AST SpaceMobile deployed a 693-square-foot communications satellite into orbit called BlueWalker 3.
Astronomers say it's as bright as some of the brightest stars, and warn it could impact their work.
The company plans to orbit hundreds of others to provide a space-based broadband network.
In November, AST SpaceMobile unfurled an apartment-sized satellite complete with solar panels and a giant antenna into low Earth orbit.
It is now one of the brightest objects in the sky, outshining stars, the International Astronomical Union said in a statement last week.
The 693-square-foot satellite, BlueWalker 3, is designed to provide cell phone service from orbit to Earth. AST SpaceMobile bills it as the "largest-ever commercial communications array deployed in low Earth orbit."
It's one of more than 100 satellites the company plans to launch in the next two years in order to form a constellation-like fleet of satellites moving together.
The IAU shared images that show the bright trail the giant satellite leaves across the sky:
At its maximum brightness, the satellite was almost as bright as Antares and Spica - the 15th and 16th brightest stars in the night sky, respectively - according to observations from IAU astronomers.
Astronomers are also concerned about the potential for radio interference from these "cell phone towers in space," which the IAU warned could disrupt radio astronomy research.
"We are eager to use the newest technologies and strategies to mitigate possible impacts to astronomy," AST SpaceMobile said in a statement shared with Insider. "We are actively working with industry experts on the latest innovations, including next-generation anti-reflective materials."
"We are also engaged with NASA and certain working groups within the astronomy community to participate in advanced industry solutions, including potential operational interventions," the statement read.
Satellite debris can clog our view of the cosmos and create hazards for spacecraft
Over 5,500 satellites already litter low-Earth orbit, according to a recent report by the US's Government Accountability Office. Some estimates suggest 58,000 satellites will be launched by 2030, mostly driven by swarms of satellite constellations.
Leading the way is SpaceX, which already maintains more than 3,000 satellites and may top 12,000 in the coming decade to provide low-cost internet to remote locations.
The mounting number of satellites launched into orbit also adds to dicey close encounters that happen with other orbital debris, such as defunct satellites, hunks of rocket parts, and spacecraft. In October, the International Space Station had swerve to avoid collision with a piece of Russian satellite debris.
Astronomers are also concerned about how satellite constellations contribute to the loss to "humanity's ability to experience the natural night sky," according to the IAU statement.
Already, pristine night skies are diminishing due to light pollution from satellites and other human sources. A September 2021 study found that global light pollution from satellites increased by 49% from 1992 to 2017.
When we look up at night sky, many of the bright lights might not be stars - but satellites.