UniversitiTeknologi MARA Kelantan
National Academic Conference (ENRICH 2011)
AN INVESTIGATION OF ISHA’ PRAYER TIME: DETECTORS COMPARISON BETWEEN HUMAN EYES AND ELECTRONIC DEVICE FROM ISLAMIC AND SCIENTIFIC CONSIDERATIONS Nur Nafhatun Md Shariff1*, Amran Muhammad1, Zety Sharizat Hamidi1,2 1 University of Malaya, Malaysia 2 UniversitiTeknologi MARA, Shah Alam, Selangor, Malaysia *
[email protected] ABSTRACT In this paper, the determination of Islamic prayer time using scientific method has been extensively investigated. 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. Based on Islamic law code’s requirement, the measurements were done using human eye and electronic device (Sky Quality Meter) as the detectors which is Sunnah (qualitative) and scientific (quantitative) approaches respectively. Results showed that there are clear indications of changes of the receipt of light when Sun at certain degree below horizon that manifest itself by plateau form in twilight sky brightness dependences versus solar zenith angle. Interestingly, statistical analysis is also showed 1-2 minutes of differences compare with theoretical calculation of each data. It is also clarified that the yearly averages of solar depression by observation are best correlated within the range of 17.3o – 19.5o for Isha’. Keywords: Twilight; Prayer time; Islamic; Scientific; Malaysia 1. INTRODUCTION Early studies done by astronomers such as IbnMucādh, al-Bīrūnī, al-Qāyinī, IbnYūnus etc. (King, 2004, 2005). Ibn al- hā ir adopted various value for each prayer times such as 17 o for cIshā’ due to their asymmetry property (Goldstein, 1985). 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 (Chiplonkar & Kulkarni, 1959; Tyson & Gal, 1993; Ugolnikov, Postylyakov, & Maslov, 2004). While for this research, the author reconsiders from two pertinent reflections i.e. Islamic and scientific considerations which the later is “Islamic” in the deepest sense of the word. In the present paper, we show that elusive light can be detected i.e. shafaq al-a ya (Shariff, 2008). In that case, 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. In this paper, we investigated Isha’ prayer time. The overview of the experiment is as Fig. 1 below: Eye (logarithmic) Light Proton
Stimulus
Photodetectors
Dusk (Isha’)
Moment
Qualitative data
= Sunnah approach
interpret as SQM (linear)
Light to Frequency
Instruments
Detectors
Quantitative data
=
Scientific approach
Results
Figure 1: Overview of experiment
From the figure above, we understand that the stimulus is in form of light where it is detected during twilight by using two instruments i.e. human eyes (logarithmic) and Sky Quality Meter (SQM) in linear. As for human eyes the detector is photodetectors and as for SQM is light to frequency detector. Human eyes were used to collect qualitative data and SQM for quantitative data for the results. Where we understand human eyes representing sunnah approach. Whilst, SQM representing scientific approach. Nowadays, prayer times are also regulated by tables and also computed for each day by modern methods either in almanacs or prepared by Islamic authoritative department as requested. Still there are some
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National Academic Conference (ENRICH 2011)
discussions on which twilight angle should be used. General cIshā’ computations below has no opposition except the values of Z which is the value of the twilight angle that become one of the most speculating dilemma around the Islamic world. Officially JAKIM accepts 18 o for cIshā’. In addition, ICOP (International Crescent Observation Project) serves as virtual concourse of Muslim from all around the world to agitate those emerging issues concerning prayer times such as adīth on redness compared to whiteness of s y for c Ishā’. 1.1 General Computations of Twilight The criteria values play a vital role for computing the prayer times. As prayer times are based on location, it is required to know the Local Standard Time. Whilst the Sun at noon i.e. the centre of the Sun passes the Local Celestial Meridian, the Local Hour Angle (LHA) equal 0h or 24h. The connection between LHA and Greenwich Hour Angle (GHA) is as shown below: GHA = LHA - λL
(1.1)
The correlation linking GHA and Local Standard Time (LST) is: LST =
GHA GHA @ h1 X 24h GHA @ h 2 GHA @ h1 (1.2)
Where, GHA @ h1 = Greenwich hour time 0h on calculated date And, GHA @ h2 = Greenwich hour time 0h + 24h Then we obtain ∆δ by estimating the time for cIshā’ which is around 8 pm as follow: ∆δ
=
Estimation time X (δ 24 δ 0 ) 24
(1.3)
Next, we define Z as the twilight angle for cIshā’. After that, hour angle is calculated using this equation:t= Therefore cIshā’ time = LST + t
cos 1 [
cos Z A sin δ A sinφ L ] cosδ A cosφ L
(1.4)
(1.5)
In closing, the twilight angle is important and so do its value. Variable values give different result to prayer times for different location. 1.2 Instrumentation Performance Human eyes: According to Hecht, Schlaer and Pirenne Experiment (Cornsweet, 1970) that a subject is more sensitive to dim flashes of light if he has been in the dark for a period of time than if he has just come in out of the light. Dark adaptation is a common experience to be almost blind when first entering a movie theater but to be able to see quite a lot after 5 or 10 minutes (Davson, 1962). A Threads Experiment was conducted to verify the correlation between the human eye and SQM. From the experiment, the human eye can distinguish white and black threads when SQM readings are 20 to 22 magnitudes per arc second for ambient light. SQM: In order to understand the measurements, it was tested and characterized by checking the acceptance angle, linearity and spectral responsivity (Cinzano, 2005) by running photoelectric effects experiments (Shariff, 2008). As illustrated in Graph 1.1, shows the value of y (SQM) declines quite considerably and then rises steeply with wavelength. 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 1.2. The obtained response curve of our SQM multiplying the spectral responsivity of the TAOS TSL237 photodiode by the transmittance of the Hoya CM-500 filter, both provided by manufacturers – see Graph 1.2 which have a high correlation with human eye spectral response graph (Graph 1.3).
UniversitiTeknologi MARA Kelantan
National Academic Conference (ENRICH 2011)
SQM vs Wavelength 15
14
SQM (mag/arcsec^2) ± 0.1
13
12
11
10
9
8 SQM-without filter 7
SQM-with filter
6 300-UV
420-Violet
470-Blue
530-Green
620-Orange
700-Red
Wavelength (nm) ± 5
Graph 1.1: Graph of SQM versus wavelength
Graph 1.2: Spectral response of SQM
Graph 1.3: Spectral response of human eye
2. 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 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. preobservation, observation and post-observation (Shariff, 2008). The measurements were done at 400-700 nm in accordance of human eyes and SQM range. Data were taken in two minutes interval. Since the human eye is a stand-alone instrument, there is no need of supporting equipment. Yet the most essential is prior to commencing observing the elusive phenomenon, the eye must be in rest condition. It is important for the observer to avoid looking at bright light due to dark adaptation. The field of view of normal human eyes is 140o, even with this limitation the eye work very best, interalia instrument. Another item of concern to the observer is the type of cloud formation at the time of data taking. Besides observer should acclimatize with Bortle Dark Sky Scale, as it quantifies the observability of astronomical object and the interference caused by light pollution and sky glow. As for the SQM, the observer must press a button in order to activate the detector and then wait for a few second to obtain a reading. The data will be transferred to computer for further analysis. Since the input is in the form of numerical data, the author used Microsoft Excel software to transform these data into a spreadsheet after taking into account all the errors (Ghosh, 2007; Meeus) For qualitative data, on the other hand the author performed critical evaluation for the sceneries. For standard values of various quantities such as altitude of the Sun, the author used software called TheSky version 5.
UniversitiTeknologi MARA Kelantan
National Academic Conference (ENRICH 2011)
Figure 2.1: Flow chart of procedure
3. RESULTS AND DISCUSSIONS Qualitative: The beginning of cIshā’ is most indicated by the disappearance of shafaq al-a ya rather than shafaq al-a mar. Quantitative: Both criteria fluctuate between ranges 17.3o – 19.5o for cIshā’. The percentage of the accuracy for the quantitative and qualitative analysis was 0.5%.
Prayer time c
Ishā’
Table 3.1: Range comparison twilight angle (± 0.10) Average Qualitative Average Quantitative
Theory o
17.3 -19.2
o
Time Difference hafaq al-a mar – shafaq
o
o
18.25
17.4 -19.5
o
o
o
18.45
17.4 -19.2
o
Table 3.2: Time difference Maximum (± 0.10) Minimum (± 0.10) o
o
Average
Magnitude
18.3o
20.23-22.02
Average (± 0.10)
Minute ( )
Sun’s Alt.
Minute ( )
Sun’s Alt.
Minute (o)
Sun’s Alt.
15 (3.75)
18.707
2 (0.5)
17.646
8.5 (2.2)
18.177
al-a ya
For cIshā’, 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 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 some rate. The gradual acclivity demonstrates receipt of light when the Sun is at certain degrees below horizon (6o and 12o). 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 cIshā’ is indicated by a formed plateau – see Graph 3.1 – 3.2.
UniversitiTeknologi MARA Kelantan
National Academic Conference (ENRICH 2011)
SQM
SQM/Altitude of Sun vs Time
Altitude of Sun
25
20
15 Plateau SQM: 20:28 Appearance of shafaq al-abyaḍ: 20:20
5
:3 8
:3 4
20
:3 0
20
:2 6
20
:1 8
:1 4
:1 0
:0 6
:2 2
20
20
20
20
20
:5 8
:5 4
:5 0
:0 2
20
20
19
19
:4 6
19
:3 2
:3 8
19
19
:2 0
:1 4
:2 4
19
19
19
-5
19
:1 0
0 19
SQM/Altitude of Sun
10
Official time of cIsha' : 20:28
-10
-15 Official time of Maghrib : 19:13
-20
-25 Time
Graph 3.1: cIshā’ at Kuala Lipis, 29 December 2007
SQM/Altitude of Sun vs Time
SQM
Altitude of Sun
25 1st Phase 20 15 Plateau SQM: 20:26
10 2nd Phase
3rd Phase
SQM/Altitude of Sun 19 :1 0 19 :1 4 19 :2 2 19 :2 6 19 :3 0 19 :3 4 19 :3 8 19 :4 4 19 :4 8 19 :5 2 19 :5 8 20 :0 2 20 :0 6 20 :1 0 20 :1 4 20 :1 8 20 :2 2 20 :2 6 20 :3 2 20 :3 6 20 :4 0 20 :4 6 20 :5 0 20 :5 4 20 :5 8
5 0
-5
-10 Official time of cIsha' : 20:34
-15 -20 -25
Official time of Maghrib : 19:25
Disappearance of shafaq al-abyaḍ: 20:31
-30 Time
Graph 3.2: cIshā’ at Port Klang, 5 April 2008
4. CONCLUSION The goal is to advance qualitative and quantitative understanding of sky brightness at twilight for the optical range of wavelengths and twilight stages from daylight till nighttime. It was found out that there are strong relationships between astronomy, history of science and human perception in Islamic religious observances – is the principal in each situation. To answer the question of this title, it depends on the necessary whether for daily use or to revise current criteria. From the evidence, SQM is able to assist the process of determining the beginning of cIshā’ and yet human eye still give its best performance without SQM. Furthermore, there is no substitute for human eye since SQM just give numerical result (which has to analyse) rather than human eye which give almost immediate result. This makes SQM more precise rather than human eye. At this point, we can conclude that human eye and SQM correct each other and both approaches proved to be good for determining prayer times. We proposed, it is plausible that the value of twilight angle is fluctuate between for cIshā’ according what is given by the instruments.
UniversitiTeknologi MARA Kelantan
National Academic Conference (ENRICH 2011)
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