A satellite threatening to outshine the stars has astronomers worried
Trails in the night sky left by BlueWalker 3 are juxtaposed against the Nicholas U. Mayall 4-metre Telescope at Kitt Peak National Observatory in Arizona.
Scientists with the International Astronomical Union are warning that a recently launched commercial satellite has become one of the brightest objects in the night sky, posing a problem for astronomers and casual stargazes alike. And they say the object is likely to be the first of many.
The company AST SpaceMobile launched its BlueWalker 3 communications satellite on Sept. 22 last year to an altitude of about 500 kms. Six weeks later, it deployed an antenna array with an area of 64 square metres, roughly the size of a highway billboard. In April, the company made the first space-based two-way phone call with unmodified smartphones using the satellite.
But astronomers were quick to take note, pointing out that the satellite’s large size and low orbit made it a particularly bright object in the night sky, making it more difficult to image dimmer stars.
What’s more, its transmission technology threatens to overlap frequencies used by radio astronomers, who filed a complaint with the Federal Communications Commission in the U.S. It has granted an experimental license to BlueWalker 3, but still hasn’t approved the company’s proposal for a fleet of 168 even larger satellites it calls BlueBirds.
The number of BlueBirds is dwarfed by SpaceX’s Starlink satellites, which number in the thousands. But those are significantly smaller, and newer models have been designed to reduce the glare they produce while in orbit.
The company AST SpaceMobile launched its BlueWalker 3 communications satellite on Sept. 22 last year to an altitude of about 500 kms. Six weeks later, it deployed an antenna array with an area of 64 square metres, roughly the size of a highway billboard. In April, the company made the first space-based two-way phone call with unmodified smartphones using the satellite.
But astronomers were quick to take note, pointing out that the satellite’s large size and low orbit made it a particularly bright object in the night sky, making it more difficult to image dimmer stars.
What’s more, its transmission technology threatens to overlap frequencies used by radio astronomers, who filed a complaint with the Federal Communications Commission in the U.S. It has granted an experimental license to BlueWalker 3, but still hasn’t approved the company’s proposal for a fleet of 168 even larger satellites it calls BlueBirds.
The number of BlueBirds is dwarfed by SpaceX’s Starlink satellites, which number in the thousands. But those are significantly smaller, and newer models have been designed to reduce the glare they produce while in orbit.
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A group of astronomers have penned an article in the journal Nature, titled “The high optical brightness of the BlueWalker 3 satellite,” for which they enlisted a team of amateur and professional astronomers from Chile, the U.S., Mexico, New Zealand, the Netherlands and Morocco to make observations of the night sky.
“Large constellations of bright artificial satellites in low Earth orbit pose significant challenges to ground-based astronomy,” the study’s authors wrote. Their team calculated that BlueWalker 3 reached a brightness on par with Procyon and Achernar, two of the 10 most luminous stars in the sky.
And while AST SpaceMobile has said it will look into ways of reducing the brightness of future satellites, the Nature article notes that “the trend towards the launch of increasingly larger and brighter satellites continues to grow.”
Such objects can impede astronomical data by “streaking” through images taken from the ground, and even those taken by space telescopes like the Hubble that orbit below many of the communications satellites. They can cover up stars and other targets that astronomers want to see. And they can even outshine dimmer stars with their cumulative brightness, as they grow in number.
The BlueWalker 3 satellite is seen in a clean room at AST SpaceMobile prior to launch.
© AST SpaceMobile
Even more alarming is that bright satellites could endanger not just astronomy but early warnings of an asteroid impact, by getting in the way of observations made around twilight.
“These observations look towards the inner solar system and so need the sun just below the horizon,” Jeremy Tregloan-Reed, co-author of the study, told space.com . “One such type of observation looks for near-Earth objects and provides an early warning to potential asteroids on a collision course with Earth. Hence, these satellites could hinder any attempt of an early warning and so prevent us from protecting ourselves from an extinction level impact.”
Michael J.I. Brown, an associate professor in astronomy at Monash University in Melbourne, sounded a more whimsical note in an article for the website The Conversation . “The night sky is a shared wilderness,” he wrote. “On a dark night, away from the city lights, you can see the stars in the same way as your ancestors did centuries ago. You can see the Milky Way and the constellations associated with stories of mythical hunters, sisters and journeys. But like any wilderness, the night sky can be polluted.”
He ended his article with a question: “Will the night sky be cluttered with bright artificial satellites for the sake of internet or 5G? Or will we pull back and preserve the night sky as a globally shared wilderness?”
Even more alarming is that bright satellites could endanger not just astronomy but early warnings of an asteroid impact, by getting in the way of observations made around twilight.
“These observations look towards the inner solar system and so need the sun just below the horizon,” Jeremy Tregloan-Reed, co-author of the study, told space.com . “One such type of observation looks for near-Earth objects and provides an early warning to potential asteroids on a collision course with Earth. Hence, these satellites could hinder any attempt of an early warning and so prevent us from protecting ourselves from an extinction level impact.”
Michael J.I. Brown, an associate professor in astronomy at Monash University in Melbourne, sounded a more whimsical note in an article for the website The Conversation . “The night sky is a shared wilderness,” he wrote. “On a dark night, away from the city lights, you can see the stars in the same way as your ancestors did centuries ago. You can see the Milky Way and the constellations associated with stories of mythical hunters, sisters and journeys. But like any wilderness, the night sky can be polluted.”
He ended his article with a question: “Will the night sky be cluttered with bright artificial satellites for the sake of internet or 5G? Or will we pull back and preserve the night sky as a globally shared wilderness?”
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