Searching potential astronomical sites in Ethiopia

This work aims to choose potential astronomical sites that can be candidates for a new astronomical optical observatory in Ethiopia, in addition to the Entoto Observatory and Lalibela sites. For our primary investigation, the six basic criteria, namely the altitude of the mountains, artificial light pollution, cloud coverage, humidity, wind speed, and wind direction, are taken into account. Consequently, using the multi-criteria statistical analysis (MCSA) techniques, 21 high-potential places are selected and presented for further investigation out of 367 mountains. Those selected mountains are mapped and presented to study the future of the astronomical seeing effect. This study may contribute to the protection of those potential astronomical sites and their dark skies and the development of astrotourism for the sustainable development of modern astronomy in Ethiopia and in the East African region.

💡 Research Summary

The paper addresses the need for additional optical astronomical observatories in Ethiopia, a country that already hosts two sites (Entoto and Lalibela) but faces increasing light‑pollution pressures from urban expansion. The authors adopt a systematic, data‑driven approach that combines Multi‑Criteria Decision Analysis (MCDA) with Multi‑Criteria Statistical Analysis (MCSA) to evaluate the suitability of high‑altitude locations across the nation.

First, they compiled a list of 367 mountains with elevations above 2,500 m, recognizing that higher altitude generally reduces atmospheric column density and improves seeing conditions. Six primary criteria were selected: (1) altitude, (2) artificial light pollution (quantified via night‑sky brightness and distance from cities of varying sizes), (3) cloud cover (expressed as the percentage of clear nights per year), (4) relative humidity, (5) wind speed, and (6) wind direction. Data were sourced from publicly available satellite and geospatial platforms—NASA POWER, FAO, Weather Spark, SRTM—and supplemented with on‑site observations for infrastructure and local light‑pollution assessments.

The authors categorized Ethiopian settlements into six tiers (from capital‑city size to villages) and calculated the distance from each mountain to the nearest settlement, establishing a light‑pollution index that penalizes sites close to larger urban centers. Cloud‑cover thresholds were set to favor locations with at least 45 %–68 % clear nights (approximately 110–140 clear nights annually). Humidity was constrained to the 30 %–70 % range to limit atmospheric turbulence, while wind speed was required to be below 10 m s⁻¹ with a relatively stable prevailing direction.

Each criterion was normalized, weighted according to its impact on astronomical observations, and aggregated into a composite suitability score. The ranking process reduced the initial pool to 46 sites after applying the cloud‑cover filter, then to 32 after humidity screening, and finally to 21 sites after incorporating wind considerations. These 21 sites, together with the two existing observatories, are presented in a table and mapped in Figure 1. The table lists altitude, cloud‑percentage, light‑pollution level, humidity, wind speed, and a qualitative suitability rating (e.g., “Highly Suitable”, “Very Highly Suitable”).

The discussion acknowledges that the current analysis omits several important factors—seismic risk, aerosol optical depth, precipitable water vapor (PWV), and infrastructure accessibility—which the authors plan to integrate in a subsequent phase. Moreover, they intend to conduct on‑site “seeing” measurements (quantifying atmospheric turbulence) for each of the 21 candidate mountains to validate the remote‑sensing based rankings.

The study’s broader significance lies in providing a reproducible framework for astronomical site selection in data‑scarce regions, contributing to the preservation of dark‑sky areas, and fostering astrotourism as a component of sustainable development in Ethiopia and the wider East African region. By coupling satellite‑derived climatological metrics with a transparent multi‑criteria methodology, the authors lay the groundwork for future investments in ground‑based astronomy that are scientifically justified and environmentally responsible.