The number of working satellites has soared in the past five years to around 11,000, mostly because of constellations of orbiters that provide Internet connectivity around the globe. Just one company, SpaceX in Hawthorne, California, has more than 7,000 operational Starlink satellites, all launched since 2019; OneWeb, a space communications company in London, has more than 630 satellites in its constellation. On paper, tens to hundreds of thousands more are planned from a variety of companies and nations, although probably not all of these will be launched.

Satellites interfere with ground-based astronomical observations, by creating bright streaks on images and electromagnetic interference with radio telescopes. The satellite boom also poses other threats, including adding pollution to the atmosphere…

Before the launch of Starlinks, astronomers had no centralized reference for tracking satellites. Now, the International Astronomical Union (IAU) has a virtual Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS), which serves as an information hub…One of the centre’s tools, called SatChecker, draws on a public database of satellite orbits, fed by information from observers and companies that track objects in space. Astronomers can use SatChecker to confirm what satellite is passing overhead during their observations…Tools such as SatChecker help telescope operators avoid problems by allowing them to target a different part of the sky when a satellite passes overhead or by simply pausing observations as it flies by. It would aid astronomers if SatChecker had even more accurate information about satellite positions, but there are constraints on improving the system. SatChecker data come from the US Space Force, which draws on a global network of sensors that tracks objects in orbit and issues updates on satellite locations as often as several times a day. The frequency of these updates is limited by factors such as how often a sensor can observe an object and whether the sensor can distinguish what it’s looking at.

Excerpts from   Alexandra Witze, Swarms of satellites are harming astronomy. Here’s how researchers are fighting back, Nature, Mar. 18, 2025