What is satellite light pollution?
Satellite light pollution refers to the impact of sunlight reflected from low Earth orbit satellites on astronomical observations. LEO satellites at 500–600 km altitude are illuminated by the Sun even when the ground below is in twilight or darkness, appearing as bright streaks in long-exposure astronomical images. With thousands of satellites now in LEO — and plans for tens of thousands more — this has become a significant concern for professional and amateur astronomers worldwide.
The impact on astronomy
A single satellite crossing a 30-minute telescope exposure creates a bright streak that can obscure faint objects and contaminate data across many science programmes — from asteroid detection (critical for planetary defence) to deep field galaxy surveys and gravitational wave counterpart searches. The Vera C. Rubin Observatory's LSST survey, designed to image the entire sky every three nights in search of transient phenomena and near-Earth asteroids, is estimated to have 10–30% of images affected by satellite streaks without mitigation, based on current constellation plans.
Industry response
SpaceX deployed 'VisorSat' satellites with a deployable sun shade to reduce Starlink brightness; Starlink Gen2 has further darkened hardware and adjusted satellite orientation. OneWeb satellites were designed with reduced reflectivity. However, even with mitigations, the International Astronomical Union (IAU) and the UN Committee on the Peaceful Uses of Outer Space (COPUOS) found that no single technical mitigation is sufficient at mega-constellation scale. The ITU-established CPS (Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference), operated jointly with the IAU, coordinates technical guidelines and policy recommendations to protect radio astronomy and optical astronomy from satellite interference.