One of the brightest objects in the night sky is a human-made satellite

A prototype satellite has become one of the brightest objects in the night sky, and it may soon be accompanied by dozens more. An observation campaign tracking the BlueWalker 3 satellite, launched in September 2022 by AST SpaceMobile, found that it is at times brighter than all but a handful of stars and planets that can be seen from Earth. The findings published in the journal Nature highlight a fast-escalating concern among astronomers, who have warned that the influx of private space ventures in low-Earth orbit could alter our view of the night sky and interfere with research.

Researchers with the International Astronomical Union’s Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS) observed BlueWalker 3 over the course of 130 days. BlueWalker 3’s antenna array measures just shy of 700 square feet, making it the largest yet for a commercial satellite in low-Earth orbit. That huge array reflects sunlight and after it unfurled, its brightness spiked. The effect isn’t constant, but instead fluctuates depending on factors like the satellite’s position relative to the sun, and the viewing angle. The CPS team observed it from sites in Chile, the US, Mexico, New Zealand, the Netherlands, and Morocco.

“These results demonstrate a continuing trend towards larger, brighter commercial satellites, which is of particular concern given the plans to launch many more in the coming years,” said Siegfried Eggl, one of the co-authors of the study. “While these satellites can play a role in improving communications, it is imperative that their disruptions of scientific observations are minimized.” AST SpaceMobile eventually plans to deploy a fleet of roughly 100 cellular broadband satellites based on the BlueWalker 3 design.

SpaceX, whose thousands of Starlink satellites have repeatedly come under scrutiny for their potential impact on the night sky, has experimented with dark coatings to cut down on the amount of reflected light, to limited success. For astronomers, to whom it poses a growing headache, it's not enough. Stations observing from the ground will need to develop satellite avoidance strategies to work around these artificial constellations, the researchers note in the paper.

And, visibility isn’t the only problem. Commercial satellites, including BlueWalker 3, flooding low-Earth orbit also threaten to interfere with radio astronomy. A separate study led by the CPS and published earlier this year found Starlink satellites are leaking “unintended electromagnetic radiation” that could disrupt radio telescope observations. 

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