An international group of astronomers has reported on the brightness of the 5G satellite, named BlueWalker 3, which is currently being tested to transmit 4G and 5G signals directly from satellites to mobile phones. When the satellite begins to unfold its antenna, it becomes the brightest object in space at the moment.
The brightness of stars in space is measured on a magnitude scale, with lower numbers indicating brighter objects. For example, the sun has a magnitude of -27, the International Space Station has a magnitude of -6, Venus has a magnitude of -4.6, while the North Star has a magnitude of +2.
BlueWalker 3 satellite was launched into orbit in September 2022. One of its unique features is its large antenna panel. When the satellite deploys its antenna panel, it becomes bright with a magnitude of +0.4. However, the International Astronomical Union of astronomers has requested low-orbit satellite companies to limit their brightness to +7, in order to minimize interference with astronomical observations.
Having a few bright objects in orbit may not be a significant issue. However, there is a growing trend towards launching a large number of satellites, similar to SpaceX’s Starlink, to provide direct communication to mobile devices. The first version of Starlink had a brightness of +5.1 but was criticized for interfering with astronomical imaging. This led to the development of DarkSat, which had a brightness of +7.3. However, it faced issues with heat dissipation, resulting in the creation of VisorSat, which has a brightness of +6.0.
TLDR: An international group of astronomers has reported that the BlueWalker 3 satellite, currently being tested for 5G communication, becomes the brightest object in space when it deploys its large antenna panel. While having a few bright objects in orbit may not be a problem, the increasing number of satellites, such as Starlink, has raised concerns about interference with astronomical observations.