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Limiting altitude separation in the new moon's first visibility criterion
Abstract
The minimum altitude separation between the moon and the setting sun for
new moon's earliest visibility is found to be close to 4°. This
result together with an earlier study on limiting elongation makes the
new Moon's earliest visibility criterion most complete and
comprehensive.
... However, Schaefer criticized McNally's claim and confirmed Danjon's limit [18]. Ilyas [19] agreed with Maunder's limit and modified it to 10.5 • for naked-eye visibility. Yallop [16] agreed with Ilyas' limit, although decreased it to 10 • . ...
... Fotheringham [10] 12 • Maunder [11] 11 • Ilyas [19] 10.5 • Yallop [16] 10 • Fatoohi [1] 7.5 • Danjon [12] and Schaefer [21] 7 • Odeh [17] 6.4 • McNally [13] 5.5 • ...
... Ilyas [22], on the other hand, reformed Bruin's criterion and found that the minimum limit of visible width of the moon was 0.25 ; (15 arcseconds). In [19], he developed a new criterion and claimed that the moon could not be visible if it had been found on the horizon when the depression of the sun was 4 • (DEP = 4 • ). He verified the Maunder and Bruin visibility criteria and extended their curves using extrapolation to cover visibility conditions in higher geographic latitudes. ...
Various theories have been proposed since in last century to predict the first sighting of a new crescent moon. None of them uses the concept of machine and deep learning to process, interpret and simulate patterns hidden in databases. Many of these theories use interpolation and extrapolation techniques to identify sighting regions through such data. In this study, a pattern recognizer artificial neural network was trained to distinguish between visibility regions. Essential parameters of crescent moon sighting were collected from moon sight datasets and used to build an intelligent system of pattern recognition to predict the crescent sight conditions. The proposed ANN learned the datasets with an accuracy of more than 72% in comparison to the actual observational results. ANN simulation gives a clear insight into three crescent moon visibility regions: invisible (I), probably visible (P), and certainly visible (V). The proposed ANN is suitable for building lunar calendars, so it was used to build a four-year calendar on the horizon of Baghdad. The built calendar was compared with the official Hijri calendar in Iraq.
... Kriteria lain di antaranya dikembangkan oleh Mohammad Ilyas dari IICP (International Islamic Calendar Programme), Malaysia. Kriteria visibilitas hilal yang dirumuskan IICP (dengan sedikit modifikasi: bukan nilai rata-rata yang diambil sebagai kriteria, tetapi nilai minimumnya) terbagi menjadi tiga jenis, tergantung aspek yang ditinjau (Ilyas 1988, Ilyas dan Khalid-Taib 1989, Djamaluddin 1995: a. Kriteria posisi bulan dan matahari: beda tinggi bulan-matahari minimum agar hilal dapat teramati adalah 4 o bila beda azimut bulan -matahari lebih dari 45 o , bila beda azimutnya 0 o perlu beda tinggi > 10,5 o . ...
... Untuk mengurangi efek kesalahan pengamatan tersebut, dilakukan analisis awal untuk memilah data berdasarkan kriteria berikut: a. Kriteria utama: Bila beda tinggi bulan-matahari kurang dari 4 o (kriteria beda tinggi minimum menurut Ilyas, 1988), harus didukung hasil pengamatan yang dilakukan oleh tim pengamat independen di tiga lokasi atau lebih. Selain itu, data pengamatan minimum harus didukung satu laporan lengkap tentang waktu pengamatannya sehingga bisa diuji kebenarannya berdasarkan perbandingan dengan waktu terbenam bulan. ...
... Bila seluruh data pengamatan (38 data) diplotkan (Gambar 3.1), maka terlihat bahwa jarak sudut bulan-matahari minimum 3,2 o , jauh di bawah limit Danjon yang menyatakan limit hilal dapat teramati bila jarak sudut bulan-matahari 7 o (Shaefer, 1991). Demikian juga dengan umur bulan minimum (4,3 jam) yang jauh lebih rendah dibandingkan dengan kriteria Ilyas, yaitu 16 jam (Ilyas 1988, Ilyas dan Khalid-Taib 1989, Djamaluddin 1995. Beda tinggi bulan-matahari minimum sekitar 1 o untuk beda azimut 5 o , sedangkan untuk beda azimut 0 o beda tinggi minimum sekitar 4 o . ...
Research on crescent visibility in Indonesia has not been conducted yet systematically based on astronomical analysis to obtain the criteria of possibility of crescent sighting. While, the criteria are needed in determining the beginning of Islamic calendar, especially for Ramadhan, Shawal, and Zulhijjah. This analysis is conducted to overcome such a problem, by using documentation of crescent sighting during 1962-1997 in Indonesia. The results can be concluded as follows: Crescent sighting with low altitude tends to be reported from less then 3 location, likely due to misjudging of foreground object (e.g. lamp) considered as crescent. Misjudging of the crescent due to misidentification of planet Venus or Mercury is proved for low altitude crescent sighting. After eliminating foreground and background objects, it is obtained the criteria of crescent visibility in Indonesia: (1). Moon age should be > 8 hours. (2). Moon-Sun angle should be > 5,6 deg. (3). Moon-Sun altitude difference should be > 3 deg (crescent's altitude > 2 deg) for Moon-Sun azimuth difference of approximately 6 deg, while for Moon-Sun azimuth difference 9 deg.
... The criteria are less than the known international criteria (e. g. Danjon limit which theoretically supported by Schaefer, 1991;Ilyas, 1988;Ilyas and Khalid-Taib, 1989). ...
... The object might be foreground one (such as lamp, airplane, or bright tiny cloud) or background one (such as planet Venus or Mercury). To minimize such confusion, the data was selected as follows: a. Main criteria: If Sun-Moon altitude difference less than 4 o (minimum altitude difference of Ilyas, 1988), the observations must be done by three ore more independent groups. Besides, at least one report should be a complete one, which can be compared with astronomical calculation. ...
... This indicates that point like objects with atmospheric scattering effect have confused the observers. There are some reports that passed the selection criteria, but considered to be too low compared to the international criteria such as Ilyas (1988). But, there is no scientific reason to reject the remaining reports, since all probable confusions have been removed in addition to the honesty of the observers who took the oath by the name of Allah. ...
So far, there is no single criterion of hilaal (the first Crescent) visibility adopted in Indonesia. In making calendar, it is used "wujudul hilaal" criteria, i. e. moonset later than sunset, even for one minute. The present hilaal visibility criteria is based on simple observational analysis, i. e. Moon altitude more than 2 o , Sun-Moon distance more than 3 o , and Moon age more than 8 hours. By documentation of hilaal sighting during 1962-1997 in Indonesia, systematical analysis was done. All reports have passed religious procedure, i. e. taking the oath in front of local religious court official. After removing reports of low altitude sighting from less then three independent location and that with probable Venus or Mercury confusion, it is obtained the revised criteria of hilaal visibility in Indonesia: (1). Moon age should be > 8 hours. (2). Sun-Moon angular distance should be > 5,6 o . (3). Sun-Moon altitude difference should be > 3 o (crescent's altitude > 2 o) for Sun-Moon azimuth separation of ~ 6 o , while for Sun-Moon azimuth separation < 6 o , it is needed more altitude difference. For Sun-Moon azimuth separation of about 0 o , the altitude difference should be > 9 o .
... If the above criterion is fulfilled, then the crescent will definitely be sightable from somewhere in the world on the critical day -although occasionally the only such 'favoured place' will be in the central Pacific Ocean. The chance of success is greatest at a location where the New Moon appears vertically above the Sun (Ilyas, 1988) -which could easily be well north or well south of the equator: it is determined by the season of the year and the lunar celestial latitude. ...
... The Sun-Moon "separation" is of course determined by their celestial latitudes as well as by their longitudes. It is also known as the Arc of Light (Ilyas, 1988, Schaefer, 1988, Odeh, 2006. It measures the apparent distance between the centres of the two discs from a geocentric perspective, such that topocentric diurnal parallax need not be considered. ...
Based on the moon-sun separation at dusk on the equator on the International Date Line, it ensures that the same Islamic dates will apply in every part of the world.
... eberapa kriteria-kriteria kenampakan anak bulan yang terkemuka dan menjadi rujukan utama di dalam pembinaan kriteria. Kriteria tersebut adalah daripada al-Qallas (King, 1987), al-Khawarizmi (Louay J. Fatoohi, 1998), Ibnu Yunus (King, 1988), Caldwell (Caldwell, 2011),Fotheringham (Fotheringham, 1910), Maunder (Maunder, 1911), Danjon (Danjon, 1936), Ilyas (M. Ilyas, 1988), McNally (McNally, 1983), Bruin (Bruin, 1977), Odeh (Odeh, 2004), ...
... dan tinggi bulan daripada ufuk(M.Ilyas, 1988), adalah jauh lebih tinggi daripada kriteria kenampakan anak bulan yang lain sepertiDanjon, Maunder, Fatoohi(Lovay J. Fatoohi, Stephenson, & Al-Dargazelli, 1998) dan ...
In the early stage of Islam, the Hijriah date is determined by new moon observation every 29 th day cycle of moon phase. However, the expansion of Islam to another civilization and its transition to the next age contribute to differentiating cultures and practices of determining the date of Hijriah that is unique from one to another. The instance for the differentiation of cultures and practices can be seen in diverse implementation of new moon visibility criteria in determining the date of Hijriah. The question is, how differentiation of practice in determining the date of Hijriah particularly the new moon visibility criterion exactly happens? To provide a clarification to this
... eberapa kriteria-kriteria kenampakan anak bulan yang terkemuka dan menjadi rujukan utama di dalam pembinaan kriteria. Kriteria tersebut adalah daripada al-Qallas (King, 1987), al-Khawarizmi (Louay J. Fatoohi, 1998), Ibnu Yunus (King, 1988), Caldwell (Caldwell, 2011),Fotheringham (Fotheringham, 1910), Maunder (Maunder, 1911), Danjon (Danjon, 1936), Ilyas (M. Ilyas, 1988), McNally (McNally, 1983), Bruin (Bruin, 1977), Odeh (Odeh, 2004), ...
... dan tinggi bulan daripada ufuk(M.Ilyas, 1988), adalah jauh lebih tinggi daripada kriteria kenampakan anak bulan yang lain sepertiDanjon, Maunder, Fatoohi(Lovay J. Fatoohi, Stephenson, & Al-Dargazelli, 1998) dan ...
... Umur Bulan sebesar 15 jam 29 menit di atas diperoleh dari kesaksian me-ngamati hilal di Ampenan Lombok tanpa adanya catatan perihal modus pengamatan yang dilakukan; apakah pengamatan dengan mata telanjang Beda tinggi minimum berdasarkan data empirik adalah 7,36 0 . Nilai ini lebih tinggi daripada yang diperoleh Ilyas (1988) yang diadopsi Djamaluddin (2011), yaitu sebesar 4 0 . Dari studi teoretik, Sopwan & Raharto (2012) memperoleh rentang beda tinggi Bulan dan Matahari untuk kasus hilal yang mudah diamati dengan mata telanjang sebesar 10 0 -11 0 , sedangkan untuk hilal yang hanya dapat diamati dengan bantuan alat optik 4,5 0 -5,5 0 (hilal dekat ekuinoks), 5 0 -6 0 (hilal dekat solstis), dan saat dekat aphelion dan perihelion sebesar 5,5 0 . ...
... Diperlukan data keberhasilan observasi hilal valid yang lebih banyak untuk dapat mengkonfirmasi nilai 3 0 ini. Nilai ARCV minimal 3 0 mendekati yang diperoleh Ilyas (1988), yaitu sebesar 4 0 , yang diadopsi Djamaluddin (2011) sebagai usulan kriteria hisab-rukyat Indonesia. ...
ABSTRAKPerbedaan dalam memulai dan mengakhiri ritual kolosal (puasa Ramadhan dan Idul Fitri ataupun Idul Adha) di kalangan umat Islam Indonesia masih berpotensi untuk terjadi pada masa depan selama belum disepakatinya suatu kriteria tunggal bagi visibilitas hilal yang memiliki landasan ilmiah kokoh. Dalam naskah ini diusulkan sebuah kriteria visibilitas hilal bagi wilayah Indonesia berdasarkan data kesaksian mengamati hilal yang dikompilasi oleh Kementerian Agama Republik Indonesia dan sumber lain yang telah dihimpun lembaga Rukyatul Hilal Indonesia. Kriteria yang diusulkan tidak semata berdasarkan konfigurasi geometri ketiga benda langit terkait (Matahari–Bumi–Bulan), namun turut mempertimbangkan faktor kecerahan langit senja dan langit malam. Agar dapat diamati, umur Bulan minimal pascakonjungsi dan elongasinya berturut-turut harus lebih besar dari 15 jam dan 80. Beda tinggi (ARCV) minimal sebesar 110 untuk beda azimut (DAZ) 00, dan berkurang dengan membesarnya beda azimut Bulan–Matahari. Selain itu berhasil diperoleh penjelasan teoretik atas kriteria ketinggian minimal hilal 20 yang selama ini dianut Kementerian Agama RI. Hasil yang diperoleh ini dapat menjadi pijakan sementara bagi sebuah kriteria visibilitas hilal di Indonesia yang valid secara keilmuan. Dengan terus bertambahnya data observasi dan semakin baiknya pemodelan matematis, penerimaan umat Islam terhadap suatu kriteria tunggal yang teruji akurat diharapkan dapat ABSTRACTWe proposed hilal visibility criteria for area near to equator. The criterion is not based on geometric configuration of the Sun–Earth–Moon only but considered the contribution of twilight and night sky brightness also. The data came from hilal observation reports compiled by Religion Ministry of Republic of Indonesia and Rukyatul Hilal Indonesia (Indonesia Hilal Observation) organization. In order to be observed, the age of the Moon after conjunction and its elongation should be greater than 15 hours and 80 respectively. The relative altitude (ARCV) is 110 for relative azimuth (DAZ) of 00, and decreases with larger relative azimuth. We also provide theoretical explanation for hilal minimum altitude criterion of 20 that have been adopted by the Ministry of Religious Affairs. Based on current available data, the proposed criteria can be used as the one of scientifically-based hilal visibility criterion. With the growing of hilal observation data comes from around Indonesia, we can improve and test the validity of the criteria based on model of Kastner. Then we can be optimistic about Muslims acceptance of unique criterion for hilal visibility in Indonesia.
... Efforts for obtaining an astronomical criterion for predicting the time of first lunar visibility go back to the Babylonian era (Sultan 2007). Major developments appear to have taken place at the hands of early Muslims (Ilyas 1988). The Muslim year contains twelve lunar month, each starting at sunset of the evening of the first sighting the lunar crescent. ...
... Many methods for predicting the visibility of the new lunar crescent have been proposed throughout history and new models are still being developed (Hoffman 2003). In the twentieth century Fotheringham (1910), Maunder (1911), Danjon (1936), Bruin (1977), Ilyas (1983bIlyas ( , 1988, Schaefer (1988), Yallop (1998), Caldwell and Laney (1999) and Odeh (2004) have developed empirical methods for predicting first sighting the new crescent moon. ...
About 70 years ago “André Danjon” a French astrophysicist showed that as elongation of the moon decreases the arc length of crescent gets less too. By studying the recent observational data, he concluded that at 7 degree elongation, the length of arc (cusp to cusp) will reach zero degree. Today, this value is named as Danjon limit, which points to the limit at which the moon crescent is formed. Danjon believed that the effective factor for occurring this limit was the shadows of moon’s mountains. Later researchers have obtained different values for this limit. In this research based on the new data, the decreasing dependence of length of arc versus elongation was obtained. The results show that the Danjon limit is about 5 degrees. The effective factors to form the Danjon limit are then given and discussed. By considering the effects of astronomical seeing and shadows of lunar features, the values of the arc length were calculated and compared with the observational data curve. The results of this study show good agreement with the observational data. The present research shows that the above-mentioned effects can reduce the length of arc. The effect of libration and roughness of the lunar terrain of the moon in forming the moon crescent were also considered, and the possibility of observing thinner crescents by photometric model and breaking the Danjon limit were given.
... 3 Kriteria MABIMS sendiri dalam perumusannya berdasarkan pada kompilasi hasil pengamatan hilal internasional, jadi didalam kriteria MABIMS belum ada faktor Meteorologi dan akuitas mata yang dijadikan sebagai bahan pertimbangan. Kriteria MABIMS yang baru menghasilkan kriteria tinggi hilal minimal 3 o , yang diambil dari penelitian Ilyas (1988), Caldwell- Laney (2001) dan elongasi bulan 6,4 o , diambil dari penelitian Odeh (2006). 4 Kriteria tersebut merupakan revisi dari kriteria visibilitas hilal yang lama, yang sudah dianggap tidak lagi relevan untuk dijadikan sebagai acuan kriteria visibilitas hilal. ...
... Dalam penyelidikan moden, pelbagai kriteria dibangunkan dan ia dapat diteliti dalam kajian Fotheringham 15 ,Maunder 16 ,Bruin 17 ,McNally 18 ,Schaefer 19 , Odeh 20 dan Mohammad Ilyas 21 . Berdasarkan kajian Mohd Saiful Anwar Mohd Nawawi,22 terdapat tiga bentuk kriteria yang biasanya digunakan dalam penentuan kenampakan anak bulan untuk awal bulan Hijrah untuk realiti semasa pada hari ini. ...
Setiap kaedah penentuan kenampakan anak bulan mempunyai fungsi tersendiri. Fungsi itu dapat dijelaskan berasaskan metodologi mengenal alam. Dalam penelitian ini, metodologi mengenal alam yang dikemukakan oleh Daud al-Fatani diaplikasikan untuk menjelaskan fungsi berkenaan. Pengumpulan data dalam kajian ini adalah berdasarkan metode dokumentasi, manakala analisis data adalah berasaskan metode analisis kandungan. Hasil kajian mendapati kaedah hisab adalah ẓannī yang lebih kuat berbanding kaedah rukyah tetapi ia lebih lemah berbanding kaedah istikmal. Sehubungan itu, fungsi kaedah hisab hanya sebagai pengesah dan penafi kepada laporan cerapan terutamanya apabila menentukan kenampakan anak bulan bagi bulan Ramadan, Syawal dan Zulhijjah.
Each method of determining the crescent's visibility has its own function. The function can be explained based on the methodology to know the universe. In this study, the methodology to know the universe as presented by Daud al-Fatani is applied to elucidate the function. Data collection in this study is based on the documentation method, while data analysis is according on content analysis method. The study found that the calculation method is conjecture (ẓannī) which is stronger than the observational method but it is weaker than the rounding method (istikmal). Accordingly , the calculation method can be function only as a verifier and a disclaimer to the observation report primarily when determining the crescent's visibility for the month of Ramadan, Syawal and Zulhijjah.
... In recent decades serious attempts have been made Crescent sighting activities are carried out on the 29 day towards globalising the Islamic calendar by scholars of the previous month. It is more involved than just like Ilyas [2]. Following his critical appraisal of the computing the times of conjunctions. ...
To date, there is no single global Islamic calendar for the community. Over the years, the computation
of the Islamic calendar has become a subject of much debate. In this paper, we propose a unified global
Islamic calendar (UGIC) based in the concept of “expected visibility”, International Dateline and a single
calendar for the whole world. We used a new sightability criterion to determine young crescent visibility that
is based on eye-detectable contrast between the crescent illumination and sky background. We propose an
unconventional reference for calendar construction that is based on a line instead of a point. We embraced
the International Date Line as day (and month) separator. A three-year calendar has been produced based on
the above method for evaluation.
... The same is done on the basis of both the ancient and the modern criteria. Ilyas [8][9][10] called this curve the International Lunar Date Line (ILDL), and defines it as the curve where the probability of sighting the new lunar crescent is 0.5. Ahmed [1] has prepared excellent software called MoonCal whose version 6 is available on the net. ...
Basic techniques of Computational Astronomy are reviewed and presented as the essential tools for simulation of Lunar phenomena. The importance of accurate determination of Julian Date and the Local Sidereal Time is discussed that are essential to determine the local time of sunset and the local coordinates of any object at that time. During the 20th century, a number of authors have contributed towards the understanding of the problem of earliest sighting of crescent Moon. The work of Maunder, Schoch, Bruin and Schaefer has been crucial in the development of this understanding. More recently, the work of Yallop, Ilyas, Ahmed and Shaukat has received great recognition. The work of Ahmed and Shaukat has been based mostly on the Yallop's Criterion. However almost all the modesl are based on the observational data of Schmidt who made observations from Athens for over 20 years during the late 19th century. In this work, a model of q-values developed by Yallop is analyzed in view of Maunders and the Indian Criteria along with the actual semi-diameter of the crescent Moon. The basic criterion is modified on the basis of data more recently collected.
... The graph is extended to higher latitude. Ilyas C (1988) This is an improved criterion of Ilyas A. The moon is visible if the chosen set of data lies above the curve. ...
The determination of the Islamic calendar is paramount in Islam because it strongly relates to worship, like Ramadan fasting, eid-al-fitr, and zakat fitr.
We show that in high geographic latitudes (approximately > 50º north or south), the lunar months of 28 and 31 days are possible.
For the central zone of the Earth (approximately 50ºN-50ºS), Islamic months have lengths of 29 and 30 days depending on the place of Earth from where we observe the first lunar crescent. We verify that all the lunar months have two durations for the central zone, one of 29 days and the other of 30 days. For higher latitudes (50º N or S to 61.5º N or S), we find that months can have 28 and 31 days lengths. We determine the length of the lunar months using the Month Change Line concept, applying the extended Maunder criterion.
Abstrak Pergantian hari konsep kalender Islam terjadi pada waktu maghrib dimasing-masing lokasi, hal tersebut bersifat lokal. Pergantian hari dalam konsep kalender Matahari terjadi pada waktu local 00:00 (tengah malam) yang dimulai dari 180o BT. Fase Bulan dihitung berdasarkan waktu dalam kalender Masehi. Perbedaan konsep pergantian hari tersebut menjadi dasar dalam pengelompokkan hilal menjadi hilal hari pertama dan hilal dari kedua. Hilal hari pertama adalah hilal yang terjadi pada tanggal yang sama dengan fase Bulan Baru. Hilal hari kedua adalah hilal yang terjadi satu hari setalah tanggal fase Bulan Baru. Hilal hari kedua meruapakan hilal hari pertama ditambah 1 hari kalender masehi. Penelitian ini mengelompokan dan memberikan gambaran karakteristik hilal hari pertama dan hilal hari kedua saat Matahari terbenam.
ABSTRACT The concept of the day in the Islamic calendar takes place at maghrib in each location. The changing day in the concept of the Solar calendar occurs at 00:00 local time (midnight) which starts at 180 o E. The Moon phase is calculated based on Solar calendar. The difference in the concept of the day becomes the basis for the grouping of the hilal to be the first day of hilal and the second days of hilal. the first day of Hilal is the hilal that occurs on the same date as the New Moon phase. The second days of Hilal is the hilal which occurs one day after the date of the New Moon phase. The second days of hilal is the first day of the new moon plus 1 calendar day. The characteristics of the hilal from the first and the hilal of the second day at sunset will be discussed in this paper.
Many astronomers have studied lunar crescent visibility throughout history. Its importance is unquestionable, especially in determining the local Islamic calendar and the dates of important Islamic events. Different criteria have been used to predict the possible visibility of the crescent moon during the sighting process. However, so far, the visibility models used are based on linear statistical theory, whereas the useful variables in this study are in the circular unit. Hence, in this paper, we propose new visibility tests using the circular regression model, which will split the data into three visibility categories; visible to the unaided eye, may need optical aid and not visible. We formulate the procedure to separate the categories using the residuals of the fitted circular regression model. We apply the model on 254 observations collected at Baitul Hilal Teluk Kemang Malaysia, starting from March 2000 to date. We show that the visibility test developed based on elongation of the moon (dependent variable) and altitude of the moon (independent variable) gives the smallest misclassification rate. From the statistical analysis, we propose the elongation of the moon 7.28°, altitude of the moon of 3.33° and arc of vision of 3.74 at sunset as the new crescent visibility criteria. The new criteria have a significant impact on improving the chance of observing the crescent moon and in producing a more accurate Islamic calendar in Malaysia. ABSTRAK Ramai ahli astronomi telah mengkaji kebolehnampakan bulan sabit sepanjang sejarah. Kepentingannya tidak dapat dipertikaikan, terutama dalam menentukan kalendar Islam tempatan dan tarikh peristiwa penting Islam. Kriteria yang berbeza telah digunakan untuk meramalkan kemungkinan kebolehnampakan bulan sabit semasa proses pencerapan. Walau bagaimanapun, setakat ini, model kebolehnampakan yang digunakan adalah berdasarkan teori statistik linear, sedangkan pemboleh ubah penting dalam kajian ini adalah dalam sukatan membulat. Oleh itu, dalam kertas ini, kami mencadangkan ujian kebolehnampakan baru menggunakan model regresi berkeliling, yang akan membahagikan data menjadi tiga kategori kebolehnampakan; dapat dilihat dengan mata kasar, mungkin memerlukan bantuan optik dan tidak kelihatan. Kami memformulasi prosedur tersebut untuk memisahkan kategori menggunakan sisa model regresi berkeliling yang sesuai. Kami mengaplikasikan model tersebut dalam 254 pemerhatian yang dikumpulkan di Baitul Hilal Teluk Kemang Malaysia, bermula dari Mac 2000 sehingga kini. Kami menunjukkan bahawa ujian kebolehnampakan dibangunkan berdasarkan pemanjangan bulan (pemboleh ubah bersandar) dan ketinggian bulan (pemboleh ubah bebas) memberikan kadar salah pengkelasan terkecil. Daripada analisis statistik, kami mencadangkan pemanjangan bulan pada 7.28°, ketinggian bulan 3.33° dan aras penglihatan 3.74° ketika matahari terbenam sebagai kriteria baharu kebolehnampakan bulan sabit. Kriteria baharu ini memberi kesan yang besar dalam meningkatkan peluang melihat bulan sabit dan menghasilkan kalendar Islam yang lebih tepat di Malaysia studied.
We propose a new Hilaal (lunar crescent formed immediately after conjunction) visibility criterion apply to tropical region utilizing modified mathematical model of near-sun objects visibility. By using only naked eye positive sightings of Hilaal , then we are calculating the Moon and Sun observation parameters to obtain the visibility function for each case. Moon – Sun altitude difference (ARCV – Arc of Vision) and elongation (ARCL – Arc of Light) at the first observable moment have been chosen as parameters and used in developing new visibility criterion. The data show that the minimum ARCV and ARCL value for naked eye observation at the moment of Hilaal is observed are 8.4° and 7.1°, respectively. Our results can be proposed as a scientifically criterion for constructing Hijri calendar for tropical region (including Indonesia) as an alternative to Jakarta Recommendations criterion.
ABSTRAK Penelitian ini memanfaatkan data kesaksian mengamati hilal yang telah dihimpun oleh Kementerian Agama Republik Indonesia (1962-2011) dan Rukyatul Hilal Indonesia (2007-2009) untuk memperoleh kriteria visibilitas hilal di Indonesia menggunakan model fungsi visibilitas Kastner (1976). Data mengalami proses seleksi mengikuti prosedur Djamaluddin (2000) dan hanya kesaksian yang memiliki nilai fungsi visibilitas positif yang dinilai valid untuk kemudian digunakan dalam analisis. Dengan merajah data berdasarkan umur Bulan dan elongasi, beda tinggi dan beda azimut, serta beda tinggi dan elongasi maka didapat kriteria berupa batasan-batasan minimum dari beberapa parameter fisis (umur Bulan, elongasi, beda tinggi Bulan-Matahari, dan beda azimut Bulan-Matahari). Hasil yang diperoleh memberikan nilai-nilai minimum yang lebih besar daripada kriteria yang dianut pemerintah selama ini, dan mendekati nilai-nilai yang diperoleh peneliti lainnya. Hasil ini dapat menjadi usulan kriteria tunggal yang memiliki landasan ilmiah yang kokoh. Kata Kunci: Fungsi Visibilitas Kastner-Kecerahan Langit Senja-Model Fungsi Visibilitas Kastner 1 PENDAHULUAN Di Indonesia telah ada beberapa usulan bagi kriteria visibilitas hilal. Pemerintah melalui Kementerian Agama menganut suatu kriteria visibilitas yang disebut Kriteria MABIMS, yang diadopsi dari pertemuan Menteri-Menteri Agama Brunei Darussalam, Indonesia, Malaysia, dan Singapura. Isi kriteria tersebut adalah ketinggian minimal hilal 2° dan elongasi minimal 3° atau usia sejak konjungsi minimal 8 jam. Pada dasarnya kriteria di atas tidak untuk memastikan bahwa hilal dapat diamati, melainkan untuk keperluan penyusunan kalender hijiyah (Widiana, 2000). Sebagai sebuah solusi sementara, Djamaludin (2011) mengusulkan kriteria visibilitas hilal yang kemudian disebut sebagai Kriteria LAPAN yang disempurnakan, yaitu dengan menyandingkan ketinggian sebagai fungsi beda azimut dengan elongasi. Dari sekian banyak kriteria visibilitas hilal yang sudah ada tidak ada kriteria yang berlaku universal untuk seluruh lintang pengamat (Hoffman, 2003). Konfigurasi geometri seperti yang dinyatakan berupa parameter dalam kriteria MABIMS memang berpengaruh terhadap visibilitas hilal, namun ada faktor lain yang juga sangat berpengaruh terhadap visibilitas hilal, yaitu faktor kecerahan langit terutama kecerahan langit senja. Kecerahan langit senja diyakini berhubungan dengan lintang geografis, ketinggian lokasi dari permukaan laut, musim, dan kandungan aerosol di atmosfer (Mikhail et. al, 1995). Dengan latar belakang di atas, penelitian ini dimaksudkan untuk memperoleh jawaban atas permasalahan berupa kriteria visibilitas hilal di Indonesia yang memiliki validitas ilmiah. Kriteria yang dimaksud dibangun berdasarkan data laporan pengamatan hilal positif dari seluruh wilayah Indonesia dengan turut menyertakan faktor serapan atmosfer dan kecerahan langit senja. 2 LANDASAN TEORI Fungsi visibilitas Kastner merupakan suatu model visibilitas pada saat senja untuk objek-objek langit (bintang, planet, dan komet) di dekat Matahari (Kastner, 1976). Model fungsi visibilitas Kastner menyertakan faktor ekstingsi optis atmosfer sebagai fungsi ketinggian, kecerahan objek di luar dan di dalam atmosfer Bumi, sudut depresi Matahari yang berkontribusi terhadap kecerahan langit senja, dan kontribusi kecerahan langit malam. Dalam perhitungan kecerahan hilal menurut pengamat di permukaan Bumi digunakan koefisien ekstingsi atmosfer k = 0,19 (menyatakan kondisi atmosfer bersih). Semakin besar nilai koefisien atmosfer, semakin kotor kondisi atmosfer (Allen, 1973). Fungsi visibilitas ∆m, dinyatakan sebagai: ∆ 2 5 m , log R, = (1) dengan c s a L R , L L = + (2) Dalam Persamaan 2, R didefinisikan sebagai kontras kecerahan (luminance), L c adalah kecerahan objek yang diamati di permukaan Bumi
The visibility of lunar crescent has been explained in Islamic Law (fiqh) by previous scholars. Until today, the explanations which were nuance in qualitative sense are still provide vacuum and need to be studied critically with different method particularly in quantitative approach. Therefore, this paper will present the application of scientific approach using sky illumination measurement to explain lunar crescent's visibility. The approach combines computational and observational technique will help fiqh in explaining the phenomenon explicitly and strengthen it with empirical descriptions. The sky illumination measurement was performed using a light meter in Teluk Kemang, Malaysia from 2007 until 2009. The authors employed the observational data to obtain the estimate values of sky illumination for the day which lunar crescent was seen from 1972 until 2009. The analyses of the values then were correlated with relative altitude and sun depression angle. The authors found that the range of sky illumination for lunar crescent to be seen is 2.95-92.80 lux. For the highest sky illumination value (92.80 lux), relative altitude should be. 5° and the depression angle should be. 0.5°.
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