International Journal of Astronomy and Astrophysics, 2022, 12, 7-29 https://www.scirp.org/journal/ijaa ISSN Online: 2161-4725 ISSN Print: 2161-4717 DOI: 10.4236/ijaa.2022.121002 Feb. 11, 2022 7 International Journal of Astronomy and Astrophysics The Effect of Sun Elevation on the Twilight Stages in Malaysia Yasser Abdel-Fattah Abdel-Hadi, Amir Hussein Hassan Solar and Space Research Department, National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, Egypt 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 con- fidence −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./arcsec 2 , while it was found to be 22.17 ± 0.1 mag./arcsec 2 before the pseudo dawn. Keywords Twilight, Light Magnitude, Altitude of the Sun, Beginning of the True Dusk, Beginning of the True Dawn, Pseudo Dusk, Pseudo Dawn, Full Night, SQM 1. Introduction The study of the twilight of various types is extremely important for large seg- ments of the society, especially astronomers, to study the planets during the twi- light for the length of the twilight in the summer months in the upper latitudes [1]. When the sun reaches a depression of 10˚ - 15˚ below the horizon, the in- trinsic glow of the upper atmospheric layers begins to appear together with star- How to cite this paper: Abdel-Hadi, Y.A.-F. and Hassan, A.H. (2022) The Effect of Sun Elevation on the Twilight Stages in Malay- sia. International Journal of Astronomy and Astrophysics, 12, 7-29. https://doi.org/10.4236/ijaa.2022.121002 Received: November 7, 2021 Accepted: February 8, 2022 Published: February 11, 2022 Copyright © 2022 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access