support from the Instituto de Astrofisica de Canarias and from the USA National Optical-Infrared Astronomy Research Laboratory. The workshop resulted in preliminary reports on the extent of the issue and draft recommendations, to foster discussions between astronomers, public authorities and lighting equipment manufacturers, as well as the companies launching and operating satellite constellations. The Paper presents outcomes of the workshop and the next steps of the initiative.