Why so many visibility models?
For thousands of
years, astronomers have tried to calculate the first visibility of the crescent
moon. This goes back before Islam (and the last Prophet, sallalahu
alaihi wassallam) mainly well before the Babylonian era but it is generally
accepted that the Babylonians were the main pioneers of this science.
In 358
CE the Jewish Rabbi Halel 2nd accepted Greek Philosopher Meton`s
(431BC) astronomical calculation of New moon. By introducing the
calculations, Rabbi Halel 2nd initiated opposition to the Prophetical
way of non-conditional moon sighting.
The Prophet of Islam (610 CE) not only
rejected the way (of the Metonic New moon calculation) of the Jews to start the
month but clearly taught and ordered Muslims to sight the moon in the
Prophetical manner, and that is without the use of any conditional
calculation.
However in the Islamic era of second century Hijrah after
``Khairul Qorun`` there were many scientists who attempted to introduce
calculations to predict the first visibility of New moon after Khalif Mansoor
Abbasi (136H/754CE) and his grand & great grandsons (namely Haroon786CE and
Mamoon Al Rashid 813CE) translated the Babylonian science and Greek
Philosophers’ books.
Primarily they used the Metonic calculation for
the beginning of the Islamic month, with the Moon`s sighting now depending on
the Metonic astronomical new moon theory, they would refuse witnesses without
the theory!
The Jews changed the way they performed moon sighting in the
quest to acquire the “certainty benefit” by predetermining the calendar on the
Metonic theoretical calculation for the new moon. Similarly, would be
Islamists, are in full swing to announce predetermined Islamic new moon dates
(Ramadhaan, Eid and Hajj) based on this calculation by claiming the Metonic
theory has (somehow) become more accurate than before. Is it more
accurate? No, certainly not.
To further make matters obscure (for
themselves), they argue this is not the method of the Jewish calendar.
However they must protect their principles over and above the Prophet,
sallalahu alaihi wassallam, and of course in doing so further make
matters obscure (for themselves). These so called Islamists are trying
very hard to change the Islamic path left by the Prophet of Islam and replace it
with the Metonic way of the Jews, announcing Islamic dates in advance for ease
of certainty. They argue that the fixed calendar (like the Jewish fixed
calendar) is more certain than the unconditional naked eye moon sighting method
taught by the Prophet Muhammad, sallalahu alaihi wassalam (even with the
calculations!).
As the Jews of old replaced or even omitted parts of their
religion for seeking ‘benefit’. The ‘fixed calendar’ protagonists now do
this against Islam and it`s Prophet`s true path by arguing the benefits obtained
in many communal, financial and social life. This surely means Allah, subhanahu
wata’alaa, the Creator, and His Prophet, sallalahu alaihi wassalam, the last
Messenger, never knew these benefits (La Hawl Wala Quwwat Illa
Billah).
Let us examine what their experts said before and now about the
accuracy of astronomical calculation. The most well known scientist of them Al
Biruni (973-1048 CE), concluded in his book:
"The computation of the
appearance of the new crescent is a very long and difficult
procedure."
During the modern era too despite the technological advances
many different methods have been developed which is used to justify whether or
not testimonies or shahadah from Muslims are accepted or not. But despite this
Dr Ilyas, one of the leading Muslim scientists in the field of Islamic astronomy
states:
“there are numerous ill informed astronomers assuming the role of
experts who on occasions have made claims about astronomical calculability of
the visibility far beyond the limit permitted by the then status of our standing
of the underlying physical phenomenon...the ability ‘to land man on the lunar
surface’ has been wrongly assumed to be a valid defence of the astronomical
calculability. This reflects the lack of understanding of the physical aspects
of a New Moon’s first visibility as distinct from locating the body
accurately”.
(A Modern Guide to Astronomical Calculations of Islamic
Calendar, Times and Qibla)
Even the US Naval Observatory to this day
acknowledges that:
“The visibility of the lunar crescent as a function of
the Moon's "age" - the time counted from New Moon - is obviously of great
importance to Muslims. The date and time of each New Moon can be computed
exactly (see, for example, Phases
of the Moon in Data Services) but the time that the Moon first becomes
visible after the New Moon depends on many factors and cannot be predicted with
certainty”
Despite this conclusion from USNO and Dr Ilyas and others
many Muslim astronomers, sadly both professional and amateur, attempt not just
to predict first visibility but use these visibility models to actually reject
sighting claims.
Here are some of the various visibility
models:
Babylonian: Age at sunset>24hrs & Lag>48
mins
This means >48mins (ie the difference in RA of sun and RA of moon
at sunset was >12 degrees) and moon’s age at sunset was >24 hours.
Ibn
Tariq: Alt, Lag
Well known scientist of the
8th Century, Ibn Tariq's criterion depends on moon altitude at sunset and
moonset lag.
Fotheringham: Alt, Rel Azi
In 1910
Fotheringham developed a moon visibility criterion using Schmidts observations
in Athens over a period of 20 years. Fotheringham plotted a scatter diagram of
moon's altitude at geometric sunset versus the difference in azimuth (relative
azimuth) between the sun and the moon at sunset. A curve was drawn separating
the 'visible' moons from the 'unsighted' moons. This curve was then used to
predict the likelihood of sighting young moons - if a new moon's alt/rel azi.
falls above the curve it is sightable, if it falls below the curve it is
sightable.
Maunder:
Alt, Rel Azi
In 1911, Maunder carried out some more
observations to supplement Schmidt's data and developed a model which resulted
in a curve which was lower than Fotheringhams.
Bruin:
Alt, Crescent width
In 1977 Bruin released details of his criteria
based on crescent width and sun/moon altitude. Bruin used 0.5 minutes as the
limiting crescent width.
Ilyas 1:
Alt,
Elong
Dr Ilyas developed at least three criterion. The first criterion
depends on the 'moon's relative altitude at sunset' and the angular separation
between the sun and the moon.
Ilyas 2:
Lag, Alt.
Dr Ilyas
in his second criteria compensates for latitude (eg at latitude 0 deg: lag 41
min; 30 deg: 46 mins, 40 deg:49 mins, 50 deg: 55mins).
Ilyas 3:
Alt, Rel Azi
This criteria depends on the moon's relative altitude at
sunset and the difference in azimuth between the sun and moon at
sunset.
RGO:
Alt, Elong
According to the
Royal Greenwich Observatory the best time and place for first visibility are
when the moon is vertically above the sun at sunset so that their azimuths are
equal (ie relative azimuth at sunset=0) and where the apparent altitude
of the moon at sunset is 10 degrees. If the sky is clear and the horizon is
flat, sighting should be possible just before the sun reaches a geocentric
altitude of -5 degrees.
B Yallop:
Rel Alt, Crescent Width
Professor
Bernard Yallop of the RGO used almost 300 moon sightings / non-sighting records
of the late 80s and early 90s compiled by Dr Schaefer and Doggett. A
parameter 'q' is derived from the relative geocentric altitude of the moon
(ARCV) and topocentric crescent width.
Other Models:
There are also many
other models for instance by Mohammed Odeh , Manzur Ahmed and others
(Dr.Khalid Shaukat says truly that ``his website is not in the
business of making, implementing or dictating decisions on the start of Islamic
months (Al Hamdo Lillah). See these websites:
www.moonsighting.com
http://www.icoproject.org/
www.ummah.net/ildl/mooncalc.html
So
why all these different models if, as some suggest, we have advanced so far in
predicting crescent visibility?
The truth is there are differences in
outcomes between the present day models. See Crescent Watch prediction for 19
September 09 against Odeh Criteria.
Also we know from scientists like Martin
Elsasser that the visibility models do not take into account experience of the
observer, weather conditions (and air quality) and height of the observer. All
these can make a difference when attempting to sight the first crescent, the
Hilal.
The calculations apply a average visibility model.
They do NOT take local weather conditions into account and they do not consider
local elevation. You can easily see that from the perfect curves in the
visibility graphs.
Climbing a mountain is just like climbing to better
and better weather. Climbing a mountain can drastically improve the local seeing
conditions in terms of dust and humidity and thus greatly improve your chances
to see the more difficult crescents.
On the other hand, your own body
will have more and more problems with the reduced air pressure at great
elevations and thus going to high to fast might not be useful. Example: Driving
from sea level to 4000m of elevation can be quite a problem for most
people.
Martin
So when rejecting testimonies it is important
to critically appraise the visibility model which is being used as a basis to
determine crescent visibility and not to always doubt the valid testimony of
witnesses.
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