Free Astronomy Magazine September-October 2026

11 SEPTEMBER-OCTOBER 2026 ASTRO PUBLISHING ground sky brightness. With the full 50,000 Reflect Orbital satellites, the sky would be up to three to four times brighter overall. Hainaut concludes that the proposed 1.7 mil- lion new satellites would have drastic consequences for ground-based as- tronomy. These im- pacts can only be avoided by limiting the total, of both ex- isting and future satel- lites, to 100,000 satel- lites faint enough not to be seen with the naked eye from a dark site. “This is not a hard number, like 99 ,999 is good and 100,001 is bad: clearly I’d prefer 50,000,” says Hainaut. “But 100,000 causes losses at about the level of other technical losses, such as equipment failure.” However, he adds, the sat- ellites must be fainter than visual magnitude 7; should some of them be too bright — above the minimum threshold for naked-eye visibility — the total number would need to be much lower. SpaceX and Reflect Orbital, respon- sible for the most extreme new pro- posals, have each filed with the US Federal Communications Commis- sion (FCC) for permission to launch. This new study served as the basis for a response to the FCC on these proposals by ESO, in collaboration with the UK’s Royal Astronomical Society and the International Astro- nomical Union. “The FCC received over 1800 com- ments regarding Reflect Orbital and nearly 1500 comments on the ap- plication by SpaceX,” explains ESO Institutional Affairs Officer Betty Kioko, responsible for coordinating ESO’s response to the proposals. “The ball is now in the FCC’s court, “Astronomy generates huge val- ue for humankind, including scientific, technical, econom- ical, and educational, and helps us understand our place in the Universe,” says ESO Director Gen- eral Xavier Barcons. “The large number of planned satellites in low-Earth orbit chal- lenges that capaci- ty, underscoring the need to limit future satellite launches and for astronomers, engi- neers, satellite opera- tors and other stake- holders to work together to adopt strict mitigation measures.” “Sending thousands of satel- lites has implications: economical, ecological, and astronomical,” adds Hainaut. Light pollution from very bright satellite constellations can im- pact the health and functioning of life on Earth, by disrupting biologi- cal clocks and ecosystems. Large con- stellations also have direct impacts on air quality from the numerous launches required to send and main- tain thousands of satellites, as well as from the atmospheric pollution caused as they burn up on re-entry at the end of life. “ My job is astron- omy, so I quantify the effects on as- tronomy,” explains Hainaut, “I hope others will evaluate the other im- pacts in their field of expertise.” Hainaut concludes: “Low Earth orbit is a celestial seashore that provides immense value to modern life, from global connectivity to our clear ac- cess to the Universe. However, we must manage the footprint of mega- constellations — from the light pol- lution affecting astronomy to the atmospheric effects of satellite re- entry — to ensure this resource re- mains pristine and accessible for future generations.” T his diagram shows the number of satellites that would be visi- ble above ESO’s Very Large Tele- scope (VLT) if SpaceX launches their planned constellation of 1 million satellites. The calculations were done about two hours after sunset, well into the truly dark part of the night. The grey dots are satellites in the Earth’s shadow and therefore in- visible, whereas the coloured dots are illuminated satellites. The or- ange dots, almost 2000 of them, cor- respond to satellites brighter than magnitude 7 –– the faintest bright- ness visible to the naked eye from extremely dark locations. The red dots, more than 200, are satellites brighter than magnitude 5, which corresponds to the faintest objects visible to the naked eye from a sub- urban location. [ESO/O. Hainaut] and we wait to see the determina- tions they make on both filings. For optical astronomy, this is an existen- tial threat, and we hope that the regulators will share that view.” !