for Muslims, Jews, and others…
A glance at this table of Muslim prayer times shows a number of different conventions and traditions.
First of all, I assume the angles represent the altitude of the centre of the apparent solar disc/ellipse below the horizon? Questions are, based on what reasoning did they come up with those values, how did different schools get different answers, and why are the angles sometimes symmetrical and sometimes not?
The OP opened this thread to Jews as well, and calculating Jewish prayer times is one of my hobbies, so I’m qualified to answer some of this.
That site references the calculations of the US Naval Observatory, and the USNO’s calculations tell you, mathematically, where the actual center of the sun is, relative to the horizon. Two critical things here:
[ol]
[li]“Actual” - NOT the apparent location, so you have to account for refraction through the atmosphere (which varies by the weather) and your own altitude (which varies by which part of town you’re in), so these calculations are NEVER going to be exact to the second, and the best you can hope for is a minute or two.[/li][li]“Center” - the calculations are for the center of the sun, and I see on that website that they define sunset and sunrise the same as the Jews: Sunset is when the last bit of the sun is no longer visible, and sunrise is when the first bit is first visible. In both cases, the center of the sun is below the horizon.[/li][/ol]
How did they come up with these values? Well, sunset and sunrise are pretty objective, and centuries of scientific examination and calculation went into it, pretty much like other natural phenomena. Darkness and dawn are much more subjective. How can one tell when there’s really no light in the sky coming from the sun? There are various opinions among the Jewish scholars about this, and I’m not surprised to see various views on that website among the Muslims too. Even the US Naval Observatory offers three different definitions of “twilight”: “Civil twilight” is when the center of the sun is less than 6 degrees below the horizon, “Nautical twilight” is less than 12 degrees, and “Astronomical twilight” less than 18 degrees.
Usually, the first “stars” that will be visible after sunset will be planets. Do they count for the definition of “dark”?
Judaism defined dark as when three stars are visible. This definition was then refined to specify three medium-size stars. I presume that the planets were on the large side.
Agreed that sunrise, sunset, and mid-day/midnight are straightforward enough.
One definition (without any particular tradition in mind) of astronomical twilight versus dark is that (theoretically, ignoring light pollution) at night the sun no longer illuminates the sky, and the faintest stars are visible. “Nautical” twilight seems to have to do with being able to distinguish the horizon?
Anyway, definitions such as these, along with being able to distinguish three medium-magnitude stars, need to be translated into geometric interpretation in order to be able to predict anything, and also for the reason that it might be cloudy, or the worshiper might live in a city, etc., and it be impossible or irrelevant to observe the actual stars or horizon. Furthermore, as you point out, these criteria are a bit subjective and fuzzy.
So they have to come up with something. It is not surprising that different authorities come up with different answers, but I am intrigued if someone knows some of the trivia behind it. For instance, considering the link I first posted, there is not too much difference between 18 degrees and 18.5 degrees (maybe at the latter angle you can be extra sure it is “really” dark), but then how come the Islamic Society of North America came up with 15 degrees? (Seems like they want to be sure the sky is not completely dark during the call to prayer.) And, most of all, why do half the traditions specify different angles for dawn and for dusk? (And how come
Umm al-Qura changed their calculation in 2008?) As for the time three stars appear in the sky, obviously that will be some time between civil twilight and nautical twilight, but I am interested in the chain of reasoning from that definition to coming up with a specific angle (and presumably there is a very old tradition as well as a modern scientific way including atmospheric modelling)
The intricacies here are all about tradition and interpretation. The astronomical calculations themselves are completely straightforward by today’s standards, especially since a precision of one minute is all that is required.
I know of one major Jewish authority who wrote that, based on his own observation in the New York area, “50 minutes after sunset, it is as dark overhead as in the middle of the night, and that’s sufficient. And the fact that there is still a little bit of light on the western horizon is irrelevant.” I can easily imagine other authorities who feel that one must wait until this degree of darkness is on the western horizon as well.
Regarding the different angles for dawn (Fajr) and dusk (Isha) that too is a good question. In Judaism too, the morning twilight lasts longer than the evening twilight. The simple reason is because different definitions are used - dawn is when the first light appears, and dark is when the stars appear. But that doesn’t really answer it. I have always wondered why we (Jews) don’t use the same yardstick at both ends; either when the light appears and disappears, or when the stars disappear and reappear. But thanks to this thread, I think I might have figured out a reasonable explanation: To define something based on a negative (we can’t see the stars anymore, we can’t see the light anymore) is a bit awkward. For those who are trying to make a legal (or religious or philosophical) system practicable, positive definitions work better: Dawn is when we can see the light, dark is when we can see the stars.
But that’s just my guesswork, and it only works for Judaism anyway. According to the OP’s website, Fajr is “When the sky begins to lighten (dawn)”, and Isha is “The time at which darkness falls and there is no scattered light in the sky”, and I’m stumped why those twilights would be of different durations.
I see that the different Muslim authorities are categorized with different geographical regions.
The human effect of dawn and dusk are different in different latitudes. At the equator, the sun rises and sets straight down in the East/West. At the poles, the sun creeps along the horizon as it rises and sets. At the poles, a sun at 15 degrees might have a long way to go over a long time before it’s finally gone.
There are special rulings for faithful above the arctic circle for example, otherwise you have a big potential problem during Ramadan or Yom Kippur, not to mention daily prayers. Obviously they are not going to go by the altitude angle if the sun never sets or there is no twilight.
I’m still trying to decode how they are calculating the normal prayer times (there must be some authoritative text for each version). Your different geographical regions theory is plausible, similar to what Keeve relates about New York City, maybe the North American Islamic Society decided 15 degrees is dark enough in modern North America. Wikipedia suggests some of this comes down to deciding how dark is dark, but also sketches differences among schools, e.g. one Sunni school says that the night prayer begins when complete darkness falls, while another says it’s when the red thread has disappeared from the sky. Maybe this already accounts for some of the asymmetry with the dawn prayer (by some authorities) called when the sun is lower than the night prayer, i.e., at dawn the time starts at first light, while for the dusk prayer it suffices just to wait until nightfall (and the Shia communities are obviously taking it earlier than the Sunni schools).
It does seem pretty complicated. Many Muslims I know use an app, which has a “ring tone” of the guy calling everyone to prey. I believe it uses GPS to show the correct direction. It makes me wonder how they knew what to do before smart phones.
Magnetic compass, and an indication on the wall of the prayer room. Outside of cities, people had and still have a much better idea of where east and west are (were the sun rises and sets). And, like Christianity and other religions, a very social activity: there only has to be one guy who knows…
I made a similar comment to a friend decades ago, when my only help was a Casio calculator.
He answered me: “It’s difficult to you because your brain thinks in terms of standard time, so you have to translate sunrise into hours and minutes, and then you translate sunset into hours and minutes, and then you have to do fancy arithmetic to calculate the various points in the middle. Back in the day when our only timepiece was a sundial, this was a LOT easier.”
If they are in a city near a mosque, there is a guy at the mosque in a minaret with big loudspeakers announcing the times.