UBVRI night sky brightness at Kottamia Astronomical Observatory

Photoelectric observations of night sky brightness (NSB) at different zenith distances and azimuths, covering all the sky, at the Egyptian Kottamia Astronomical observatory (KAO) site of coordinates ϕ = 29° 55.9' N and λ = 31° 49.5' E, were done using a fully automated photoelectric photometer (FAPP). The Bessel wide range system (UBVRI) is used for the first time to observe NSB for three consecutive nights (1-3 August, 2022) under good seeing conditions after the moon sets. The deduced results were taken in photons and converted into mag/arcsec². The average zenith sky brightness for U, B, V, R and I filters are found to be 20.49, 20.38, 19.41, 18.60 and 17.94 mag/arcsec² respectively. The average color indices (U-B), (B-V), (V-R) and (R-I), at the zenith are detected to be 0.11, 0.98, 0.81 and 0.66, respectively. We plotted the isophotes of the sky brightness at KAO in U, B, V, R and I colors (filters) and determined both the average atmospheric extinction and sky transparency through these UBVRI filters. The atmospheric and other meteorological conditions were taken into our consideration during the observational nights. The results of the current study illustrate the main impact of the new cities built around KAO on the sky glow over it, and which astronomical observations are affected.