ESA Releases First Calibrated Color Night Mosaic of Europe from ISS Imagery

The European Space Agency (ESA) has introduced a high-fidelity nighttime mosaic of Europe, representing the first color composition derived from calibrated space-based imagery. This detailed visual product was compiled from over 7,000 photographs captured by astronauts aboard the International Space Station (ISS) throughout 2017. Until 2021, the ISS served as the primary orbital platform capable of producing such high-caliber, true-color visualizations of Earth’s nocturnal surface.

The spatial resolution achieved by the astronaut photography, reaching as fine as five meters per pixel, notably surpasses the typical capture capabilities of many contemporary Earth observation satellites. Dr. Alejandro Sánchez de Miguel, who led the 'Cities at Night' initiative, noted that much existing nighttime imagery of Europe relies on artistic renderings from monochrome data, lacking genuine spectral information. The 'Cities at Night' project utilized artificial intelligence algorithms alongside citizen science contributions to process the raw images and correct inherent optical distortions from acquisition.

Chromatic variations within the mosaic directly indicate the dominant lighting technology across different European areas. Regions displaying warmer, reddish hues generally correlate with older-generation sodium vapor light sources. Conversely, areas illuminated with whiter and bluer light signify the broad adoption of modern Light-Emitting Diode (LED) fixtures in street lighting. This shift to a whiter, bluer spectrum is a scientific concern, as experts caution that its expansion erodes natural nocturnal cycles, presenting ecological and physiological challenges by influencing circadian rhythms.

Scientific investigations have identified three principal detrimental outcomes associated with this trend: the suppression of the sleep-regulating hormone melatonin, adverse behavioral reactions in insects and bats, and a reduction in the visibility of celestial objects. Dr. Sánchez de Miguel emphasized the historical value of this calibrated material, stating it offers a significant opportunity to retrospectively analyze light pollution levels preceding the era of color-sensitive satellites. The announcement of this mosaic in late 2025 confirms its immediate utility for current environmental monitoring and research.

The high resolution of astronaut imagery contrasts with lower-resolution satellite data, such as the Visible Infrared Imaging Radiometer Suite Day-Night Band (VIIRS DNB), which typically offers around 750 meters resolution. The 'Cities at Night' project, engaging citizen scientists through stages like 'Dark Skies' and 'Lost at Night,' aims to catalog and georeference nearly half a million photographs to map the Earth at night in true color. This effort is critical as global nighttime brightness has increased by approximately 10% annually over the last decade. Furthermore, the adoption of LEDs, intended for energy savings, has sometimes caused a 'rebound' effect, increasing overall illumination and contributing to greater light pollution globally between 2012 and 2015 in nearly 60 countries by 110 to 150 percent. The illumination from street lighting in the European Union territory alone was previously estimated to cost €6.8 billion annually, highlighting the economic and ecological dimensions of this research.