The number of orbiting satellites is growing exponentially. Not only do these artificial stars threaten to compromise our view of a night sky untouched by human engineering, but the light they reflect has measurably increased the brightness of that sky. As of Jan. 1, 2021 there were 3,372 operating satellites in orbit, the vast majority launched by public and private entities in the U.S. There are also tens of thousands of booster rockets, non-operational satellites and space debris resulting from satellite collisions and other sources.

Astronauts aboard the space station photographed the southern lights (aurora austrinus) and a train of 16 Starlink satellites over the Southern Ocean off the coast of Antarctica. (NASA)
Astronauts aboard the space station photographed the southern lights (aurora austrinus) and a train of 16 Starlink satellites over the Southern Ocean off the coast of Antarctica. (NASA)

Much of the recent rapid rise in numbers originates from SpaceX, an aerospace manufacturer headquartered in California. Since May 2019 the private business has placed more than 1,320 Starlink satellites in orbit with the goal of offering high-speed internet service across the planet. When its "mega-constellation" of satellites is completed in 2027 that number will increase to 12,000. The permitting process for an additional 30,000 Starlinks that would further expand service is already in the pipeline.

This 333-second exposure taken last year by the Dark Energy Camera at Cerro Tololo Inter-American Observatory shows 19 streaks attributed to Starlink satellites passing through the camera’s field-of-view shortly after launch. (NSF’s National Optical-Infrared Astronomy Research Laboratory/NSF/AURA/CTIO/DELVE)
This 333-second exposure taken last year by the Dark Energy Camera at Cerro Tololo Inter-American Observatory shows 19 streaks attributed to Starlink satellites passing through the camera’s field-of-view shortly after launch. (NSF’s National Optical-Infrared Astronomy Research Laboratory/NSF/AURA/CTIO/DELVE)

To its credit, the company has worked with astronomers to mitigate the satellites' brightness, though with limited success. Many of them are still faintly visible with the naked eye. And if you and I can see them, imagine the nuisance they are to astronomers trying to collect the light of dim and distant galaxies. For us, they come and go, but in long time-exposure images each satellite produces a permanent streak of light.

WDAY logo
listen live
watch live
Newsletter signup for email alerts

Natural airglow — the pale pink and green streaks in the photo — is only visible under the darkest skies. Molecules in the upper atmosphere absorb ultraviolet (UV) light from the sun during the day and then release that energy as faint swaths of green, red and yellow light at night. (Bob King)
Natural airglow — the pale pink and green streaks in the photo — is only visible under the darkest skies. Molecules in the upper atmosphere absorb ultraviolet (UV) light from the sun during the day and then release that energy as faint swaths of green, red and yellow light at night. (Bob King)

A new report by scientists based in Slovakia, Spain and the U.S. finds that objects orbiting Earth elevate the brightness of the night sky by at least 10 percent over natural light levels. The satellites produce a "skyglow effect" from the combined sunlight they reflect and scatter across the planet's night skies. The amount exceeds a threshold adopted by astronomers in 1979 to determine whether a location is considered light-polluted.

Trails left by SpaceX Starlink satellites are seen in this time exposure taken on April 20, 2020 from Berlin, Germany. (Andreas Möller / CC BY-SA 4.0)
Trails left by SpaceX Starlink satellites are seen in this time exposure taken on April 20, 2020 from Berlin, Germany. (Andreas Möller / CC BY-SA 4.0)

The result surprised even Dr. Miroslav Kocifaj (Slovak Academy of Sciences and Comenius University), who led the study. Kocifaj assumed that satellites would contribute only marginally to sky brightness. But when the group modeled how much light working satellites and human-generated space debris produced by factoring in the objects' known sizes and brightness they found otherwise. Unfortunately, as the number of orbiting vehicles continues to increase so will the percentage and extent of artificial skyglow.

While brighter satellites are visible as artificial "stars" that move across the sky there are a host of fainter objects we can't directly see that contribute to a faint, diffuse night illumination. Unlike local types of light pollution like a shopping center or new apartment complex, satellite glow adds to sky brightness across much of the Earth. In addition to light pollution the rapid increase in their number increases the probability of collisions, which would contribute even more material.

This graph plots the number of all objects in Earth orbit officially cataloged by the U.S. Space Surveillance Network as of 2019. The sharp rise in 2007 occurred after China intentionally destroyed one of its aging weather satellites during a 2007 anti-satellite test. (U.S. National Aeronautics and Space Administration Orbital Debris Program Office)
This graph plots the number of all objects in Earth orbit officially cataloged by the U.S. Space Surveillance Network as of 2019. The sharp rise in 2007 occurred after China intentionally destroyed one of its aging weather satellites during a 2007 anti-satellite test. (U.S. National Aeronautics and Space Administration Orbital Debris Program Office)

For those who are passionate about preserving the night sky how might we mitigate this growing problem? Obviously, the cat's already out of the bag. We'll need to talk with those who represent us in Congress to make them aware of the issue and stress the importance of crafting guidelines and standards for current and future satellite constellations. You can find and contact your representative(s) on the Find Your Representative site. Limits need to be set on size, reflectivity and (hopefully) sheer numbers before it's too late. Otherwise we not only stand to sacrifice the peace and tranquility of a night under the stars but also astronomical research and what it reveals about the nature of the universe.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.