The Effect of Sun Elevation on the Twilight Stages in Malaysia

Abstract

This study is concerned with determining the altitude of the sun under the horizon to the beginning and the end of the true and pseudo dawn and dusk. In 2007 and 2008, the Sky Quality Meter (SQM) was used in four regions in Malaysia to measure the brightness at night, pseudo dawn, true dawn, true dusk and pseudo dusk. The measurements were taken when the device was directed to the position of sunrise and sunset at the horizontal angle of the sunrise or sunset and at five degrees above the horizon during the entire monitoring period. The altitude of the sun for the true dusk was found to be -14.38° ± 0.91° and for the beginning of the pseudo dusk was found to be -14.86° ± 0.91° and the end of the pseudo dusk is -17.8° ± 0.7°, while for the beginning of the true dawn it was found to be -14.19° ± 0.52° (for high confidence -14.71°) and for the pseudo dawn was found to be -18.62° ± 0.82°. The light magnitude of the full night after the pseudo dusk was found to be 20.77 ± 0.93 mag./arcsec2, while it was found to be 22.17 ± 0.1 mag./arcsec2 before the pseudo dawn.