A Sky Brightness Contrast Measurement before Sunrise and after Sunset over a Baghdad Region, Iraq

Abstract

In this work, an analytical study had been made of sky brightness variations using a photometer of Sky Quality Meter (SQM-LU). The sky brightness measurements were performed in Baghdad city of Iraq (Latitude: 33°20’N, Longitude: 44°23’E, and Altitude: 34m above sea-level). The values of sky brightness level were collected on 27 December 2019 as well as 10 January 2020 at sunrise and sunset. The aim of this research is to study on sky illumination contrast by taking moonlight (moonless/full moon) as a reference source. Additionally is to localize the direction of the sun during both sunrise and sunset. The results indicated that, in case of sunrise and moonless, the sky brightness level was obtained averagely at 13.60 ± 0.26 magnitude/arcsecond2 with sun’s altitude angle at -9.79° ± 0.12°. While, in case of sunrise and full moon, the sky brightness level was obtained averagely at 12.75 ± 0.25 magnitude/arcsecond2 with sun’s altitude angle at -8.87° ± 0.11°. Findings also showed that, in case of sunset and moonless, the sky brightness level was obtained averagely at 17.44 ± 0.26 magnitude/arcsecond2 with sun’s altitude angle at -10.66° ± 0.12°. While, in case of sunset and full moon, the sky brightness level was obtained averagely at 15.69 ± 0.25 magnitude/arcsecond2 with sun’s altitude angle at -10.25° ± 0.11°. In conclusion, the study shows a correlation between the sky brightness magnitude against sun’s altitude angle, moon’s phase, and weather conditions as well.