Syed Khalid
Shaukat
This is an attempt to
present a clear perspective of the science of moonsighting and to clarify some
of the misconceptions and wrong perceptions about moonsighting that people
always talk about. Let us talk about the misconceptions
first.
Misconception 1:
29th day moon is always thin and 30th day moon is
thick.
This is myth. The thickness
of the moon depends upon how far west your location is from the point the moon
is born or from the point where it was first visible. The moon that is first visible in
Thailand will be thin but the same moon on the same day in USA will be
thick. However, if the moon is
first visible in Morocco then it will be thin in USA. In fact it is very possible that the
30th day moon of one month is about the same thickness as 29th day moon of
another month viewed from the same location. It is explained better in Figure
1.
The
moon revolves around the earth in an elliptical orbit, therefore, sometimes it
is closer to the earth and sometimes it is farther from the earth. In Figure 1, the left hand side picture
is an example of 29th day moon of one month when it is closer to the earth and
its age is 20 hours, while the right hand side of the picture shows 30th day
moon of another month that is farther from earth with the age 25 hours. To an observer from earth, both of these
crescents would appear to be about the same thickness.
Misconception 2:
29th day moon sets in a short time while 30th day moon remains longer on
the horizon.
This is another myth and can
be clarified with the help of Figure 2.
The horizontal line is representing the horizon of an observer from earth
looking for the moon. In the left
hand side picture the 29th day moon of one month is closer to the horizon but
moves along a slanting path and eventually sets below horizon. In the right hand side picture the 30th
day moon of at another location is higher above the horizon, but moves almost
vertically downwards and takes less time to go below horizon as compared to the
left hand side case. Therefore, it
is not correct to say that the 30th day moon remains longer on the
horizon.
Misconception 3:
If the moon is thick and remains on the horizon a long time, it must be
the 2nd day moon.
This is very common argument
that we hear repeatedly, but has no truth in it. This can be clarified with the help of
Figure 3. If on the 29th day, the
moon at sunset is 18 hours old and is higher above the glare of the sun, it may
be visible on that day and will appear to be very thin. However, if the 18 hours old moon on the
29th day is very low on the horizon, it would not be visible on that day, then
on the 30th day it would be 42 hours old and quite thick, and remains above the
horizon a long time, but it was not visible the day
before.
In
Figure 3, the left hand side is 29th day moon when it is 18 hours old and is not
visible because it is very close to the horizon and disappears in the glare of
the sun. On the next day (picture
at right hand side of Figure 3) the moon is 42 hours old, therefore, quite
thick, and is higher above the glare of the sun, therefore remains above horizon
a long time, but it is the first day crescent, because it was not visible the
day before.
Misconception 4:
There is a dark side of the moon.
Many a times you hear the
phrase, “Dark Side of the Moon.” People think that the far side of the moon is
dark side of the moon, and that dark side faces us at the time of new moon. That is not the case. The same side of the moon always faces
the earth, sometimes illuminated, and sometimes dark. The moon takes 27 days, 7 hours, and 43
minutes to spin, or rotate, once on its axis. It takes the same amount of time to
orbit the earth. The combination of
the two motions keeps the same side of the moon facing the earth. To us on earth, the moon is fully
illuminated at full moon, completely dark at new moon, and partially lit in
between.
Misconception 5:
Three consecutive months of 30 days are not
possible.
Three consecutive months of
30 days are very possible and are not uncommon. In fact even four consecutive months of
30 days is possible, but rare. Moon
completes its cycle around the earth in 29 days 3 hours to 29 days 20
hours. Those longer cycles (i.e.,
29 days 20 hours) sometimes occur in a row for 4 consecutive months because of
the position of the moon in its orbit.
This will result in 3 or 4 consecutive months of 30 days each.
Moonsighting.com has documented the moonsighting for every month for various
locations throughout the world spanning last two decades, and confirms that
three consecutive months of 29 days, and four consecutive months of 30 days have
occurred several times at any one location.
Misconception 6:
Full moon occurs on the 14th night.
This is wrong too. Full moon is the instant of time when
the earth is between the moon and the sun in the same vertical plane. This could happen at any moment of day
or night. Therefore, it is very
possible that in one month the moon is full at 7:00 AM. This moon would be 99% lit on the night
before and becomes full in the morning, but decreases to 99% lit-up on the
following night. Such a moon would
appear as a full moon to an observer on both nights. These two nights could be 13th and 14th,
or 14th and 15th depending upon the location on earth and the new moon birth
universal time.
MAIN FACTORS FOR CRESCENT
VISIBILITY
Most people associate
visibility with the age of the moon.
Age of the moon is simply the time lapsed since new moon. The crescent formation depends upon the
angular separation of the moon from the sun as seen from the earth. As the time passes from the instant of
new moon, the moon moves slower than the sun appears to move (because of
rotation of the earth). This causes
the angular separation between the sun and the moon and the formation of the
crescent. This may be explained
better with the help of Figure 4.
Figure 4 shows a space view
of sun, moon, and earth. The earth revolves around the sun in an elliptical
orbit, with the sun off-center, and the moon revolves around the earth in a
similar way. When the new moon
occurs, the sun, moon, and earth come in line as shown, and no light of sun
falling on moon can come to the earth, so it is a dark or invisible moon. About 18-24 hours after new moon, the
moon moves away from the line of earth and sun, to its new locations as shown by
the location of the crescent moon. Now sun and moon have separated from the same
line. The angle subtended by sun, earth, and moon is the "angular
separation." This angular
separation causes the crescent to form. Until this angle becomes 7 degrees, no
light of sun reflected by the moon can come to the earth, because of the
mountains on the surface of the moon that block the sunlight (Danjon 1932). This angle must be at least about 8.5
degrees for the sun's light to reflect from the moon making a thin crescent that
can be spotted with high-powered telescopes. For naked eye, this angle must be at
least about 10.5 degrees.
Sometimes, this crescent is very thin, very low on the horizon, so it
cannot be seen as it disappears in the glare of sun, and therefore is not
visible, even though it may remain above horizon for 20-30 minutes after
sunset.
Another important factor is
the moon's altitude above horizon. This is due to the curvature of the
earth. Moon may be in the southern
hemisphere and from northern hemisphere it may be very close to the horizon and
at even more northern areas it will be below horizon. This happens in the month
of September and October in USA, when the moon is in the southern hemisphere,
therefore, it can not be seen from northern hemisphere. If the moon is above the
horizon but close to it within the glare of the sun, then it may not be
visible. The moon within the
altitude of 5 degrees is usually not visible.
For
a sightable crescent from any location, the following parameters are most
important:
1.
Angular separation of moon from sun as seen from earth. (This is also
called elongation, or arc of light, or simply angle from
sun)
2.
Moon's altitude above the horizon.
It
is also a scientific fact that, if the moon is visible anywhere on the globe, it
would be more easily visible on all places west of it. On the contrary, we hear
the news of moonsighting in Middle East, and on the same evening, here in North
America several hours later, it is not visible despite clear horizons. This is against known scientific
facts. This clearly tells us that
what was seen in Middle East could not have been the moon.
Muslims astronomers in this
age of technology are now in a position to calculate the dates for
possible/impossible moonsighting.
So the validity of sighting claims can be easily verified for correct
moonsighting. To start an Islamic
month correctly, we must examine sighting claims in light of knowledge that
Allah (SWT) has given us. Let us pray to Allah (SWT) to open our hearts and minds to
understand these facts about moonsighting.
Let us further pray to Allah Almighty that He may guide us to the right
path, forgive us for our mistakes and make us united in the way He pleases,
Ameen.