Quetions About SalatTimes

Q1: I live in London and I found Fajr and Isha times provided by your program are not the same as the times given by our local Mosque in London. Why there is a difference and what are the correct times?

A1: The times of Fajr and Isha are effected by the chosen depression angles (Fajr, Imsak and Isha angles). Some Mosques are using the value of -18 degrees for all angles while SalatTimes has default of -16, -13.5 and -16 degrees respectively. If you look into old textbooks you will find out that the conditions for True Dawn are not fulfilled when using -18 degrees (i.e. it is too dark). I believe the times provided by SalatTimes are the correct times but still you can get the same times as your Mosque by changing the values of Fajr, Imsak and Isha angles to the same value as the one used by your local Mosque.

Q2: Can you tell me why the time printed in Pakistani newspapers for Imsak and Maghrib are different for Hanafi fiqh?

A2: For difference in Imsak time see A1. According to Imam Abu Hanifa (AS) Maghrib time is the time of sunset. Local newspapers (as well as most other local information sources) add few minutes to Maghrib time to compensate for distance, observer height and other meteorological conditions. For example in Bahrain they add 6 minutes to Maghrib time to cover the entire area of Bahrain. In SalatTimes all parameters are calculated precisely and no approximate times are used. If you set the configuration parameters in SalatTimes correctly then you do not need to add any extra minutes. The calculation engine in SalatTimes is much more reliable than the sources for most of local newspapers.

Q3: What is the difference between Zawal and Duhr times? Is Duhr time really the time of Duhr prayer or we have to add few minutes to obtain the time of Duhr prayer?

A3: Duhr time is the time when the sun passes local meridian completely. Noontime is the time of midday((Nisf-Annahar). The difference between the two times is at most 1.5 minutes. In Arabic, Zawal time indicates the time when the sun passes the middle of the day. Thus, Duhr and Zawal time should be the same. However, some people believe that Zawal time is the time when the sun starts passing the local meridian (i.e. at midday). Therefore, they give the time of Noon as Zawal time. This definition is not correct and should be avoided. In addition, as the case with other prayer times, certain people are adding few minutes to Duhr time to compensate for something (e.g. to not pray with the Sun worshippers). Anyhow, as I failed to find the source for such compensation in Hadith and Sunna, I do not recommend adding any extra minutes.

Q4: I like your program and wonder if it is possible to send me the source files or at least the formulae you have been using?

A4: SalatTimes is mainly based on two different theories, one for the Sun (and other planets) and one for the Moon. The constants used by these two are more than 1000 in double precision. Various additional sub-theories and formulae are used as well in the calculation engine. Such amount of theories and formula are not easy to present for public use. If you would like information about the main theory behind the program, VSOP87 then please check the links on http://geocities.datacellar.net/SiliconValley/Vista/9311. On the homepage of VSOP87 you will find (among other thing) Fortran code that shows how the data is to be used. For the moment, I have made a DLL publicly available and users can use it to build their own applications. The use of DLL is very simple and there is a test program included as well. The DLL is available for downloading from the homepage of SalatTimes. There is a plan to release a lib.a for Unix as well.

Q5: Your definition for Maghrib time according to Jafari Fiqh is not correct. Maghrib time is 10-20 minutes after sunset. Can you motivate your definition?

A5: The Jafari Fuqaha use 2 different definitions for Maghrib time. The majority of "now days" Fuqaha define the time of Maghrib as when eastern twilight disappears. The minority define it as the time of sunset. However, I failed to find the source for first definition in old Fiqh books. In fact I found a Hadith from Imam Jafar Assadiq (AS) in which he rejects delaying the time of Maghrib. The only thing I found was they use the disappearance of eastern twilight to make sure the sun is really below the horizon. In other words, when the eastern twilight vanishes then the sun is definitely below the horizon. Now days we can exactly find the place of the sun at any moment and we can determine for sure when it is below the horizon. So why using eastern twilight for that?!
Anyhow, as indicated in the on-line help file there are disagreements within the same school of law and Maghrib time is one such example. There is an option in the program to add few minutes to Maghrib time to obtain desired time. Also, you can read Fatwa (in Arabic) from Saed Fadlu-Allah in Lebanon regarding the subject and he is declaring the time of Maghrib, is the time of sunset. There is also a text (in English) from M. Jawad Maghnia with similar information.

Q6: I do not understand the words "NotValid, "AlwAbove" or "AlwBelow". What are these and what shall I do when I get one of these instead of prayer times?

A6: The words "NotValid" indicates precise time can not be calculated (due for ex. the altitude of the sun is reaching maximum or minimum or demanded accuracy can not be obtained). "AlwAbove" indicates the sun is always above the required altitude, while "AlwBelow" indicates the sun is always below the required altitude. You may get one of these if you calculate for place with high latitude (e.g. Stockholm). In such circumstances there are other rules to follow. SalatTimes has the rule "1/7 of day when needed" as default rule. This rule gives alternative times Imsak, Fajr and Isha times when these are not possible to calculate. The times provided by this rule are very close to standard times (just compare times given by this rule with times just before or after days with invalid times). However, this rule should not be used for places with latitude more 60 degrees. For such places it is recommended you set the rule to "Nearest location-all prayers". The majority of Fuqaha agree on this rule for places with high latitude. SalatTimes support many other rules and default configuration can be changed at any time using the "Configuration" option.

Q7: I do not have any knowledge in Astronomy or Mathematics and have no idea about the meaning of angles, distances, heights or others. I live in Bergen in Norway. Can you tell me what I have to do, to get correct prayer times using your program?

A7: First you need the co-ordinates for your place. Use the links (NIMA) available on the homepage of SalatTimes to find the co-ordinates for your place. NIMA tells you, your place has latitude 51°43'00"N and longitude 6°30'00"E . Next, is Bergen on the side of a mountain and you can have open view in the city to see the sunset? If yes then find out how many meters is the mountain over see level (you can find such information in local atlas). If you failed to find this information then just find rough approximation (i.e. 500 meters, 1000 meters and so). Finally, find out how many kilometers are you far from the center of Bergen (you do not need to be exact, just an estimation). Now start SalatTimes and press the "Location" button. Use the arrow keys (or mouse) to select Oslo in the list of locations. Change the name of city from Oslo to Bergen, type the latitude, longitude and height values and press "add" button to add the location to the database. Then press the button "SelectHome" and then "close" button. Next, press the "Configuration" button and change the distance to the value you got for your city, press "Ok" and that's it!
Now you can use the program to calculate prayer times for your location for any time. You do not need to do changes next time you start the program, only type the required date.

Q8: I would like to know what formula are you using for Qibla direction and why are you converting geographic latitude to geocentric? According to the paper written by Kamal Abdali no such conversion is needed.

A8: SalatTimes uses the following formula to calculate Qibla direction:
mod(atan2(sin(lonb-lona)*cos(latb),cos(lata)*sin(latb)- sin(lata)*cos(latb)*cos(lonb-lona)),2*pi)
The formula is mathematically equivalent with the one mentioned by Abdali and others. Both formulae are valid only on perfect sphere. If the Earth was a perfect sphere then geocentric latitude would be the same as geographic. However, since this is not the case there is a difference between the two. The difference is quiet small and has a maximum (11'32".73) when geographic latitude is +-45° 05' 46".36. Since the difference is small it is often not mentioned. However, if one needs to be precise, geographic latitude should be converted to geocentric.

Q9: I have a question about Moon data. Why you did not implement any sighting criterion when you already calculated all-important parameters?

A9: The visibility of the Moon is not definitive or conclusive (as the case with the instant of New Moon). There are several criteria available to predict the visibility of the Moon. However, the crescent of Ramadan, 1418H, was the definite answer that non-of them is reliable enough. Most of these criteria indicated the crescent will be visible only in certain parts of the Pacific (close to Hawaii islands) and in best case in certain parts of USA. But reports indicated the crescent was seen in places as far as Pakistan! I did not implement any sighting criterion because there is no reliable one yet.

Q10: I like your program but have problem to set the configuration data correctly. Specially, I do not know to what values I should set for Fajr, Imsak and Isha angles. You mention that default values are good enough to be used but I see that the provided times are much different from what the rest of my people is using. I live in United Arab Emirates. Please help?

A10: Most Muslim countries (including UAE) are using the value of -18 degrees for Fajr and Isha depression angles. Imsak time is defined to be few (5-10) minutes before Fajr time. The question I would ask is why they use -18? or even better I would ask, do we see the True Dawn when the sun reaches -18 in Muslim countries? I do not think so and anyone can easily proof this (i.e. there is no sign at all for the Fajr or True Dawn when the sun is at -18). However, I am not a Faqih and can not make a conclusion in such subject. To be on the safe side ask your Faqih about this. If the answer is follow the rest of the people then just change the default setting. I have already sent this question to many scholars but so far non-replied to me. When I receive any reply, I will include it in this Faq.

Q11: Your program does not calculate the Magnetic Declination accurately for long period of time like other programs do. Are there any plans for improvements?

A11: Anyone with knowledge in magnetic fields would realize that there is no way to calculate -accurately- the earth magnetic declination for long period of time! What you are reading in other programs is no more than an indiscreet way of marketing products and has nothing to do with science. In fact most programs do not mention what theories they use because they know when these are mentioned then their claim will be questioned. Here I mention the problems we had with Carmin (Producer of GPS receivers) as their old and new products gave different results because they use models for different time period.

Q12: I think I found a bug in your program. The Qibla direction from magnetic north is different from the value provided by our Qibla compass?!

A12: I am afraid the fault is in your Qibla compass rather than in SalatTimes! Many people do not realize that the position of earth magnetic pools is changing all the time. Qibla compasses produced several years back would give higher error margin when used during resent years. This is due the fact earth magnetic pools are not in the same place as they were when these compasses were produced. That's why many navigation instruments have to be continuously adjusted to the changes in the position of earth magnetic pools. Thus, I would encourage you to buy new compass and use it instead of your old Qibla compass.

Q13: I live in the USA and there are people who suggest to use the direction of rhumb line (the direction indicated by flat map) to identify the Qibla. Your program does not have such function and I wonder if there are plans to include it soon.

A13: In the USA, there has been a suggestion to use the direction indicated by flat map to identify the Qibla but this claim was discarded completely by mathematicians and astronomers. Anyone with basic knowledge in spherical mathematics can easily come to a conclusion about this suggestion. The following points highlight why this suggestion is faulty: 1. To determine the Qibla, the shortest path to Mecca should be considered. If the shortest path is not considered then Qibla can NOT be found unambiguously. 2. The shortest path between two points on the surface of a sphere is along the great circle joining them. This statement is easy to prove in spherical mathematics. 3. Rhumb line between two points on the surface of the earth is not always the shortest path. If Rhumb lines are always the shortest path then previous statement can not be true (i.e. consider a place with similar latitude as Mecca. Rhumb line will follow the parallel of latitude, which is not a great circle). Thus, using the direction of rhumb line to identify the Qibla is wrong and there are no plans to include such function.

Q14: I do not know how to use the shadow of the Sun to identify the Qibla. Can you help me with an explanation?

A14: Identifying the Qibla using the shadow of the Sun is an easy task. First, you have to do it during daytime. Second, you need to copy the diagram indicated by SalatTimes to a paper. Third, you need to go out in an open area with direct access to sunlight. Place the paper on flat surface and stick a pen in the center of the circle. You will see the shadow of the pen fall somewhere into the paper. Rotate the paper until the shadow of the pen fall on the line representing the shadow in the diagram. Qibla direction is then, the one indicated on the diagram.

Q15: I have access to a program that calculates rise and set times for the Sun. This program is just like yours claiming an accuracy of 1 second. However, results from this program do not agree with the results from SalatTimes and the error can reach up to 1 minute! Would you mind telling me which program is the correct one?

A15: Perhaps both!
Programs written for astronomical application does not follow the principles used in religious applications. Many astronomers used to define the sun set as when the center of the sun is touching the horizon. This definition is an accordance with set times for other planets and stars. In addition, they use fixed value for refraction, which is applicable for this exact position of the sun (i.e. when the center touches the horizon). In Islam, the Sun is set when it is completely below the horizon. This means, the upper limp of the sun is just passed below the horizon. This is the definition used in SalatTimes and perhaps this is the reason for difference.