Visibility of Crescents

The Moon orbits Earth once every 29.53 days (average of synodic month). Because of this revolution, phases of the Moon change as the Moon's position change relative to the Earth and the Sun. So, during the Moon's orbit, if the Moon, Earth and the Sun lie exactly at the same line and the Moon in the middle, the Sun will illuminate half of the Moon that faces it, and the other half which faces us, will be dark because it does not reflect rays of the Sun (However, due to the inclination of the Moon that might reach up to 5 degrees, it may reflect a very small percentage of Sun's rays, but according to my information no observer yet reported seeing such crescent). At this point, the Moon is called Wane or New Moon. After that, the Moon continues orbiting the Earth and begins to reflect a small amount of Sun's rays and now we see the Moon as a very small waxing crescent. Afterwards, it becomes first quarter, full Moon, last quarter, waning crescent and then wane again.

Moon's age is measured from the moment of the wane (New Moon). We often say this Full Moon is 14 days old, which means that the number of days since the wane is 14. And we say this crescent is about 2-3 days old. But, did any one ask himself what is the minimum age of crescent that we can see ? Generally, through a telescope, it is not likely to see a crescent that is less than 12 hours, i.e. if we want to observe the thin waxing crescent to determine the beginning of an Arabic month, the Moon should be in the wane phase (New Moon) 12 hours ago or more. But why?!
The wane Moon (New Moon) is located exactly at the Sun's direction, so the Sun's glare will prevent us from seeing it, in addition, the percentage of the reflected rays out of the wane Moon (New Moon) is nearly equal to zero, and this percentage increases as the Moon's age increases. Thus, GENERALLY human eye through a telescope can't detect any reflected rays from the Moon if the Moon's age is less than about 12 hours.

* When to Locate the Waxing Crescent?

The new waxing crescent is located near the Sun, so we shall wait until Sunset, because it is obviously not possible to observe the thin waxing crescent before Sunset. In addition, we must wait a reasonable time until the twilight decreases, i.e. until we can differentiate between Moon's light and twilight glare, a 10-minute period could be enough sometimes to detect the thin waxing crescent.

* Where to Locate the Waxing Crescent?

As mentioned above, the wane Moon (New Moon) is located exactly near the Sun. If we assume that the Moon will set when it is wane (New Moon), generally it will set along with the Sun, but we are looking for a new crescent, which means that it is still near the Sun. So, we must look at the west, a little bit over the Sunset point.

* When the Waxing Crescent Sets?

The Moon, like the Sun, rises from the East and sets after about 12 hours at the west (with exceptions at high-latitude areas), and since the waxing crescent lies near the Sun, it will set after the Sunset, and in its best cases, the new waxing crescent sets about one hour after the Sunset.

* Are the 12 hours only, enough as a factor to determine the crescent visibility?

Of course not. There are several factors that must be met in order to view the thin waxing crescent: Some of these factors are:-

• The crescent's altitude.
• The angular distance between the centers of Sun and Moon.
• The Moon's staying (the interval between the Sunset and the Moon set).
• The azimuth difference between the Sun and the Moon.

* What's the Meaning of Astronomical Calculations of the Crescent?

Most people think that the astronomical calculations mean absolute determination of crescent visibility, but this is not true, the astronomical calculations include the following:

1. The time of the wane Moon (New Moon) must be determined, and this time is accurately calculated. For sure there is no chance for any error.
2. Some of the above factors are determined. Such as the Moon's altitude, the angular distance between the centers of the Sun and the Moon at the Sunset, Sunset time and the Moon set time, Moon's staying period, ...etc.
3. The results of the above calculations must be compared with crescent visibility conditions in the previous years, and with the accurate practical and international observations.

* Conclusion:

The New Moon phase is defined as the instant at which the apparent celestial longitudes of the Moon and the Sun are the same. Considering the Sun, Moon, and the Earth to be points not disks. Adopting this definition, the New Moon phase is certainly a unique instant all over the world. But in reality the Sun, the Moon, and the Earth are viewed as disks not points, and so, observers on the Earth in different locations will not see the centers of the Sun and the Moon at the same longitude in the same instant. The difference may reach up to four hours. This would be obvious during a solar eclipse, which can be considered as a "visible" New Moon phase, since it is well-known that a solar eclipse does not begin at the same instant all over the world.

For most purposes, it is suitable to consider the New Moon phase as a unique instant all over the world, and so, nearly all the astronomical books and magazines publish times of New Moon phase as a unique instant, which is for the center of the Earth. But to observe the very thin crescent shortly after the New Moon phase, and to know the exact interval between the New Moon phase and the observation time (Moon's age), we should adopt the instant of the New Moon phase that occurs from the location of observation. Consequently, times of the New Moon phase in this document are calculated for Amman, or for Iraq in the Iraqi report.

Methods to Start the Islamic Months in Different Countries

There is not a unique method adopted by all the Islamic countries to start the Islamic months. There are many methods spread all over the Islamic World, some of them are:-

1. If the Wane Phase (New Moon) occurs before midnight, then the next day is the first day of the Islamic Month. This method is adopted in astronomical books and magazines and some Islamic countries.
2. If the Wane Phase (New Moon) occurs before Sunset, then the next day is the first day of the month. Since the Islamic day starts at Sunset not at midnight.
3. Some countries adopt specific criteria, such as the Moon's age, altitude, the interval between Sunset and Moon set,...etc., and if the Moon fulfills these criteria at Sunset, then the following day is the first day of the Islamic Month.
4. Some countries adopt the actual sighting of the crescent with the assistance of astronomical calculations. This is the most reliable and accepted method among people and scientists, as well as among most of scientists of Islamic Shari'a nowadays. JAS adopts this method, since the Prophet Mohammad "ASWS" ordered us not to start the month unless we sight the crescent, thus it must be seen, and we use astronomical calculations in order to know where and when to observe, as well as the probability of observing the crescent, since sometimes it would be useless to observe the crescent if the calculations show that there is no crescent in the sky after Sunset !
5. Other countries adopt several different ways, some of them make the month 29 and 30 days alternately, others make Ramadan either 29 or 30 days always, and finally some countries don't adopt any specific thing !