Observation of the true dawn for three different countries in the Arab region

Abstract

The study of the phenomenon of true dawn, a critical component of morning twilight, has great importance for Muslims (who constitute nearly a quarter of the world’s population) and for astronomy in general, especially in viewing celestial bodies during the twilight period. Observation with the naked eye is of utmost importance in monitoring celestial phenomena and bodies during the hours of night and twilight, and it also serves as a basic reference for the light magnitude calculation. This research involved naked-eye observations of true dawn across three distinct desert locations with varying climates but similar latitudes. One location also included concurrent camera observations. In Riyadh (KSA), the true dawn was observed to progressively spread and expand from the point of solar depression (Do) of 14.6 degrees (where Do represents the negative solar altitude), with the horizontal azimuth widening until the dawn light reaches the range of WAZ=80˚. The color gradation intensity of light during true dawn is red > green > blue, the false dawn is at Do = 18.58°±0.85, while the true dawn is at Do = 14.88° (14.58°±0.3). The false dawn was observed at Do =18.58˚ ± 0.85 and the true dawn occurred at Do =14.58˚± 0.3. On the 15th of May City, Egypt, the true dawn was observed at a solar depression (Do) of 12.69° (11.88° ± 0.81°). This observation was influenced by reduced horizontal visibility due to wind direction from the city of Helwan. Observations conducted in two adjacent desert locations in Mauritania revealed a true dawn onset at Do = 14.85° (14.24° ± 0.61°). Under optimal conditions, characterized by excellent visibility (full moonlight and phase of the moon around, f ≈ 1), the true dawn onset in locations such as Riyadh, Mauritania, and Aswan, Egypt, was observed to occur at approximately Do ≈ 14.4°.