Astronomers and other stargazers have new cause for concern about light pollution following claims that Starlink’s newest satellites, which support phone services, could appear five times brighter in the sky than existing satellites.

A recently published study (PDF) by the International Astronomical Union (IAU) claims that the Direct to Cell (DTC) satellites launched by SpaceX for its satellite business are on average 4.9 times brighter than other Starlink Mini spacecraft.

In the best-case scenario, where brightness reduction techniques are applied, the report estimates that the DTC satellites will still be about 2.6 times as bright as the others due to the lower altitude at which they operate.

The author of the research paper is the IAU Center for the Protection of Dark and Quiet Skies from Disturbance by Satellite Constellations, and the topic is so comprehensive that it is now referred to simply as CPS.

As The registry As reported last year, increasing light pollution from various sources, including reflections from satellites in low Earth orbit (LEO), is already affecting the view of the night sky, particularly affecting astronomers trying to glimpse distant objects in the universe.

Starlink confirmed a successful test of its technology in January 2024 using the first DTC satellites it launched into orbit. Elon Musk’s company plans to partner with T-Mobile US to offer a service that will allow subscribers to make calls via satellite using unmodified cell phones in areas without coverage from terrestrial cell towers.

As SpaceX noted in a webcast at the time, “We expect these first six Starlink direct-to-cell satellites to be slightly brighter than the previous Starlink V2 Minis.”

According to the IAU report, following the successful tests, Starlink has applied to the U.S. Federal Communications Commission (FCC) for a license modification that would allow the operation of 7,500 of the new units in an orbit between 340 and 345 km.

These satellites will complement the 7,500 existing Starlink units, which operate at higher altitudes and are slightly larger (125 m² compared to 116 m²) due to the antenna required for DTC communication.

However, the study notes that the early Starlink DTC satellites appear to be on average 4.9 times brighter than existing satellites, but it is not known what dimming techniques were in use at the time of the observations.

In other words, it’s possible that Starlink didn’t use mitigation measures at the time. If they were applied in the future, they could limit light pollution from the hardware in orbit.

We have asked Starlink for a comment.

The study also found that these satellites spend more of their time in the Earth’s shadow than those operating at higher altitudes, partially mitigating their impact on astronomical observations.

Meanwhile, rival satellite operator AST SpaceMobile received a provisional license for space-based operations from the FCC this week, authorizing the launch of the first five BlueBird satellites, which will also support phone and broadband services. Launch is scheduled for sometime in September.

“This regulatory milestone is a significant step toward nationwide coverage of the continental United States from space in premium cellular spectrum,” said Scott Wisniewski, president of AST SpaceMobile, in a statement.

The BlueBird satellites are described by the company as “the largest commercial communications systems ever deployed in low Earth orbit.” Their antenna alone is said to be 64 m long.² so large that they can focus a radio beam with a smaller area of ​​the earth’s surface to limit interference with other services.

Last year, AST SpaceMobile’s BlueWalker 3 satellite, a test vehicle for its satellite broadband service, was reported to be at times the brightest object visible in the night sky.

We asked AST SpaceMobile what measures it has taken to minimize light pollution from its satellites and will keep you updated with any answers. ®