The night sky has been the canvas of humanity\u2019s wonder for millennia. The stars guided sailors, inspired poets, and offered astronomers the first glimpse into an infinite universe. But today, the ancient map is being redrawn, not by nature but by technology.<\/p>\n
The number of satellites in orbit around Earth has exploded from fewer than 8,000 satellites before 2019 to over 14,000 now. Many are from SpaceX\u2019s own Starlink network, which aims to provide worldwide Internet coverage. But this is just the start. A total of over 1.7 million satellites (many of which are exceptionally bright) are from proposals currently awaiting approval, with Hubble being the most optimistic one.<\/p>\n
According to a new study from the European Southern Observatory (ESO), the consequences would be catastrophic.<\/p>\n
\u201cUntil now we have managed, but it\u2019s getting worse,\u201d stresses Olivier Hainaut, an ESO astronomer who has studied the issue for decades.<\/p>\n
Study Evaluates Impact of Satellite Constellations on Astronomical Observations<\/a><\/p>\n His peer-reviewed analysis, accepted for publication in Astronomy & Astrophysics, concludes that astronomy could only survive if the total number of satellites is limited to 100,000 faint ones, below naked-eye visibility. Anything more, he warns, would have \u201cdevastating consequences for astronomy.<\/p>\n SpaceX alone plans to send one million satellites into orbit, including space-based data centers. Hainaut\u2019s simulations show that on clear nights, hundreds of satellites would be visible at once, and at certain times, thousands, matching the number of stars seen with the naked eye under pristine conditions.<\/p>\n Other companies are joining the race. E-Space\u2019s Cinnamon constellation and China\u2019s CTC-1 and 2 projects could add hundreds of thousands more satellites. And then there is Reflect Orbital, a U.S. start-up with perhaps the most audacious plan: launching mirror-like satellites to reflect sunlight at night. Their beams would cover five kilometers on Earth\u2019s surface.<\/p>\n Hainaut\u2019s calculations are stark. A single Reflect Orbital satellite, seen from within its beam, would appear four times brighter than the full Moon. Outside the beam, each satellite would still shine as brightly in the night sky as Venus does as a \u201cmorning star.\u201d In light-polluted cities like Munich, these satellites may be the only \u201cstars\u201d we see in the sky.<\/p>\n Astronomers already struggle with satellite streaks across their images.<\/p>\n \u201cSatellites, illuminated by the Sun, are much brighter than distant galaxies. When a satellite crosses what we observe, it makes a bright streak on our image, zapping whatever is behind it,\u201d explains Hainaut.<\/p>\n His simulations show that with SpaceX\u2019s mega-constellation, dozens of trails would appear in each image taken just two hours into the night with ESO\u2019s Very Large Telescope in Chile.<\/p>\n That represents field-of-view losses of up to 28%. For sensitive instruments like the Vera C. Rubin Observatory\u2019s wide-field camera, the damage could be worse: entire nights of data rendered unusable.<\/p>\n Reflect Orbital\u2019s satellites would be even more destructive. Even if none pointed directly at an observatory, their trails could spoil every image when illuminated by the Sun.<\/p>\n But the problem isn\u2019t only streaks. Faint satellites add a diffuse glow, while brighter ones scatter light through the atmosphere. Together, they raise the background brightness of the night sky.<\/p>\n Hainaut\u2019s study is the first to quantify this effect, showing that very bright constellations could make the sky three to four times brighter overall.<\/p>\n The impacts extend beyond telescopes. \u201cSending thousands of satellites has implications: economic, ecological, and astronomical,\u201d says Hainaut. He notes that light pollution from bright constellations can disrupt ecosystems and biological clocks. Launching and maintaining thousands of satellites also affects air quality, while their fiery re-entry pollutes the atmosphere.<\/p>\n \u201cMy job is astronomy, so I quantify the effects on astronomy,\u201d he adds. \u201cI hope others will evaluate the other impacts in their field of expertise.\u201d<\/p>\n Hainaut concludes that only by capping satellites at 100,000 faint ones can astronomy survive. \u201cThis is not a hard number, like 99,999 is good and 100,001 is bad: clearly I\u2019d prefer 50,000,\u201d he says. \u201cBut 100,000 causes losses at about the level of other technical losses, such as equipment failure.\u201d Crucially, he adds, satellites must be fainter than visual magnitude 7, invisible to the naked eye.<\/p>\n The study has already influenced policy. ESO, together with the UK\u2019s Royal Astronomical Society and the International Astronomical Union, submitted it to the U.S. Federal Communications Commission (FCC) in response to filings by SpaceX and Reflect Orbital.<\/p>\n