The accuracy of online-based prayer times applications

There are various types of prayer times that Muslims refer to on a daily basis. Specifically, there are offline and online prayer times as well as traditional and modern prayer times. Online prayer times that can be accessed from a mobile phone in forms such as android-based applications, online websites, and Google applications. The purpose of this study is to investigate the accuracy of onlinebased prayer times applications and seek for the possible consistency across these applications. This study employs a qualitative approach and a descriptive data analysis. The data collection is conducted through observations, literature study, and in-depth interviews. This study indicates different degree of deviations among online-based prayer times applications, in which Google applications show the most deviation among the others. This study suggests that Muslims refer to online applications recommended by the Ministry of Religious Affairs of Indonesia.


Introduction
Various types of prayer times emerge, and these can be found in both offline and online forms. Consequently, it is becoming easier for Muslims to find references regarding prayer times. Online-based prayer times applications are among popular time references used by Muslims throughout the world. These include android-based applications, website-based applications, and Google applications. However, the accuracy and validity of such online applications are often questionable since they somehow show different prayer times. Affairs. When compared, it is apparent that there are disparities of prayer times in these two online applications. Detailed comparison is presented in the table below.

Table 1. Comparison of two online-based prayer times applications
The accuracy of online-based prayer times applications (Encep Abdul Rojak, et. Disparities are apparent in the five prayer times in these two online applications. For example, a two-minute gap occurs during Fajr prayer and Asr prayer. Meanwhile, there are three-minute and four-minute gaps between Isha and Dhuhr prayers, respectively. The biggest time difference is found in Maghrib prayer with an eight-minute gap between these online applications. In addition to these time differences, all prayer times in the Google application clearly precede the times stated in the Ministry of Religious Affairs' online application. Previous studies about prayer times were conducted with different focuses of discussions. A study entitled "The Implementation of the Middle Coordinate of Regencies and Cities for Measuring Prayer Times" was carried out to explore the exact geographical coordinates that could be used as the basis for determining prayer times throughout a particular region. This study was necessary to develop a unitary prayer times system that could be implemented in regencies or cities that had large areas. This study resulted in two main findings. First, the implementation of the middle coordinate as the basis of measurement covered not only an area where the middle coordinate was located. Further, similar prayer times were also apparent in areas in which their coordinates deviated 0,5 degrees from the middle coordinate either to the west or to the east. Thus, the middle coordinate was preferably used as it likely covered large areas that belonged to certain region. Second, in term of geographical range, the use of the middle coordinate was sufficient to cover a region regarding the unitary prayer times system. As such, adding extra minutes (ikhtiyat) to an area that was not located exactly on the middle coordinate was unnecessary (Ardliansyah, 2017).
Another study entitled "Using Altitude Correction Data to Determine Prayer Times in Bandung City" was conducted by Rojak, Hayatudin and Yunus (2017). Through a qualitative approach, this study found that to determine the beginning of Maghrib prayer in Bandung City, data which consisted of altitude correction ought to be incorporated when measuring prayer times. These data were largely overlooked by prayer astronomers, which resulted in a substantial inaccuracy. This study recommended that altitude correction data were taken into account, especially for areas in Bandung City which were located 50 meters above the sea level (Rojak, Hayatudin and Yunus, 2017).
Principally, prayer times are based on the sun's positions towards the earth. Consequently, prayer times are measured locally according to geographical data in which an area is located.
Different geographical locations thus cause different prayer times throughout the Earth. A geographical positioning system (hereafter GPS) installed in a smartphone can help locate geographical data of a given area accurately. For instance, Ma'almusalli is a smartphonebased application that uses GPS data to determine prayer times in certain locations. A study which explores the accuracy of Ma'almusalli even when it is used in an offline state entitled "Offline Prayer Times System" was carried out by (Hafez, A., & Zeki, 2016).
Departing from this background, there is a lack of study which specifically investigates the accuracy of online-based prayer times applications. Given the importance of these applications for Muslims, this study is aimed at scrutinizing the accuracy of these applications and providing input for the development of the applications.

Methodology
This study employed a qualitative approach to investigate the data regarding online-based prayer times applications. Data collection was conducted through observation, literature review, and in-depth interviews. That is, the data from different applications were gathered and then compared one another. Additionally, seminal literature on astronomy was closely scrutinized while interviews with astronomers were also carried out. Collected data were further analyzed through a descriptive analysis method.

The basis of prayer times in the Islamic scriptures
Statements which discuss prayer times are written in the Quran and the Hadith. These statements describe five mandatory prayer times that each Muslim must perform. The Quran Surah an-Nisa verse 103 states: Verily, for all believers, prayer is indeed a sacred duty linked to particular times [of day]." In addition, it is stated in the Quran Surah al-Isra verse 78 that: Establish regular prayers at the sun's decline till the darkness of the night and the morning prayer and reading: for the prayer and reading in the morning carry their testimony." In addition to these Quranic verses, the Prophet Muhammad, peace be upon him, has provided more detailed prayer times in his Hadith. As narrated by (An-Naisaburi, 2010), the Prophet Muhammad stated: 1. Dhuhr prayer starts when the sun passes the meridian and is located slightly to the west.
It ends when the shadow of an object, at an angle of 90 degrees to the ground, is the same length as its height. However, according to the Hanafi's school of thought, Dhuhr prayer ends when the length of the shadow is twice the height of its object.
2. Asr prayer begins when the shadow of an object, at an angle of 90 degrees to the ground, is the same length as its height. While according to the Hanafi's school of thought, it begins when the length of the shadow is twice the height of its object. Asr prayer finishes before the sun's color turns into yellow. In an emergency situation, Asr prayer finishes before the sun sets or, in a different opinion, when the sun exactly sets.
3. The beginning of Maghrib prayer is when the sun sets. In other words, the sun's circumference cannot be seen in the west horizon. It ends when the twilight, a red reflection of the sun light on the earth's atmosphere, disappears. 5. Fajr prayer begins when the dawn appears and finishes when the sun rises. The dawn in here refers to the reflection of the sun light on the the earth's atmosphere that appears in the east horizon. This reflection largely permeates the horizon (Noor, Rosyadi and Hamdani, 2018).

The fiqh of astronomy in relation to prayer times
It is apparent that the sun is the object that becomes the basis for measuring prayer times. Based on the sun's coordinate positions towards the earth, digital prayer times are developed along with other elements (Yudhana, Fadlil and Rosad, 2019). The sun is a star that produces its own light through a chemical process that takes place in its core. In its core, fusion reactions occur in which four atoms of hydrogen fuse into a single atom of helium. With a strong pressure in the core and an enormous temperature of more than 15 million K, the fusion reactions continue to produce light (Gautama, 2010).
The position of the sun towards the earth impacts many aspects of life, in which one of them is the world time zone. As the position of the sun shifts towards the earth, the time in an area also shifts gradually. In other words, times are different from one area to another, depending on the sun's position towards certain areas (Rojak, 2021). As such, the sun's position also causes different areas to experience different prayer times. For example, prayer times in areas that are exposed to the sun will be different from the ones that are not exposed to the sun (Azhari, 2007). This different exposure occurs because, in addition to the movement of the earth rotating the sun, the earth is a sphere.

The position of the sun towards prayer times
In the Hadith, Prophet Muhammad indicated that prayer times were based on the position of the sun. Muslim astronomers define the position of the sun as the unit of measurement that represents the altitude of the sun or the distance of the sun from the zenith. The altitude of the sun is specifically calculated using the sun angle equation and is converted into units of times. In other words, the position of the sun in a certain altitude equals to a specific time in a given area (Ali, 1997). Through this calculation, prayer times in certain areas can be determined.
Primarily, there are two astronomical data that are used to determine prayer times, namely the altitude of the sun and the hour angle of the sun. Data from these two aspects should be calculated prior to determining prayer times (Niri et al., 2012).

a. The altitude of the sun (h)
The altitude of the sun in the sky can be calculated by measuring its distance from the horizon skirt towards the zenith and the nadir. The scale of measurement used in this calculation ranges from 0° to 90°. Other term used in calculating the altitude of an object in the sky is zenith distance. There are differences between the altitude of the sun and zenith distance when they are used to determine prayer times. To determine prayer times, the altitude of the sun is measured from its horizon on the ground level until it passes the vertical skirts, both the zenith and the nadir, of the horizon. Meanwhile, zenith distance measures the distance of the sun from the zenith.
A positive value (+) is given to indicate that the sun's altitude is above the horizon.
Meanwhile, a negative value (-) is used to show that sun's altitude is below the horizon.
The positive and the negative values mean differently when using the sun's altitude as the basis for measuring prayer times. The positive value indicates that the sun can be visually observed, while the negative value indicates that the sun in invisible (Khazin, 2005). Figure   2 illustrates the altitude of the sun in details.
Horizon +h T B Zenith Nadir -h α β Figure 2. The altitude of the sun measure from the horizon skirts. The positive value occurs when the sun's altitude is relative to the zenith. The negative value is given when the sun's altitude is relative to the nadir.
Based on the altitude of the sun, prayer times are determined. In other words, the altitude of the sun observed from certain areas determines which prayer times that take place in those areas (Mohamoud, 2007). Furthermore, different sun's altitudes will also determine different prayers that must be performed. For example, the time for Asr prayer is distinct from Maghrib prayer due to different sun's altitudes observed in the horizon. The data about the altitude of the sun is collected by the Ministry of Religious Affairs to determine prayer times in Indonesia. For instance, according to the Ministry of Religious Affairs, Dhuhr prayer starts when the altitude of the sun passes the zenith slightly to the west. Meanwhile, the beginning of prayers such as Maghrib, Isha, and Fajr is determined when the altitude of the sun is -1°, -18°, and -20° towards the nadir, respectively (Islam, 2010). Muslim astronomers, however, have dissenting opinions about these degrees (Ilyas, 1984).
Online and offline prayer times are both based on a similar measurement system, that is using the altitude of the sun as the basis of the measurement (Hafez, A., & Zeki, 2016).
The data about the sun's altitudes are carefully to make sure the accuracy of prayer times. This occurs because the time for Asr prayer emerges from the combination of two shadows, which are the shadow of the beginning of Dhuhr prayer and the shadow of a stick whose length is the same as the stick. In other words, the combination of these two shadows creates the value where the sun's altitude indicates the beginning of Asr prayer (Hadi, 2009). A more detailed description of how Asr prayer is determined can be seen in the figure 4 below. Asr prayer can be done mathematically without having to observe the sun directly. This equation can also be programmed into digital devices such as computers and calculators.
As such, researchers can use these devices conveniently when determining prayer times.

b. The hour angle of the sun (t)
In astronomy, the hour angle of the sun refers to the angular distance of the sun measured from the celestial poles to the position of the sun. In other words, it is an angle between celestial poles, the meridian plane, and the declination plane that passes the sun (Khazin, 2005). The hour angle of the sun is denoted as a small t, in which the value of the t is converted into global times system (Ray, 2012).
The hour angle of the sun ranges from 0° to 180°. The starting point of this angle lies on the zenith, that is when there is a certain distance between the sun and the zenith. To calculate the value of the hour angle of the sun, there are three aspects that must be incorporated into an equation. First is the latitude of an area. The second and the third aspects are respectively the declination of the sun and the altitude of the sun. The equation of this calculation is: Cos t = Sin h / Cos φ / Cos δ -Tan φ x Tan δ 2 (Khazin, 2007).

The accuracy of online-based prayer times
There are two types of online-based prayer times. The first is web browser-based prayer times and the other is application-based prayer times. Both types of prayer times are easily accessed by Muslims at their fingertips.

Web browser-based prayer times
Keywords inserted in a web browser substantially influence the results of a search. It is apparent that the search produce results that are based on a rating scheme. Consequently, the results are not always accurate. In the context of searching for prayer times, selecting the right keywords will influence the accuracy of prayer times.
The researchers in this study mitigated several keywords for searching prayer times via web browsers. These include: 1. "Jadwal Shalat" (prayer times) -when typing this keyword in the browser, the top results were a website managed by the Ministry of Religious Affairs and Jadwalshalat.org.
It has been mentioned previously that prayer times provided by the Google search engine were not accurate compared to prayer times issued by the Ministry of Religious Affairs.
Alternatively, it is important to use an appropriate keyword to search for authoritative websites that provide reliable prayer times. From our observation, we recommend the following keywords: jadwal shalat online, jadwal shalat update, and jadwal shalat aplikasi online.
These keywords direct us to authoritative online sources as mentioned above.

The calculation of prayer times on online systems
Online prayer times are developed according to certain data and algorithm that are programmed into online systems. The equations used to calculate the position of the sun towards the earth become the basis of the algorithm. While anyone can use these equations to create their own online prayer times, it is imperative that they coordinate with the authority such as the Ministry of Religious Affairs to make sure the accuracy of data regarding prayer times (interview with Mulyawan, 2020). For example, an online application by Google claims in its website that it uses data from the Ministry of Religious Affairs as the main reference.
However, it is found that the developers of this website never made an official request to the Ministry of Religious Affairs to use its data (interview with Fahmi, 2020).
Although this Google-based application claims that it refers to data from the Ministry of Religious Affairs, its prayer times are substantially different from the ones developed by the Ministry of Religious Affairs (see figure 6). A 3 to 7-minute difference is found in the two applications for all of the five prayer times. While the difference might be small, but this impacts Muslims' activities greatly. For example, the difference in the Maghrib prayer can cause confusion when Muslims are about to break their fast. Thus, it is important that online applications, such as the one developed by Google, coordinate with the authority to maintain the accuracy of prayer times (interview with Supriatna, 2020). Unlike the Google-based application, there is an online application which is developed based on a certain algorithm that gathers information of prayer times from multiple sources.
As seen in figure 7, this application provides not only prayer times from one source but also prayer times from multiple sources which represent religious officials around the world. In addition, this application also displays which criteria used when measuring the prayer times in a given area.
In general, criteria that are used to measure both offline and online prayer times are as follows: 1. Prayer times are determined by measuring the position of the sun towards the earth.
2. The yearly movement of the sun towards the earth can reach up to 23,5° as observed from the north to the south. b. Dhuhr prayer: the sun passes the meridian and is located slightly to the west.
c. Asr prayer: According to Maliki, Shafi'i, and Hambali's schools of thought, Asr prayer begins when the shadow of an object, at an angle of 90 degrees to the ground, is the same length or a little bit longer as its height. While according to the Hanafi's school of thought, it begins when the length of the shadow is twice the height of its object.
d. Maghrib prayer: the sun's circumference cannot be seen in the west horizon.
e. Isha prayer: it starts when the twilight disappears or when the position of the sun is at -18° from the horizon.
4. Data taken for measuring prayer times accurately are calculated through certain trigonometric equations.

Conclusion
Online-based prayer times applications are not all accurate. For example, Google application, which displays prayer times from other unofficial websites, shows inaccurate prayer times compared to other official applications. Online applications developed by local officials are consistent with the application developed by the Ministry of Religious Affairs in terms of the accuracy. To help find accurate prayer times on the internet, it is imperative to use certain keywords such as jadwal shalat online, jadwal shalat update, and jadwal shalat aplikasi online. These keywords direct us to authoritative online applications whose prayer times are similar one another. This in turn indicates the accuracy of prayer times issued by them.