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Drawing a Line in the Sky: Astronomers Confront Satellite Threat

The astronomy community has released recommendations for mitigating the impact of thousands of internet-providing satellites that companies plan to launch in the coming years.

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Drawing a Line in the Sky: Astronomers Confront Satellite Threat



CTIO/NOIRLab/NSF/AURA/DECam DELVE Survey Trails from 19 Starlink satellites were captured in this composite image taken in November 2019 by a camera on the Blanco 4-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile.

CTIO/NOIRLab/NSF/AURA/DECam DELVE Survey Trails from 19 Starlink satellites were captured in this composite image taken in November 2019 by a camera on the Blanco 4-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. ×

The sky is changing. As many astronomers and backyard onlookers have noticed, a number of unfixed “stars” have recently appeared. These moving blips are Starlink satellites, launched by the SpaceX corporation with the aim of providing high-speed internet to remote regions of the planet. Currently, about 600 Starlink satellites are in orbit, but SpaceX—as well as other companies—plan to fly many thousands more. These so-called satellite constellations could have a severe impact on astronomical observations. The astronomy community has now released recommendations for both the satellite industry and sky observers that could reduce the chances that a satellite “photobombs” a telescope image.

Astronomers have had to deal with satellites for decades. Around 5000 satellites are currently in orbit. Most are faint and travel along well-defined orbits, so astronomers can usually time an observation to avoid them or use software to remove their light from an image. But the problem took on a new magnitude when SpaceX launched its first bevy of Starlink satellites in March 2019. Sunlight reflecting off the satellites made them visible to the naked eye, with some observers reporting a “string of pearls” marching across the sky. “The brightness of the SpaceX satellites was a surprise to the entire astronomical community,” says Ralph Gaume, director of the astronomical sciences division at the National Science Foundation (NSF).

The satellites are so bright, in part, because they operate at 550 km above Earth. Most other communications satellites fly roughly 35,000 km above Earth in a geosynchronous orbit, but SpaceX chose low-Earth orbit to obtain a factor of 70 speedup in the time it takes internet signals to travel up to and back from the satellite. The company has approval for 12,000 satellites from the Federal Communications Commission, but it is looking to add 30,000 more. Other companies, such as Amazon and OneWeb, have announced plans to launch constellations of similar sizes. “An image with satellite trails happens occasionally now,” says Jeff Hall from Lowell Observatory in Arizona. “But with plans for 100,000-plus satellites, it’ll be happening almost all the time.”

To address this looming predicament, the American Astronomical Society (AAS) and the NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) organized the first Satellite Constellation Workshop in June 2020. Over 250 astronomers and industry…

Michael Schirber

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