The ability to have access to the Internet or use a mobile phone anywhere in the world is taken more and more for granted, but the brightness of Internet and telecommunications satellites that enable global communications networks could pose problems for ground-based astronomy. University of Illinois Urbana-Champaign aerospace engineer Siegfried Eggl coordinated an international study confirming recently deployed satellites are as bright as stars seen by the unaided eye.
“From our observations, we learned that AST Space Mobile’s BlueWalker 3 — a constellation prototype satellite featuring a roughly 700 square-foot phased-array antenna — reached a peak brightness of magnitude 0.4, making it one of the brightest objects in the night sky,” Eggl said. “Although this is record breaking, the satellite itself is not our only concern. The untracked Launch Vehicle Adapter had an apparent visual magnitude of 5.5, which is also brighter than the International Astronomical Union recommendation of magnitude 7.”
For comparison, the brightness of the stars we can see with an unaided eye is between minus 1 and 6 magnitude, minus 1 being the brightest. Sirius, the brightest star, is minus 1. Planets like Venus can sometimes be a bit brighter — closer to minus 4, but the faintest stars we can see are roughly magnitude 6.
“One might think if there are bright stars, a few more bright satellites won’t make a difference. But several companies plan to launch constellations,” Eggl said. “For example, Starlink already has permission to launch thousands of satellites, but they’ll probably get their full request of tens of thousands granted eventually.
“And that’s just one constellation of satellites. Europe and China want their own constellations and so does Russia. Just those in the United States being negotiated with the FCC amount to 400,000 satellites being launched in the near future. There are only 1,000 stars you can see with the unaided eye. Adding 400,000 bright satellites…