Investigation Of Twilight Using Sky Quality Meter For Isha’ Prayer Time

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Investigation Of Twilight Using Sky Quality Meter For Isha’ Prayer Time

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  Investigation Of Twilight Using Sky Quality Meter For Isha ’ Prayer Time   INTRODUCTION Early studies done by astronomers such as IbnMu c ādh , al- Bīrūnī  , al- Qāyinī  , IbnYūnus  etc. [1, 2]. Ibn al- Shā ir adopted various value for each prayer times such as 17 o  for Isha ’  due to their asymmetry property [3]. There are many efforts made on sky twilight measurement using a photometer and a CCD camera, yet they are not specific on prayer times determination [4-6]. In this paper, we show that elusive light can be detected i.e. shafaq al-abyad    ̣  [7]. The elusive light is detected when Sun dip below horizon. The important of knowing angle of elusive light solely for determination of two prayer times i.e. Isha ’  and Subh. Based on that, we investigated Isha ’  prayer time using Sky Quality Meter (SQM). INSTRUMENTATION PERFORMANCE  In order to understand the measurements, it was tested and characterized by checking the acceptance angle, linearity and spectral responsivity [8] by running photoelectric effects experiments [7]. A trough is formed on the graph as evidence of SQM characteristic to behave when certain colours (wavelength) strike on its sensor. Both values have a high correlation and clearly when twilight colours (lower wavelength colours) hit the sensor, it consistently gives high readings  –  see FIGURE 1. The obtained response curve of SQM multiplying the spectral responsivity of the TAOS TSL237 photodiode by the transmittance of the Hoya CM-500 filter. EXPERIMENTAL PROCEDURES The brightness of twilight sky observations were carried out from May 2007 until April 2008 intermittently in accordance of photometric night. We choose two (2) sites in Malaysia with certain qualities, 1) best obstruction-free horizon and 2) the least light-pollution surrounding. It was carried out in the city peripheral of Kuala Lipis (Pahang) and Port Klang (Selangor). We took appropriate measure for every phase i.e. pre-observation, observation and post-observation [7]. The measurements were covered between 400-700 nm in accordance of human eyes and SQM range. Data were taken in two minutes interval. RESULT AND DISCUSSION  For Isha ’,  receipt of light is measured in terms of increase in magnitude values (decreasing of light). By plotting the magnitude values against time, a characteristic growth curve can be observed. The curve is divided into three (3) phases. The first phase is slow growth which means there was still bright light even the Sun just set. In the second phase shows a minimum of two gradual acclivities is increase at the certain rate. The gradual acclivity demonstrates receipt of light when the Sun is at certain degrees below horizon (6 o  and 12 o ). The third stage is the stationary phase when growth stops and no increase in magnitude values for a period of time and this prove the beginning of Isha ’  is indicated by a formed plateau  –  see FIGURE 2  –  FIGURE 3.   CONCLUSION From the evidence, SQM is able to assist the process of determining the beginning of Isha ’ . It is plausible that the value of twilight angle is fluctuating between for Isha ’  according what is given by the instrument. ACKNOWLEDGMENTS The authors wish to thank IPPP of University of Malaya for financial assistance. REFERENCES 1. King, D.A., Call of the Muezzin: (Studies I-IX) . 2004, Leiden: E.J. Brill. 2. King, D.A., In Synchrony with the Heavens, Studies in Astronomical Timekeeping and Instrumentation in Medieval Islamic Civilization . Vol. 2. 2005, Leiden: E.J. Brill. 3. Goldstein, B.R., Theory and Observation in Ancient and Medieval Astronomy  . 1985, London Variorum. 4. Chiplonkar, M.W. and P.V.L. Kulkarni, Seasonal Variation of Twilight Intensity.  Czechoslovak Academy of Science, 1959. 10 . 5. Ugolnikov, O.S., O.V. Postylyakov, and I.A. Maslov, Effects of Multiple Scattering and Atmospheric  Aerosol on the Polarization of the Twilight.  Journal of Quantitative Spectroscopy & Radiative Transfer, 2004. 88 . 6. Tyson, N.D. and R.R. Gal,  An Exposure Guide for Taking Twilight Flatfields with Large Format CCDs.  The Astronomical Journal, 1993. 105 (3). 7. Shariff, N.N.M., Sky Brightness at Twilight: Detectors Comparison between Human Eyes and Electronic Device For Isha' and Subh from Islamic and Astronomical Considerations , in Science and Technology Studies . 2008, University of Malaya: Kuala Lumpur. 8. Cinzano, P., Night Sky Photometry with Sky Quality Meter  , in ISTIL Internal Report  . 2005, ISTIL (Instituto di Scienza e Tecnologia dell'Inquinamento Luminoso): Italy. SQM/AltitudeofSun vsTime-25-20-15-10-50510152025    1   9  :   1   0   1   9  :   1  4   1   9  :   2   0   1   9  :   2  4   1   9  :   3   2   1   9  :   3   8   1   9  :  4   6   1   9  :   5   0   1   9  :   5  4   1   9  :   5   8   2   0  :   0   2   2   0  :   0   6   2   0  :   1   0   2   0  :   1  4   2   0  :   1   8   2   0  :   2   2   2   0  :   2   6   2   0  :   3   0   2   0  :   3  4   2   0  :   3   8 Time    S   Q   M    /   A    l   t   i   t   u   d   e   o    f   S   u   n SQMAltitudeofSun PlateauSQM: 20:28Official timeof  Maghrib : 19:13Official timeof  cIsha'  : 20:28Appearanceof  shafaq al-abya d  : 20:20SQM/AltitudeofSun vsTime-30-25-20-15-10-50510152025    1   9  :      1   0   1   9  :   1  4   1   9  :   2   2   1   9  :   2   6   1   9  :   3   0   1   9  :   3  4   1   9  :   3   8   1   9  :  4  4   1   9  :  4   8   1   9  :   5   2   1   9  :   5   8   2   0  :   0   2   2   0  :   0   6   2   0  :   1   0   2   0  :   1  4   2   0  :   1   8   2   0  :   2   2   2   0  :   2   6   2   0  :   3   2   2   0  :   3   6   2   0  :  4   0   2   0  :  4   6   2   0  :   5   0   2   0  :   5  4   2   0  :   5   8 Time    S   Q   M    /   A    l   t   i   t   u   d   e   o    f   S   u   n SQMAltitudeofSun Official timeof  Maghrib : 19:25Official timeof  cIsha'  : 20:34PlateauSQM: 20:26Disappearanceof  shafaq al-abya d  : 20:311st Phase2nd Phase3rd Phase BINOCULAR   THERMO-HYGRO METER FINDERSCOPE TRIPOD COMPASS BAROMETER CAMERA DETECTOR: EYE DETECTOR: SQM FIGURE 1. Spectral Response of SQM FIGURE 2 . Isha ’ at Kuala Lipis, 29 December 2007 FIGURE 3 . Isha ’ at Port Klang, 5 April 2008 Abstract. In this investigation, we focused on optical sky brightness at dusk from May 2007 through April 2008 intermittently. The measurements of twilight sky brightness were covered at two (2) different sites covering East and West coast of Peninsular Malaysia. The measurements were done using Sky Quality Meter. Results showed that there are clear indications of changes of the receipt of light when Sun at certain degree below horizon that visible by plateau form in twilight sky brightness dependences versus solar zenith angle. It is clarified that the yearly averages of solar depression by observation are best correlated within the range of 17.3 o  –  19.5 o  for Isha ’ . Keywords: Twilight , Prayer Time, Islamic, Scientific, Malaysia   N.N.M. Shariff, A. Muhammad, M.Z. Zainuddin, Z.S. Hamidi, Z.A. Ibrahim 7th MPSGC
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