Middle-East Journal of Scientific Research 21 (9): 1641-16, 2014 ISSN 1990-9233 © IDOSI Publications, 2014 DOI: 10.5829/idosi.mejsr.2014.21.09.21740 Corresponding Author: Ahmed Kamil Ahmed, School of Physics, Universiti Sains Malaysia, 11800 USM Pulau Pinang, Malaysia. 1 Young Moon Visibility Criterion Based on Crescent Illumination and Sky Brightness Contrast Model Ahmed Kamil Ahmed and Abdul Halim Abdul Aziz 1 2 School of Physics, Universiti Sains Malaysia, 11800 USM Pulau Pinang, Malaysia 1 Department of Astronomy and Space, College of Science, University of Baghdad, Baghdad, Iraq 2 Abstract: The aim of this research is to present a new criterion for earliest crescent visibility based on the brightness difference between the young crescent and its background sky at sunset. In this work, 141 and 52 of lunar crescent observations from Malaysia and Iran respectively has been studied and analyzed. The data collected consisted of visible and non-visible observation data (naked eye and optically aided). The results indicated that the Moon’s percentage illumination (or Moon’s phase) must be 0.52 % ± 0.10 % and 0.39 % ± 0.10 % for Malaysia and Iran respectively. The average sky brightness during sunset measured was 6.80 ± 1.13 magnitude/arcsecond . 2 Key words: Moon Visibility Crescent Illumination Sky Brightness INTRODUCTION always is at the start with the lunar month. In addition, After conjunction, the first lunar crescent visible to one evening to the next [3]. The physiological variations the eye is called Hilal. The crescent sighting is used to of the observers’ eyesight also contribute to variability of determine the beginning of new Islamic month [1]. the results. However, it is a requirement that the crescent There are two approaches to determine the first visibility must eventually reach the human eye, whether aided or of lunar crescent, empirical and theoretical. The empirical unaided. approach is based on the selected observed parameters The contrast in the context of the first lunar crescent such as the Moon’s age, altitude or elongation, etc. to visibility is defined as the ratio of two components, the create a visibility criterion. The theoretical approach relies luminance of the lunar crescent and the brightness of the on known physics to derive mathematical visibility models sky [4]. In particular, the first astrophysical model that [2]. studied the earliest visibility of new lunar crescent was The problem here is to predict, from astronomical due to Bruin [5], in which the crescent brightness and that conditions, whether a new Moon can be sighted at a the twilight sky has taken into consideration [6]. The given location. Much effort has been put by the contrast between the Moon’s brightness and the astronomers to match predictions with observations. background sky is determined and compared to the Contrary to common belief, young crescent visibility minimum brightness that the naked human eye (or the has been difficult to predict accurately despite great telescope) can see. This results in a prediction model for strides being made in positional astronomy and related sighting the young crescent on any specific night from sciences. We hope this work will provide some insights any specific location [7]. into this issue and offer a scientific solution to a religious The most complete model has been proposed by issue. Schaefer [8] as well as Doggett and Schaefer [9]. This Atmospheric factors such as turbulence in the air, model calculates the quantity of (Rs) according to the humidity, dust and pollution also contribute to visibility formula: Rs = log [Rcalc/Rmin(vis)], which represent the of the new Moon. This is especially true when the logarithmic ratio between the actual brightness of the crescent is low across the sky, near the horizon, as it Moon to the required brightness of the Moon for these effects vary from one position to another and from