A new study published in Nature reveals that BlueWalker 3, a test satellite launched on September 10, 2022, shines as brightly as the brightest stars in the constellations of Canis Minor and Eridanus. This intense brightness has posed significant challenges for astronomers using ground-based telescopes to explore the night sky.
BlueWalker 3 boasts a considerable size, measuring 693 square feet, and relies on a large phased-array antenna to harness power from space and deliver cellular broadband directly to mobile phones. Its reflectivity and size make it a prominent object in the night sky, rivaling even the brightest celestial objects.
Siegfried Eggl from the University of Illinois at Urbana-Champaign explained that amateur astronomers initially raised concerns about BlueWalker 3’s potential brightness, prompting international observers to capture the satellite when it deployed its 64 square meter phased-array antenna. This deployment, reflecting sunlight, made it one of the most luminous objects visible in the night sky.
The presence of such bright satellites poses a challenge for radio astronomy, introducing additional noise into observations. Eggl likened bright satellites in the telescope’s field of view to staring at the sun without sunglasses, further complicating astronomers’ work.
To assess the impact of this satellite’s brightness on radio astronomy, Eggl and professional astronomers from various countries conducted an international observing campaign. Pre-deployment observations had suggested that BlueWalker would be exceptionally bright. Telescopic observations confirmed this, indicating that the satellite’s brightness increased significantly, from approximately +6 to +0.4. This level of brightness compares to Procyon and Achernar, the brightest stars in the Canis Minor and Eridanus constellations, respectively. To put it in perspective, the unaided eye at a dark sky site can see stars with a magnitude of +6.
Eggl noted that the size of the satellite plays a crucial role in determining its brightness, as larger objects can reflect more sunlight toward Earth. Predicting brightness is a complex task due to satellites’ continuous changes in position, altitude, and material properties, affecting how they reflect light in various directions.
Despite numerous efforts by the aerospace industry, policymakers, and astronomers to mitigate the impact of satellites on radio astronomy, challenges persist. Companies like SpaceX have already launched thousands of satellites, with plans for thousands more. These satellites, if as bright as current constellation satellites, could significantly alter the night sky, making astronomical observations increasingly difficult, particularly during the early and late hours of the night when satellites are most likely to reflect sunlight.
The study underscores the growing trend of launching larger and brighter satellites into orbit, emphasizing the importance of understanding how these satellites reflect sunlight. Collaborative efforts between researchers and satellite operators can help develop more effective mitigation strategies to minimize the disruption of scientific observations and preserve the sanctity of the night sky.