Hilal Spotting
Posted on Monday 9 October 2006 to unknown
The Islamic calendar is the only one in use in the world today that can be truly described as a
lunar calendar. That is, every month is synchronized to the cycle of
the moon and not the solar year.
Others that purport to be lunar-based such as the
Hebrew and Chinese ones, while certainly being based on lunar
months also contain mechanisms designed to
synchronize them with the solar year. Hence they are more properly
described as lunisolar calenders.
The Islamic calender on the other hand is never synchronized with the solar year because
from
its inception, special measures were taken to actually prevent this
correction process from taking place. The intention behind this was to
remove the need for expert knowledge when it came to determining the
times and dates of religious observance, something that in the past had always
been associated with the work of priests. This was a conscious decision
by the founders of Islam as a way to prevent the rise of a
priestly class or Church establishment within Islam, something to set it apart from other
religions1.
In the 9th year after the Hejira
(Muhammad's migration to
Medina in 622 and the starting date of the Islamic calendar), the
Prophet forbade the insertion of leap months which used to occur in the
traditional Arabic calender:
The postponing (of a Sacred Month) is indeed an addition to
disbelief: thereby the disbelievers are led astray, for they make it
lawful one year and forbid it another year in order to adjust the
number of months forbidden by Allah, and make such forbidden ones
lawful. The evil of their deeds seems pleasing to them. And Allah
guides not the people, who disbelieve. This Ayah prohibits such
practice.
(Al-Taubah 9, Ayah 37)
Solar calendars,
it could be argued, are by the nature of their complexity, the
product
of either wealthy church establishments or of powerful states
and their
maintenance has over the centuries taxed the efforts of a great many
priests, astronomers and mathematicians. In a way they oblige obedience
in worshipers to some authority (i.e. governemtn or church)
which could therefore be seen as mediating their relationship with
their deity.
The movement of the
moon,
on the other hand (and by the same argument), has always been owned by
the
common people who have never needed anyone to tell them what phase the
moon was in at any moment. This is seen by the
adherents of Islam as a demonstration of its greatest strengths: its
simplicity, universality and its fundamentally anti-elitist character.
Ibn 'Umar (Radiya-Allahu 'anhuma) reported that the
Messenger said: "We are an illiterate nation. We do not use
astronomical writing
or computation [in our fasting]. A month is so and so and so (and he
pointed with his hands three times, folding the thumb on the third
time, meaning twenty nine days) or so and so and so (and he pointed
with his hands three times, meaning thirty days).
(Bukhari, Muslim, Abu
Dawud and An-Nassa'i)
The Islamic year, as with other calendar systems, is the completion of
12
months. A month is based on the cycle of the moon and can be no shorter
than 29 days and no longer than 30. This means
that the Islamic year is about 11 days shorter than the solar
year and, as a consequence, the lunar months drift backwards through
the
solar
year without paying any heed
whatsoever to the season. Before the Islamic calender came into effect,
the ancient Arabic month of Ramadan
had originally
referred to the hottest month of year (from ramda meaning "hot
stones"). Now it can fall at any time in the solar year and in any
season. It takes
lunar 33 years
before the Islamic calendar realigns itself with the solar year once
again.
While this slippage is predictable and can be calculated many
years in advance, another feature of the Islamic calendar is far less
deterministic: the exact day on which a month begins.
Technically, an Islamic month commences at the time of the first
sighting (by two Muslim witnesses) of the crescent moon (the Hilal)
which occurs after a new moon. This becomes especially important at the
start of the holy month
of Ramadan because it marks the beginning of a month of fasting and
of other rituals.
?Whoever
witnesses the crescent
of the month, he must fast the month.?
(Qur'an, 2:185)
?If you see the Hilal, then fast, and if you see
it (at the end of Ramadan), then break your fast, and if the sky is
overcast, then fast thirty days.? (Muslim/Bukhari)
?A month is
either 29 or 30 days long. So if you see
the
Hilal, then fast, and if you see it again (at the end of Ramadan) then
break your fast. And when the sky is
overcast, then complete the
count (of thirty days).?
(Nasai)
Based on such a simple criteria, you'd
think that there would be no difficulty in ensuring automatic unanimity
amongst observers of the start of a lunar month. In practice, however,
it turns out to be an extraordinarily difficult astronomical problem
because unlike other celestial events this one must also take into
account the question of human visibility. It's not enough to simply
refer to
calculations in order to say that something or other has happened, it
must also have been
observable by someone.
A new moon is the conjunction of the earth, moon and sun, this
means that their centres all lie in exactly the same line. Under these
conditions the moon becomes invisible when viewed from the earth
because the side of the
moon that is being illuminated by sunlight does not face the
earth. As the moon moves in its orbit away from conjunction, some of
sun's
light hitting the moon starts to be reflected toward the earth
illuminating an edge of the moon which then appears as a crescent. As
the
month wears on the proportion of moon visibly
illuminated increases until the 14th day, otherwise known as the
full moon. From then until the end of the month the moon is on the wane
with the crescent receding to the other edge of the moon until it
finally disappears altogether. This is yet another new moon.
This is a New Moon. It just so happens to be in front of the Sun. Not
all new moons pass in front of the sun. Usually the moon passes above
or below the sun when it is new or "zero days old". This is an eclipse
photo from June 10, 2002 8:49 pm EDT through a 6" f/8 telescope. [Moon
Photo Page]
|
The problem with first spotting the Hilal
is that at the time of the conjunction, the moon is located at a point
in the sky that is very
close to the sun, usually it is just above or below it and very
occasionally directly in front of it, as in the case of an eclipse. As
it moves out of conjunction, the tiny amount of light coming from the
sliver of
the new crescent is
completely swamped by the glare of daylight and making it invisible to
observers on the earth. The earliest time that the crescent can be
observed is after sunset and even then only once the twilight
has decreased to
a point where the crescent light is brighter than it. By the time the
moon is finally visible, it is already likely to more than twelve hours
"old",
that is it would have been at least twelve hours since it left
conjunction with
the earth and sun. The world record for observing the youngest crescent
is 15.4 hours with naked eye, 12.7 hours with binoculars, and 12.2
hours with a telescope.
This is a one day old moon. More precisely, it's 1 day 15 hours and 35
minutes. That's how much time has passed from the moment of New Moon
till this picture was taken. One day moons can be difficult to spot.
They are very close to the horizon
and visible for just a few minutes after sunset. This moon was 39 hours
old.
This picture was taken
with a Nikon Coolpix 885 digital camera held up to the eyepiece of a
Celestron C-90 Astro telescope on July 11th 2002 at 10:03 pm EDT in
Holt, Michigan. [Moon
Photo Page] |
Because the moon is still very close to the sun, there's hardly any
time
to observe the Hilal before it promptly sets as well. Under
even the very best conditions
the crescent might be visible for up to an hour after sunset but
usually
this time is much shorter, often only a few minutes. If the moon is
younger than 12 hours it is unlikely to be visible at all.
Atmospheric conditions and weather patterns can have a major impact on
the
observation, of course, but there are many other factors to
consider as well:
the latitude and longitude of the observer, the position of moon in its
orbit (because of moon's orbit is tilted with respect the plane of the
earth's orbit around the sun making crescent more or less obvious) and
even the lunar mountains can
have an effect by casting shadows onto the tips of the
crescent! The longitude of the observer matters in the a relative sense
that if observers to the East have failed to sight the Hilal,
there
is still a chance that observers further to the West will manage it.
That's
because the
moon will have had more time to move out of conjunction before sun sets
in that part of the world.
Latitude is also important because at the time of the vernal equinox
(March in the Northern Hemisphere, September in the Southern) the sun's
path is steeply perpendicular to the horizon, i.e. the sun comes
straight down when it sets rather than moving down diagonally. This
steepness of descent means that
the crescent moon will be higher in the sky just after sunset, thereby
improving its visibility.
In cases where there has been a failure to sight the Hilal then
the old month (Sha'ban in the case of Ramadan) is not considered to
have ended yet and it automatically runs to 30 days, potentially creating
disagreement amongst observers. The only thing that is certain is
that the previous month is never shorter than 29 days and that the Hilal
cannot ever be observed before the new moon.
Who claims that he viewed the thin waxing crescent
before the New Moon instant, is like the one who claims that he saw the
Sun before dawn, or he saw the baby before delivery. (proverb)
This is the back door in which calculation and computation reenter the
picture. Web sites like Moonsighting.com
run a service not unlike a weather bureau in which they forecast Hilal
visibility information based on calculations made by Dr. Monzur
Ahmed's MoonCalc
program.
Here is the forecast that was issued for the Ramadan of 2003
Ramadan: The moon's conjunction is
on
Saturday October 25, 2003 at 12:50 UT i.e., 8:50 am Eastern Daylight
Time - 5:50 am Pacific Daylight Time. On Oct 25, the moon is going to
be less than 13 hours old on West coast of USA, and impossible to see.
On Oct 26, the moon can be seen in most of the world, except Japan,
Northern Asia, and most of Europe. In England, it may not be seen even
on October 26, although it is going to be 28 hours old, because it will
be only 3 degrees above horizon at sunset and the glow of sunlight will
make it very difficult to see.
The first day of Ramadan will be on October 27,
2003 for Australia, Africa and Americas, and on October 28, 2003 for
Japan, Northern Asia, and most of Europe. England is in a situation
that moon may or may not be seen on October 26.
This was then followed up by an announcement made about the starting
date by the Islamic Shura Council of North America
The Islamic Shura Council of North America and Fiqh Council
of North America, of which ISNA is a member, agreed that there were no
confirmed moon-sighting reports on the evening of Saturday, October 25,
2003, the 29th of Sha'ban. We will complete 30 days of Sha'ban.
Therefore, Monday, October 27 will be the first day of Ramadan in North
America. Ramadan Karim
To get a sense of the difficulty of spotting the new crescent moon, you
could try your hand at simulating it using Helmer Aslaksen's very nice
(and very simple to use) Java applet entitled "What
does the waxing or waning Moon look like in different parts of the
world in the course of the year?".
First set the month to the one you want to observe (let's say October) and
then set
the day of the month to 1. Choose your location in the world from the
map and then turn the speed down to really slow (the default speed is way
too
fast). You will probably also want to "freeze" the day so that you can
watch it in a loop over and over again because the Hilal happens
so quickly.
The program makes some fairly drastic simplifications, especially that
the moon and sun orbits are on the same plane but there's still plenty
of complexity here to contend with even with such a simple model.
I made the animation below by
capturing frames generated by the applet. This is how the crescent
would appear if viewed from Melbourne in the month of October.
The institution of Gregorian
calendar in 1582 was made necessary in order to stop seasonal drift in
the date of Easter. This date was originally agreed by the First
Council at Nicaea to be calculated as falling on the Sunday following
the first full moon that follows the Northern Spring equinox. The
problem was that with the Julian calendar, the equinox was drifting
forward from year to year, even by the time of the First Council in 325
(only 371 years after the Julian calendar had been established) the
equinox drifted 4 days from its traditional date of the 21st of March.
By 1582, this drift had grown to ten days which was an intolerable
situation and had to be remedied and despite religious schism, even
protestant Europe agreed (very gradually) accepting the reforms
although without accepting Catholic religious primacy.
