Pitch Black Meter Determining the accurate time of Isha and Syuruk

Transcription

1 Pitch Black Meter Determining the accurate time of Isha and Syuruk Mohd.Zambri Zainuddin, Zety Sharizat Hamidi, Nazhatulshima Ahmad and Adzmir Abdul Latib. Department of Physics, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia. Abstact. The results of the accurate time of Isha and Syuruk are presented. Here, we apply a new technique by using Pitch Black Meter (PBM), an optical device that facilitate the measurement of sky brightness. This multipurpose device is a new approach where data were collected and it provides accurate measurement of sky brightness by reading the current value off the multimeter. The current is generated due to the changes of light intensity of the sky background. Data collected from the experiment will be analyzed and compared with theory. Abstrak.- Hasil keputusan bagi ketepatan masa waktu Isyak dan Syuruk dibentangkan. Di sini, kami mengaplikasikan teknik terkini dengan menggunakan Pitch Black Meter (PBM), peranti optik yang dapat mengukur kecerahan langit. Alat serbaguna ini merupakan rekaan terkini yang dapat mengumpul data dan ia memberikan pengukuran kecerahan langit yang tepat dengan ukuran dalam unit arus. Arus yang terjana bergantung kepada perubahan intensiti cahaya langit. Data yang telah dikumpul dari eksperimen akan dianalisa dan dibandingkan dengan teori. 1. Introduction Sky quality is one of the most persistent topics of discussion among astronomers. Most astronomers use limiting stellar magnitude as an indicator of sky quality. A device that can resolve those issues are most likely being welcome in this field.the Pitch Black Meter (PBM) is designed to make measurements by comparing the brightness of a light source with a given area of the night sky. Although it can be determined by calculation method, this device is a new approach where data collected and it provides accurate measurement of the sky brightness by reading the current value of the multimeter. The principle is by adjusting the the light intensity of the LED until it matches with the light intensity of the sky background. These techniques may provide new venues for using optical device in astronomy applications. This paper describes a components that consists in constructed the PBM. We also compare the results from the observations with theoritical data which had

2 been calculated in Moon Calculator (MoonCalc) program. We present the theoritical details in Section 2 and in Section 3, we discuss in how to build the PBM. The observations are described in Section 4 and results is given in Section 5. Finally, general discussion and main conclusion are presented in Section Theoritical Details In modern times, astronomical twilight (18 degrees) has come to be widely used for the determination of Isha times. As the average intensity curve of evening twilight indicates, the flux decreases to a minimum level, and thus it would seem appropriate that even for Islamic purposes, this should indicate a reasonable starting value for the end of 'Astro-lslamic Twilight' (AIT). Indeed, 18 degrees depression was a commonly used value for Isha in the medieval period, when it must have been based on careful observations. The aim of this paper is to define the starting point of evening (Isha) by observing the sky brightness using Pitch Black Meter (PBM). According to Fiqh rules, Isha times are determined when total darkness ends or starts, respectively. For automatic calculations, we determine the Isha times by calculating the time when the sun is at a certain distance below the horizon. For this purpose we use the twilight angle, which is simply the angle in degrees of the sun below the horizon. Some places use a fixed time after sunset (Maghrib) as the start of Isha time. Therefore, the zenith distance at evening (Isyak) can be calculated. The equation of zenith distance at evening (Isyak) is given by Z I = = 108 Thus, the Sun angle at the evening time (Isyak time), t I = cos cos 1 Z 1 t 1 is: sinδ1 sin cosδ cosφ where φ is the latitude of a location and δ is the declination of the Sun when conjunction time. 1 φ Finally the evening time can be determine as Evening time (Isyak)= Conjunction time + t 1 Implementing the same procedure and method we can also determine the begining of a day. Syuruk times are determined when dawn ends. The zenith distance of the sun is equal with zenith distance when the sun is set which is Therefore,

3 Z TT = 90 50" the Sun angle at morning time t TT is: t TT cos Z sinδ sinφ = cos 1 TT TT cosδtt cosφ Finally, we can calculate the Syuruk time which is Syuruk time= Conjunction time- t TT After several measurement of the sky brightness have been gathered in a particular period, a graph of current versus local time can be plotted. From the logarithmatic graph, we can predict the Isha and Syuruk time when the values becomes constant. The sun altitude versus local time graph provide the information on how the sun decline and rise on the horizon line. By combining both graph in a same axis, we can see the characteristics of any sky that been observed as well as finding the precise time of Isha and Syuruk if the sky is clear. 3. Building the Pitch Black Meter (PBM) In order to build the Pitch Black Meter (PBM), we have gathered all the main electronic components for the power supply contol box. The base for the circuit itself was createdby aeching process. Initially, a piece od Polyvinylchloride (PVC) plumbing tubing is the material that we used for the sighting tube. The appropriate diameter and length of the tube was varied on each prototype. Then the second prototype with several modification on the green filter holder, the placement of the LED plus an adapter to join between the sighting tube and tripod have been made. The schematic diagram of the variable power supply are shown in Fig. 1. A 90 telescope star diagonal is basically to make ease when viewing in addition for greater comfort whe making measurement of the sky. An adapter made from brass also been made to join the star diagonal into sighting tube. This connection must be made in order to prevent the diagonal star fallout from sighting tube.

4 Figure1 shows the schematic diagram of the variable power supply Basically the PBM consists of three components which are; a sighting tube, a variable power supply and an ordinary digital multimeter. The main parts of the sightingtube including a length of tubing, a green light emtting diode (LED) and a green glass filter. This LED is centered in the sky end of the tube. Fig.2 and Fig 3. show the pictures of power supply control box and the sighting tube with the green filter. Fig.2 Power Supply control box Fig.3 sighting tube with green filter

5 4. Observations Due to the repeatable measurements, it is important that our both eyes are adapted to the dark. For calibration purpose we obtained the measurements with the sky end of the tube closed. This observations can be started soon after the sun sets to determine Isha and early in the morning (Syuruk). The seeing are generally good although we noticed that the optical sky background depends on a number of parameter including moon angular separation, lunar phase, ecliptic latitude, zenith angle and phase of the solar cycle. Generally, the distance after the sun set are about 17 to 18 from the horizon. Theoritacally, the application of PBM is simple, by looking into the PBM, one sees the dark silhoutte of the LED against the green glass filter illuminated by the sky. Practically, the brightness of the LED is adjusted until it matches that of the sky. Here we present and discuss a several data that been taken at Teluk Kemang, Negeri Sembilan. The sky brigtness were observed in July 2003 until January Results The results obtained for each star are presented in this section. Figure 4 shows the current value (μa) versus local time. This data has been taken at Teluk Kemang, Negeri Sembilan on 29 th of July Results of the next day can been seen in Figure 5. We also present the analysis of the data that has been taken on 28th and 29th of August 2003 in Figure 6 and Figure 7. Figure 8 shows the analysis data of Syuruk (31 of July 2003) at Tanjung Bidara, Melaka. Finally, the results in determine Syuruk time at Kusza, Terengganu (13 of October 2003) was presented in Figure 9. All the observations were in a good sky condition, even though there is some cloud movement that might influence the results.

6 GRAPH 1 Graph DMM value ( ua ) versus ( minute ) 3 20: :45 19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 20:45 20:50 20:55 21:00-3 FIG. 4 shows the current value (μa) versus local time at Teluk Kemang, Negeri Sembilan (29 of July 2003) GRAPH 2 Graph DMM value ( ua ) versus ( minute ) :45 19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 20:45 20:50 20:55 21:00 20: FIG. 5. Characteristics of Isha time at Teluk Kemang, Negeri Sembilan on 30th of July GRAPH 3 Graph DMM value ( ua ) versus ( minute ) :45 19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 20:45 20:50 20:55 21:00 20: FIG. 6. Characteristics of Isha time at Teluk Kemang, Negeri Sembilan on 28th of August 2003.

7 GRAPH 4 Graph DMM value ( ua ) versus :45 19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 20:45 20:50 20:55 21:00 20: FIG. 7. Characteristics of Isha time at Teluk Kemang, Negeri Sembilan on 29th of August GRAPH 6 Graph DMM value ( ua ) versus :10 6:15 6:20 6:25 6:30 6:35 6:40 6:45 6:50 6:55 7:00 7:05 7:10 7:15 7:20 7:25 07: FIG. 8. Characteristics of Syuruk time at Tanjung Bidara Melaka on 31st of July GRA PH 7 Graph DMM value ( ua ) versus : :10 6:15 6:20 6:25 6:30 6:35 6:40 6:45 6:50 6:55 7:00 7:05 7:10 7:15 7:20 7: FIG. 9. Characteristics of Syuruk time at Kusza, Terengganu on 13th of October 2003.

8 6.Discussions In this section we discuss in details for each results. As can be seen from graph 1, we can locate the evening time by reffering this graph, which the value become constant. Starting 20.35, it is the Isha time. The Sun s altitude is , which is means that the Sun is 17 below horizon. A linear graph with negative gradient depict Sun distance averting from horizon. This experiment approves the calculation that have been made for Isha time. In the second results, the current value become constant at according to calculation time, the Isha time is At 20.36, Sun s altitude is below the horizon which is based on the MoonC60 Sotfware. Figure 3 shows that the Sun s altitude is below horizon at (Local time). The current value become constant until Data in figure 4 also approve the theory value. Here, the Isha time is at 20.25, with the Sun s altitude is below horizon. As shown in figure 5, the graph has become an exponential graph and the elevation of Sun is now liear with positive gradient. However, the Sun distance is getting near to horizon until Sun pass and rise above horizon. The altitude of the Sun at Syuruk time is We also can determine the Syuruk time is at 7.11 which is same with theory value. In figure 6, the Syuruk time is 2 minute difference with calculation. From the graph, the morning (Syuruk) is at 7.06 while in the calculation value is In principle, effective results can be obtained if there is no changes of the sky brightness on any particular area which caused by atmosphere condition, haze and light pollution. We also have to be alert in recorded the data at a precise time. 7. Conclusion The results of this investigation show that this optical device can give us a precice time in determine Isha and Syuruk time.however, the result of the data can be improve if we the experiment take places where there is no light source interruption. This circuit also can be improved by replacing the LED with more sensitive light detector.furthermore it has a good potential to be commercialize in astronomical field. References [1] Roger G. Barry and Richard J. Charley, Atmosphere Weather and Climate, Routledge Publishing ( 1992 ).

9 [2] Asgoir Brekke,Physics of the Upper Polar Atmosphere, John Wiley and Sons (1997), pg 1-27 [3] Sky and Telescope Magazine, A Simple Dark Sky Meter, Vol 101, No: 2 (February), pg [4] Sky and Telescope Magazine, Introducing the Bortle Dark Sky Scale, Vol 101, No: 2 (February), pg [5] Sky and Telescope Magazine, Application of Pitch Black Meter, Vol 101, No: 2 (February), pg 140