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Jurnal Penelitian Fisika dan Aplikasinya (JPFA)Volume xx, Issue xx, xxxxxxxx 2020p-ISSN: 2087-9946e-ISSN: 2477-1775DOI: earch ArticleDetermining Accurate Fajr Time with Data SelectionAdi Damanhuri 1,a*, Akhmad Mukarram 1,b1Departement of Islamic Astronomy, Faculty of Sharia and Law, Universitas Islam Negeri Sunan Ampel,Surabaya, Jl. A. Yani 118, Surabaya 60231, Indoneisae-mail: a [email protected], b [email protected]insby.ac.id* Corresponding AuthorAbstractThe presence of the dawn light is indicated by the elevation angle of the sun, besides that the beginningof the dawn light also corresponds to the beginning of the subuh prayer time, so the elevation angle ofthe Sun is used as the standard for early subuh prayer time. In Indonesia, the standard is -20 but it isconsidered too early and because it is considered that the light of dawn has not yet appeared. By usingthe Sky Quality Meter (SQM), a photometric tool to quantify changes in sky brightness, the sun'selevation angle is obtained when dawn light is present, marked by changes in brightness in the form ofturning points. The night level affects the turning point because it gives a pseudo night effect, tominimize this effect the data used must have a night level of at least 20mpsas. To determine theinflection point, exponential function modeling is used and data normalization is carried out. Of the1,068 data originating from Agam, Garut, Kupang, Pasuruan, Pontianak, and Sumedang, the data wereselected with the condition that they had a night level of at least 20 mpsas or at grade 4 on the Bortlescale, resulting in 218 ideal data indicating the presence of dawn is when the angle Sun elevation at 17.07 .Keywords: dawn light; fajr time; sky quality meter.PACS: not more than 5 PACS codes, separated by semicolon (;) 2019 Jurnal Penelitian Fisika dan Aplikasinya (JPFA). This work is licensed under CC BY-NC 4.0Article History: Received: xxxxxRevised (Round 1): xxxxxAccepted: xxxxxDecided to resubmit (Round 1): xxxxxAproved with minor revision: xxxxxPublished: xxxxxHow to cite: Jatmiko B, et al. The Manuscript Template of Jurnal Penelitian Fisika dan Aplikasinya (JPFA).Jurnal Penelitian Fisika dan Aplikasinya (JPFA). 2020; 10(1): 1-6. DOI: https://doi.org/10.26740/jpfa.I. INTRODUCTIONThe beginning of the presence of thedawn light on the western horizon in additionto marking the end of the night, it is also forMuslims as a sign of the entry of the subuhprayer time. When the Sun is below the1

Jurnal Penelitian Fisika dan Aplikasinya (JPFA), 2020; 10(1): 1-6horizon with a certain height, sunlightinteracts with the upper atmosphere so thatthe Earth's surface will appear slightlyreddish [1] . In practice, the presence of dawnis represented by the elevation angle of theSun or the position of the Sun below thehorizon. The sun's elevation angle below thehorizon, which indicates the presence ofdawn, also indicates the beginning of subuhprayer time. In Indonesia, the elevation angleof the Sun used for the beginning of subuhprayer time is -20 or zenith 110 [2] , latelythis standard has been questioned because itis assumed that when the Sun is in thatposition, the dawn light on the westernhorizon has not yet appear. Dawn lightresearch has been carried out with variousapproaches, some using the naked eye,[3] ,using a digital camera [4,5] , and some usingsimple photometric tools, namely SkyQuality Meter (SQM) [2,6–8] .SQM is a simple photometric tool thatcan quantify the quality of sky darkness inunits of magnitude per arc second suare(mpsas) [9–12] . Research of the beginning ofsubuh prayer time using SQM was carriedout by looking for turning points from SQMdata which indicate the presence of dawn dueto changes in sky conditions from dark tobright due to the presence of dawn light.Then the obtained brightness level alsoindicates the level of light pollution, thehigher the brightness in the mpsas, the lowerthe level of light pollution [13–15] . Lightpollution has an impact on the emergence ofdawn light in the form of pseudo-night whichis caused by the absorption between sunlightand pollutant particles in the atmosphere, toovercome this, it is necessary to selectobservational data from the night which has anight level of at least 20 mpsas whichcorresponds to grade 4 on the Bortle [16,17] scale or Bright category [18] .There are several techniques used todetermine inflection points, including usingpolynomial functions as has been done bySaksono et al. [8] , with this method, thedetermination of the inflection point uses adegree of polynomial that varies frompolynomial of degree 3, polynomial ofdegree 4, polynomial degree 5, to polynomialdegree 6, depending on the SQM data itself,even several times have to reduceunnecessary data. In addition, in the researchconducted by Saksono, et al. used less idealdata because the data used came from alocation have sky quality below 20mpsas orfall into category 5 and above on the bortlescale [16,17] .In this study, determining the inflectionpoint of SQM data uses the solver method,which is a method that uses the exponentialfunction but to determine the variables usedas parameters for its function using the solvermenu [19–21] , besides the data used fordetermination the elevation angle of the Sunthat indicates the presence of dawn light isonly data that has been selected with thecondition that it comes from data that has aminimum night level of 20mpsas or category4 on the bortle scale in order to reduce theeffects of air pollution that can interfere withSQM signal capture. By considering lightpollution which can cause interference duringobservation [15] ,16 the data selected with themain criteria must come from data that has anight level of at least 20 mpsas or class 4 onthe bortle scale [16,17] or bright class [22] .The article sent to JPFA comes fromthe original research article (the articleoriginality or state of the art should bementioned in the introduction part) or thereview article about physics and itsapplication (see the scopes in JPFA)II. MATERIAL AND METHODSky Quality MeterSky Qualty Meter (SQM) is a simpleand very easy to use photometric tool formeasuring sky brightness levels. SQM isFirst and Second Author (if more than two, it should be written “et al”)2

Jurnal Penelitian Fisika dan Aplikasinya (JPFA), 2020; 10(1): 1-6produced by Unihedron, and has been widelyused for sky quality mapping research[23,24] , determine astronomical site [25,26] ,light pollution research [25,27–29] , researchin the health sector [28] , behavioral researchbirds [30,31] , to research on determining thetime prayer [2,8,13,15] . SQM uses a lightfrequency sensor TSL237, SQM in this studyis set to quantify in mpsas every 1 minutewith the direction of the sensor to the zenith[32] . Observations were made throughout theday in 2019. The data generated from SQMis in the form of ANSI data which containsinformation on sky brightness levels, timeand date data in Universal Time (UT) as wellas local time, solar elevation angle data,temperature data and count data. Skybrightness level is expressed in magnitudeper square arcsecond (mpsas), where SQMhas a precision level of 0.1 mpsas [33] .Which will be used for this study only dataon sky brightness, time and date data, as wellas data on the elevation angle of the Sun.Table 1.Location and Data SelectionSQM data is taken from theobservation data from 6 LAPAN ObservationStations, namely in Agam, Garut, Kupang,Pasuruan, Pontianak and Sumedang. All datathat can be analyzed are 1,068 data. Eventhough observations are made throughout theyear, not all data can be processed for severalreasons, including: because of interference atcritical moments such as from the moonlight,the data is disturbed due to the presence ofclouds, to disturbances due to rain. As shownin Table 1, the data to be used in determiningthe early dawn of time must fulfill therequirements, namely that the night level is atleast 20 mpsas. The night level is obtained byaveraging the Mpsas from 00.00 AM untilthe height of the Sun reaches -20 (z 110 ).To determine the dawn time in this studyonly selected data were used.Location of observationalLatitudeLongitudeNumberof DataAgam, West Sumatera-0.204430100.320057118Garut, West Java-7.650062107.69221465Kupang, East Nusa Tenggar-10.142009123.731231224Pasuruan, East Java-7.567506112.673702239Pontianak, West Borneo-0.007800109.365000221Sumedang, West Java-6.913079107.837213201LocationMethod of AnalysisTo determine the inflection point on thegraph, two data are used, namely the solarelevation angle data and the mpsas value,then the mpsas data is approached with theexponential function obtained using formula(1) of normal distribution [34,35] . Tosimplify the calculation, the solver menu isused, so that the prediction function gets anoptimal minimum difference from theoriginal data.𝑓(𝑥) 𝐶 𝑁 First and Second Author (if more than two, it should be written “et al”)1𝜎 2𝜋𝑥 𝜇 2𝑒 ( 2𝜎)3

Jurnal Penelitian Fisika dan Aplikasinya (JPFA), 2020; 10(1): 1-6(1)Where C is a constant level, N isnormalized, µ is mean, and σ is the standarddeviation. The values for C, N, µ, and σ willbe obtained using the menu solver,respectively, with the variables C, N, µ, andσ being used as boundary variables, or chisquare being selected as the objectivevariable.20 Meanwhile, to determine theinflection point, it is obtained from theFormula (2):shows that there is a relationship between thesolution obtained and the night level whichshows the quality of the sky when taking datawith the correlation coefficient (R2) .42.This shows that if we observe the presence ofdawn in a location that has a high night level,the solution will be deeper.𝑆𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝜇 3𝜎(2)The result of the calculation usingturning point formula is an inflection pointand is the final result that shows the elevationangle of the Sun at dawn. For example, foranalysis on January 10, 2019 for thePontianak location, the model is obtained asshown in the figure 1.Figure 2. The result before the data is selectedAs for the distribution of data based oneach observation location, namely: k, and (f)Sumedang, as shown inFigure 3 with the x-axis is the night level,and the y-axis of the inflection point solution(Sun Elevation Angle) show on figure 3.Figure 1. Plot of solver analysisIII. RESULTS AND DISCUSSIONFrom 1,068 the data shows that thesolution of the turning point on average whenthe elevation angle of the sun is 14.86 2.29 , with the deepest sun elevationangle obtained is -21.71 and the maximumis -8.95 . In addition, based on figure 2, itFigure 3. The result from every location before thedata is selectedAfter the data is selected with the maincriteria, the data must have a minimum nightlevel of 20mpsas, from 1068 data to 218 data,First and Second Author (if more than two, it should be written “et al”)4

Jurnal Penelitian Fisika dan Aplikasinya (JPFA), 2020; 10(1): 1-6which shows the average turning point at theelevation angle of the Sun -17.07 1.23º. Inaddition, the relationship between the nightlevel and the inflection point solution has asmall correlation coefficient, which is 0.02 asshown in Figure 4. With the deepest turningpoint solution is -21.71 and the highest is 12.64 , with the distribution as shown inFigure 5.Figure 5. The distribution of final resultFigure 4. The final result with data selectionIV. CONCLUSIONFrom the data above, it can beconcluded that the elevation angle of the Sunduring the presence of the dawn light ishighly dependent on the night level value.The higher the night level, the deeper theelevation angle will be. From the data with aminimum night level of 20 mpsas or grade 4on the Bortle scale, the mean elevation angleof the Sun in the presence of dawn light is 17.07 . Further research is needed byselecting a location that has a minimum nightlevel of 20 mpsas with a minimum durationof 1 year.ACKNOWLEDGMENT (OPTIONAL)Thanks to the National Aviation andSpace Agency of Republic Indonesia orLembaga Penerbangan dan AntariksaNasional (LAPAN) for providing skyobservation data with SQM to the public.And 2021 Research funding from UIN SunanAmpel Surabaya with cluster InterdiscplinerReserach.REFERENCES[1][2][3]Kaler JB. The Ever-Changing Sky: AGuide to the Celestial Sphere. 1st ed.Cambridge: Cambridge University Press;2002.Maskufa M, Munazat DR, Damanhuri Aand Abd. Shomad A. The Implication ofSky Quality Meter Technology inObserving the Dawn To Determine SubhPrayer Time, in: Proc. 2nd Int. Conf.Quran Hadith Stud. Inf. Technol. MediaConjunction with 1st Int. Conf. Islam. Sci.Technol. ICONQUHAS \& ICONIST,Bandung, Oct. 2-4, 2018, Indones., EAI;2020.DOI:10.4108/eai.2-102018.2295598.Hassan AH, Issa IA, Mousa M and AbdelHadi YA. Naked Eye Determination of theDawn for Sinai and Assiut of Egypt.NRIAG Journal of Astronomy andFirst and Second Author (if more than two, it should be written “et al”)5

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Kupang, East Nusa Tenggar -10.142009 123.731231 224 Pasuruan, East Java -7.567506 112.673702 239 Pontianak, West Borneo -0.007800 109.365000 221 Sumedang, West Java -6.913079 107.837213 201