Variation of the Twilight Stages due to Sun Elevation: A Case Study in Malaysia

The major goal of this research is to pinpoint the exact start times of True (Real) Dawn and True (Real) Dusk inside the twilight intervals. When the white thread of diffused solar radiation appears on the eastern horizon, the True Dawn starts. The Real Dusk, on the other hand, occurs when the white thread of diffused sun radiation vanishes from the western horizon. For Muslims, knowing these hours is critical since they are the times of morning (Fajr) and evening (Esha’) prayers in Islam. As a result, the purpose of this research is to determine the altitude of the sun under the horizon at which both of the above-mentioned indications appear. In 2007 and 2008, the Sky Quality Meter (SQM) was utilised in four Malaysian locations to analyse the brightness at night, faux dawn, genuine dawn, true dusk, and pseudo dusk. During the whole monitoring period, the measurements were taken with the device oriented to the place of dawn and sunset at the horizontal angle of the sunrise or sunset and at five degrees slightly above the horizon. The sun’s height for actual dusk was determined to be -14.380.91, for the start of faux dusk it was found to be -14.860.91, and for the conclusion of pseudo dark it was found to be -17.80.7. While it was discovered that the genuine dawn began at -14.190.52 (with high confidence -14.71) and the faux dawn began at -18.620.82. The light magnitude of the whole night after the faux dark was found to be 20.770.93 mag./arcsec2, whereas the light magnitude before the pseudo dawn was found to be 22.17 0.1 mag./arcsec2. These findings corroborate numerous prior studies in this field and lead to the adoption of new sun vertical depression angle values for True Dawn (between 14.7 and 15) and True Dusk (between 14.7 and 15). (between 15 and 15.5).

Author(s) Details:

Yasser A. Abdel-Hadi,
Department of Solar and Space Research, National Research Institute of Astronomy and Geophysics (NRIAG), El-Marsad Street, P.O. 138, Helwan 11421, Cairo, Egypt.

A. H. Hassan,
Department of Solar and Space Research, National Research Institute of Astronomy and Geophysics (NRIAG), El-Marsad Street, P.O. 138, Helwan 11421, Cairo, Egypt.

Please see the link here: https://stm.bookpi.org/NTPSR-V4/article/view/6939

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