Typology of dawn light curves in high and low light pollution areas

Abstract

Based on visual observations, the emergence of dawn can be grouped into three groups which are influenced by the zenith distance of the Sun, namely: astronomical dawn (Z = 108°), nautical dawn (Z = 102°), and civil dawn (Z = 96°). Observation of the dawn light intensity at two locations (Banyuwangi and Semarang) with different light pollution levels using the SQM (Sky Quality Meter) intensity probe produces a light curve with similarities. Based on the plot of several dawn light curves, we performed an analysis by performing curve analysis. We found that the appearance of astronomical dawn, nautical dawn, and civil dawn can be marked using the dawn light curve. The light curve plots from two different observation locations show that the three dawn groups' appearance has a diverse range of sky brightness values. The average value of sky brightness for each dawn measured by SQM in low and high light pollution areas is different. Namely 21.09 ± 0.02 mpsas and 17.06 ± 0.06 mpsas (astronomical dawn), 17.13 ± 0.14 mpsas and 16.94 ± 0.13 mpsas (nautical dawn), and 10.27 ± 0.07 mpsas and 12.54 ± 0.61 mpsas (civil dawn). Based on the results of the analysis of the dawn typology, the emergence of dawn Sadiq (an early marker of dawn prayer time) can be analyzed using a linear function approach to light intensity before the appearance of astronomical dawn. The dawn light curve analysis results from two different locations show that dawn appears at an average height of -20.01 ± 0.5 degrees and -13.12 ± 0.73 degrees for observations in low and high light pollution areas.