The First Dark Sky Map of Thailand: International Comparisons and Factors Affecting the Rate of Change

We present the first dark sky map of Thailand using calibrated zenith artificial night-sky brightness from VIIRS satellite data covering 2012–2023. Results were compared with the United Kingdom, Chile, and Botswana to provide international context. Maps identified 14 classes of dark-sky areas, ranging from pristine sky to cone cell stimulation, with classes 1–9 designated as “potential” dark sky. Influencing factors—including population, GDP, inflation rate, unemployment, time, and country name—were analyzed using mathematical models. The number of potential dark-sky areas was best predicted by a Decision Tree model with a relative error of 0.4% ± 0.3%. Risk assessment suggests that Thailand’s potential dark-sky areas are significantly threatened and could disappear by 2068 without conservation. Since 2012, Thailand has lost 15.4% of its pristine skies, while the UK gained 0.8%. Botswana remained nearly stable (–0.7%), outperforming Chile (–5.3%). By 2023, ~60% of Thai residents had lost naked-eye visibility of the Milky Way, and one-fifth were exposed to very high nighttime light intensities, preventing dark adaptation. These findings highlight Thailand’s rapid dark-sky degradation and emphasize the value of satellite-based monitoring for conservation strategies, sustainable development policies, and international efforts to protect the natural night environment.