Study Finds 1.7 Million Satellites Raise Night Sky Brightness

A peer-reviewed study accepted for publication in Astronomy & Astrophysics calculates that planned satellite constellations could raise the brightness of the night sky and interfere with telescope observations. The research, led by an astronomer at the European Southern Observatory, models the effect of more than 1.7 million satellites on instruments including the Very Large Telescope in Chile.

It projects field-of-view losses of up to 28 percent from satellite trails in some exposures.

There are currently 17,501 satellites in orbit, of which about 10,000 are active Starlink units, according to Orbital Radar data cited in the study. SpaceX has approval or applications for 20,000 Starlink satellites and has filed plans for an additional one million satellites intended for orbital data centers.

Other proposed systems include Reflect Orbital’s planned 50,000 mirror satellites, E-Space’s Cinnamon constellation, and China’s CTC-1 and CTC-2 projects.

The study finds that satellites illuminated near twilight produce the strongest interference. Wide-field instruments such as the camera at the Vera C. Rubin Observatory could experience detector saturation and unusable images from single trails. Reflect Orbital’s satellites are modeled to appear up to four times brighter than the full moon when viewed inside a reflected beam and as bright as Venus when viewed from outside the beam.

Orbital have each submitted filings to the U.S. Federal Communications Commission. The commission has received more than 1,800 public comments on the Reflect Orbital application and nearly 1,500 comments on the SpaceX filing. An ESO Institutional Affairs Office representative stated that the filings are now under FCC review and that the agency’s determinations will affect optical astronomy operations.