notes on prayer time calculation

[Moustafa Elqabbany <elqabbany at yahoo dot com>]

Assalamu alaikum & Eid Mubarak to you all.

I've worked on and dealt with prayer calendars for
some time, and I'd like to document what I've
observed/learned to date in the hopes that it might
help out future efforts.  I currently don't have time
to code for this or other projects.

Furthermore, I am not an expert in fiqh or astronomy. 
I'm just listing what I've learned and observed. 
Fiqh-wise, I am strongest in the Shafi'i school, so my
comments are probably biased in that way.

Contents:
I.   Differences in Fiqh
II.  Differences in Astronomy
III. Differences in Outlying Areas

I.  Differences in Fiqh

1.  I (personally) don't know of any fiqh difference
in computing fajr.  The position of the Shafi'is and
the strongest position of the Hanafis is that it is
when a white light spreads horizontally across the
horizon.

1a.  For sunrise (which is significant because it
marks the end of fajr), it is when the least part of
the sun rises above the horizon.  There has been some
concern that some calculation methods use the time
when the sun is mid-disk above the horizon, which is
obviously not what we're after.

2.  For dhuhr, the Shafi'is and Hanafis I have
observed have no qualms about praying a short while
after zenith, which is a well-known computation. 
(Actually, many prayer calendars list zenith time as
dhuhr, which is not quite accurate.  One is not
allowed to pray when the sun is at its zenith, but in
the Shafi'i school, one can pray almost immediately
after this.)  However, the Malikis I have observed
delay dhuhr quite a bit.  I don't know their fiqh
criterion, but could probably find out.

3.  For asr, the three schools: Shafi'i, Hanbali, and
Maliki pray when the length of the shadow of an object
is the length of the object plus the length of the
shadow when the sun is at its zenith.  The dominant
position of the Hanafis is when the length of the
shadow is twice the length of the object.  (I don't
know if the Hanafis require one to add the length of
the shadow at zenith to this.)

4.  For maghrib, there really isn't a difference of an
opinion, so long as one is sure the entire disk of the
sun is below the horizon.  Some calendars apparently
list sunset as when the sun is mid-disk below the
horizon, which is plainly wrong.

5.  Personally, I find that most prayer calendars are
seriously lacking in computing isha according to the
Shafi'i school.  Isha in the Shafi'i school is when
red twilight has disappeared.  The dominant position
of the Hanafis is that it occurs when *white* twilight
has disappeared.  The difference is enormously
significant.  I'm not sure what the other schools say.
 Furthermore, what I have listed here as the Shafi'i
position is the position of fatwa within the school.

II.  Differences in Astronomy

The differences in astronomy only affect computation
of  fajr and isha times in my experience.

1.  For fajr time, there is a wide array of opinions. 
MWL (The Muslim World League), the majority of
Indo-Pakistani scholars of fiqh, and Sheikh Nuh Keller
(an American living in Jordan who went out to the
Jordanian desert to measure prayer times) have
published that the correct value is when the sun is 18
degrees below the horizon.  ISNA (The Islamic Society
of North America) uses a value of 15 degrees.  I have
seen some other opinions as well.  The ISNA fajr is
far later than fajr according to the other means.

2.  For isha time, ISNA also uses a value of 15
degrees and bases this on the Hanafi definition of
isha.  In one of its decrees, MWL declared isha to
enter at 17 degrees based on the Shafi'i definition of
isha.  This cannot be reconciled because Shafi'i isha
is supposed to be far earlier than Hanafi isha and a
value of 17 degrees will yield a later isha.  I have
seen other values used, such as 18 and 19 degrees. 
However, all of these values seem far too late for the
computation of Shafi'i isha.  Go out to where you can
have clear view of the western horizon on a clear
night and observe for yourself when the red
disappears.  (Not the yellow, but the red.)  You will
find it disappears even earlier than the time listed
for 15 degrees.  Some research and publication is
needed in this area.

Note: using 18 degrees for fajr leads to an *earlier*
time than using 15 degrees while using 18 degrees for
isha leads to a *later* time than using 15 degrees. 
The proof of this is left as an exercise for the
reader.  :)
 
III.  Differences in Outlying Areas

In some parts of the world, prayer times are not
easily computable.  In Vancouver, there is no Hanafi
isha in the summer.  Furthermore, no published value
of fajr will work during some summer nights.  Even
before the calculatins stop working entirely, one
finds fajr times of approximately 1:30 am using the 18
degree value!  Fuqaha and astronmers have spent a lot
of time writing up on how to compute prayer times for
these areas.

However, this is an area that I don't have a lot of
knowledge about.  I have read some of what the
classical Shafi'i fuqaha have written but I need to
sit with someone knowledgeable in both fiqh and
astronomy to translate the classical works into modern
calculation methods.

MWL outlined an algorithm in a decree (which I
translated) that makes computing prayer times for
areas like Vancouver easy.  The decree states fiqhi
definitions and then translates them to astronomical
terms.  However, upon further observation, I began to
doubt that the scholars who signed it actually agreed
with the astronomical statements.  I have a feeling
that they were just agreeing with the fiqhi statements
in it.  I began to get the impression that all the
astronomical statements boiled down to the conclusion
of one amatuer astronomer who wasn't a faqih.  

There are a bunch of other algorithms that have been
devised, but I'm not very familiar with them. 
Furthermore, I'm not really comfortable following a
calculation method unless it's based on a classical
text of fiqh while its translation into modern
astronomical terms is approved by a scholar authorized
to teach the text.

Salam,
Moustafa


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