

Notes on Moonsighting and the Islamic Calendar

The Islamic Calendar is a purely lunar calendar in which months correspond
to the lunar phase cycle. There are rules for calculating this calendar
which is very accurate over long periods of time. Dates in this calendar are
called tabular dates.

In the calculation of the tabular dates a prediction of first crescent
sighting is made, based on the width of the crescent Moon, the time of
sunset, the time of moonset, the age of the crescent Moon, the altitude of
the Moon at sunset and its bearing from the Sun.

There are times when one or more of these parameters is quite useless for
predicting whether the crescent Moon will be visible to the naked eye or
not. However based on experience we simplify the calculations by saying
that:

The crescent Moon has to be a minimum of 20 hours old at sunset The sighting
does depend upon the distance of the Moon from the Earth. When it is close
to the Earth, ie at perigee, sighting will be early, say at 18 hours old,
but when it is at apogee sighting will not occur until the Moon is at least
28 hours old.

The moonset time is not less than 20 minutes after sunset The visiblity of
the crescent Moon depends on the obsrever's eyesight, clarity of the
atmosphere, local weather, pollution level, degree of illumination around
the observer and numerous other small factors Using binoculars does not help
very much. It may enlarge the Moon, but it reduces its brightness and it is
the contrast between the twilight sky and the crescent that matters.

The Moon's elongation from the Sun is greater than 10 degrees This is based
on an ancient Babylonian rule, and is consistent with the criteria laid down
by Bruin in Vistas in Astronomy (1977), Vol 21, pp331-358, Pergamon Press.
It is interesting that the Moonwatch observations indicate that about 8
degrees could be possible and 7 degrees may be possible but maybe only once
in a lifetime.

Crescent Sighting

New Moon The New Moon phase is defined as the moment when the Moon is almost
directly between the Earth and the Sun. At this moment the Moon's dark
surface faces the Earth and is completely invisible. The exact date and time
of this invisible New Moon is commonly found in Almanacs, diaries and
newspapers.

New Crescent Moon The Islamic month begins with the first visibility of the
lunar crescent. This normally occurs some 20 hours after the New Moon.

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FAQ

What is Astronomical New Moon?

The Astronomical New Moon, or the invisible New Moon, is the moment when the
moon is almost directly between the earth and the sun. At this moment the
moon's dark surface faces the earth. Therefore it is completely invisible
even if it occurs in the middle of the night. The Astronomical New Moon
occurs every 29 days, 12 hours, 44 minutes, and 2.8 seconds. The date and
time of this invisible New Moon is commonly found in almanacs, newspapers
and calendars.

What is the relevance of Elongation in crescent sighting?

Elongation is the angular distance between the moon and the sun. At
Astronomical New Moon this angle is zero and all the sunlight reflected by
the moon surface is directed back towards the sun. With passage of time the
moon in its circular motion around the earth, moves away from the alignment
with the earth and the sun. The angular distance between the moon and the
sun increases, and some 18 to 24 hours after the Astronomical New Moon, the
moon will have moved sufficiently for the sunlight reflected off its outer
edge to be directed towards earth. The new crescent moon can now become
visible on earth.

Elongation is a critical factor in determining the crescent's visibility,
and this depends on more than just time. In the early 1930's, the French
astronomer Andre' Danjon deduced (from detailed consideration of the geology
of the Moon) that no illuminated portion of the crescent can be seen from
the earth when the Moon is 7° or less from the Sun. No sighting can
penetrate this barrier, which is set by shadows cast by the rough lunar
terrain. This is the limit of our human observational power, and below this
the crescent will be impossible to see, even with a telescope

What is the relevance of sunset in crescent sighting?

In the first sixty hours or so after the Astronomical New Moon, the sunlight
reflected by the moon is so weak that the crescent cannot be observed while
the Sun is in the sky. Generally, for sighting the new crescent, one should
start to search the sky about 15 minutes after sunset. One should look in
the direction of the setting sun, just above, or upto 30 degrees to the
right, or 30 degrees to the left of where the Sun set. One should keep
looking until the time of moonset that can be obtained from local
newspapers. Binoculars do help.

What is the relevance of moonset time in crescent sighting?

Moonset time is the time when the upper limb of the Moon is on the horizon.
If the sky is clear and the horizon is flat, crescent sighting should be
possible some 15 minutes after sunset. Quite obviously there cannot be a
crescent sighting if this is after the moonset time. The moonset time can 
be obtained from local newspapers.

Is there an accepted criterion for Crescent-sighting?

It is easy to design a criterion based on certain theories or confirmed
sightings. But it is hard for that criterion to withstand the test of actual
sighting. We have to be the judge and see if the criterion comes out true to
the actual sighting month after month, and year after year. Today our main
criterion depends on the Moon's angular distance from the Sun at sunset
(elongation) and the Moon's altitude (in degrees) above the horizon after
sunset. The age of the Moon is recorded as a guideline.

Elongation at sunset, the Moon / Sun angular separation, should be not less
than 8.1° The Crescent must be well above the horizon when the sun has
dropped 5° below the horizon. Crescent age at sunset is normally not less
than 20 hours.

When has the earliest crescent of a new moon been seen after the moon was
born?

Moon sighting does not depend on age. The authentic sightings are at about
17.2 hours with the naked eye, and 15.5 hours by observatory telescopes.
Remember, in some seasons, earliest moonsighting takes about 24 hours. So if
the moon has become 17 hours old or more, one can not conclude that it is
possible to see that moon.

What is the process one must use to correctly sight the moon?

If you know that the beginning of the month was based on an authentic
cresent sighting, count 29 days from the start date and start looking about
15 minutes after sunset. Look in the direction where the sun set, just
above, or upto 30 degrees to the right, or 30 degrees to the left. Keep
looking until the time of moonset that you can obtain from local newspapers.
Binocular helps. Have one or more persons with you, if possible. If you do
this for a few months, you will know yourself about improving your
procedure. You should keep in mind the distinction between occasions when
the Crescent is "difficult but DEFINITELY and repeatedly seen", and
occasions when the Crescent is "possibly fleetingly glimpsed but NOT
DEFINITELY seen." For the former the Crescent should be continuously visible
for at least five seconds in a sky location which is consistent from one
minute to the next and the shape of the brightening should be consistent
with the Moon-Sun angle. If in ANY doubt, accept that you haven't
objectively seen the Crescent.

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Proof of Crescent Sighting

The Marja' are unanimous that crescent sighting is proved:

When one personally sees it. By certainty or conviction. For example when
many people say that they saw the crescent, or by some other way one becomes
convinced about the appearance of the crescent. When TWO aa'dil (righteous)
male persons stand witness to the fact that they saw the crescent When 30
days of a lunar month are completed.

Ayatullah al Uzama Syed Ali al Husaini Seestani further states that:

The 1st day of any month will not be proved by the verdict of a Mujtahed and
it is better to observe precaution. (1740)

The first of a month will not be proved by the prediction made by the
astronomers. However, if a person derives full satisfaction and certitude
from their findings, he should act accordingly. (1741)

If the moon is high up in the sky, or sets late, it is not an indication
that the previous night was the first night of the month. Similarly, if
there is a halo round it, it is not a proof that the new moon appeared in
the previous night. (1742)

If the first day of the month is proved in a city, it is also proved in
other cities if they are united in their horizon. And the meaning of having
a common horizon in this matter is that if new moon was sighted in a city,
there would be a distinct possibility of sighting it in the other cities, if
there were no impediments, like the clouds etc. (1744)

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From the book: Al Fiqh Lil Mughtaribin by Ayatullah Seestani (p. 111/2)

Question 118: For establishing the beginning of some months, a few scholars
of some countries in the East declare the sighting of the moon based on the
testimony of a few who saw the crescent. However, some facts have to be
taken into consideration: a) The witnesses, who may number, say, 30, hail
from different parts of the region. For example there may be 2 from Isfehan,
3 from Qum,, 2 from Yazd, 4 in Kuwait, 5 in Bahrain, 2 in Ihsaa, 6 in Syria,
etc. b) The skies in many countries in the West are clear and believers are
actively trying to get a glimpse of the new moon since there is nothing
obstructing their view. c) The British Observatory declares that sighting of
the new moon in Britian that night without a telescope is highly unlikely.
They confirm that sighting the new moon with bare eyes may be more likely
the following night. In such a situation, how are we to act?

Answer 118: The precept here is either individual satisfaction that the moon
has been sighted or there is unquestionable evidence suggesting that it has
been sighted. In the above mentioned case and similar ones, one would not
normally be satisfied that the new moon appeared on the horizon and was seen
with the naked eye. On the contrary, one would be more satisfied that the
moon has not been sighted and that the testimonies of sightings could have
been illusions or erroneous judgement; and Allah knows the best.

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