Analysis of sky brightness variations in full days based on sky quality meter measurement in Pekalongan

Abstract

The night sky brightness has an ecological impact, especially for nocturnal animals. Likewise, the shift from transition night to day and vice versa known as the fajr/dawn phase, has on impact on crepuscular animals. Continuous measurement are important in astronomy due to the impact of sky brightness. The sky brightness is slower to lighten at dawn and slower to darken at dusk which can be affected by light pollution sourced from human activities, meteorological, and natural factors (Moon phase and zodiacal light). Quantization of the sky brightness continuously in full days based on the function of light pollution, Sun position, and shadow length in the daytime are important to do. Analysis of the sky brightness at the limits of the beginning of dawn, the end of dusk, the sunrise/sunset, during mid-morning/evening, and the time of culmination are useful for testing the Islamic prayers time. Measurement of sky brightness in full days has been done using Sky Quality Meter photometer at coordinates 6˚50’42” southern latitude and 109˚37’55” eastern longitude for 25 days with 3 seconds retrieval resolution that installed neutral density variable and battery. Analysis of sky brightness data was carried out using Difference, Moving average, and Polynomial methods. This research concludes that the sky brightness during twilight shows relatively small variation, with the beginning of dawn identified at -15.301˚ of Sun elevation and the end of dusk at -18.853˚ of Sun elevation. The sky brightness profiles before and after 12 noon are asymmetrical. In the evening, the average difference in sky brightness at shadow lengths of 1 to 2 is 0.9 MPSAS with 0.39 standard deviation and the average shadow length of object during fluctuations is 1.36. The average difference in sky brightness at noon compared to midnight is 9.02 MPSAS.