ANALYSIS OF THE MORNING TWILIGHT SKY BRIGHTNESS WITH SKY QUALITY METER

• Main Author: Annake H N, Laksmiyanti
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/42293
• Institution: Institut Teknologi Bandung

The transitional phenomena from night to morning due to Earth's rotation is known as dawn time. Observe the dawn phenomena means observing the sky brightness alteration from dark to light. The dawn time begins when the Sunlight has begun to be scattered by the upper atmosphere although the Sun's position is still below the horizon until it rises. For a long time, humans have observed and tried to understand the nature and behavior of the dawn process, especially about the Sun's position and the atmosphere’s complexity effect. The Sun’s depression angle measurement at early dawn is needed for practical purposes of the Fajr prayer time determining. Early dawn determining is observe the sky brightness alteration which accurately uses a photometer, named Sky Quality Meter (SQM). Observations were carried out in five different locations to obtain sky brightness values with varying heights and light pollution levels. There were in Imah Noong- Lembang, Tayu beach-Pati, Branta dock-Madura, Pengkol village-Pasuruan and e-Maya Observatory-Subang. Tayu beach represents a light pollution-free area while Branta dock is an area which affected by fishing boat lights. Imah Noong, Pasuruan, and e-Maya Observatory are suburban areas that are affected by settlements’ artificial light. Sky brightness was measured at time intervals per 1 and 10 seconds on certain days by observing weather conditions and the Moon phase. Data processing in sky brightness alteration determining using the gradient (slope) method or sky brightness alteration to time, the average value of different sky brightness in a certain period (moving average) and curve approximation (curve fitting). This is intended to obtain accurate results and a consistent method so that, it can be used in the next dawn sky brightness data processing. The results that are obtained using these methods series show the consistency of the dawn appearance time indication in each location. The time average of the dawn appearance based on 3? on Imah Noong at 4:53 a.m. or when the sun's depression angle was -16,40°, then in Tayu beach at 4:14 WIB; - 20,94°, Branta dock at 4:40 WIB; -14,39°, Pengkol village at 4:36 WIB; -16,21° and e-Maya Observatory at 4:52 WIB; -16.40°.