The New Nation - Internet Edition

Prof. Dr. Anwar-ul Karim

The lunar phase depends on the moon's position in orbit around the earth. In astronomical terminology, the new moon is the lunar phase that occurs when the moon, in its orbital motion around the earth, lies between the earth and the sun and is in conjunction with the sun as seen from the earth. The moon then lies in the same direction (longitude) as the sun when viewed from the earth. At this time, the illuminated half of the moon faces directly towards the sun, and the dark or unilluminated portion of the moon faces directly towards the earth, so that the moon is invisible as seen from the earth. Full moon occurs when the moon comes into conjunction with the sun when it passes behind the earth. Fig. 1. The moon when first seen as crescent after conjunction with the sun, the time of its appearance is the young crescent's visibility. Intricate physical principles are involved in the excercise of the earliest visibility of the young lunar crescent. These are of optical nature, involving the properties of the human eye as a radiation receiver and the illumination characteristics of the young crescent and the background sky. The latter depends upon the relative solar position. Optical aid (binacular, telescope, etc.) and the height at which it is used (ground level or elevated e.g., in a plane) will affect the eye's ability to register a low illuminating crescent source. Optical characteristics of the human eye will vary from person to person and also may vary with circumstances.

The earliest astronomical criterion for ascertaining the crescent's first visibility goes back to Babylonian era. The simple criterion based on the observational data was used by early astronomers. The Babylonian criterion is more a rule of thumb which may be stated as follows:

1. At local sunset, moon's age must be more than 24 hours i.e. from the time of conjunction to the time of evening of observation.

2. Moonset should take place at least about 48 minutes after sunset.

Sightings of moon younger than 20 hours are rare and sightings of moon older than 24 hours are not uncommon although the visibility may at times require it to be more than 30 hours old.

The moonset lag criterion is simple enough and is perhaps more meaningful to a layman who can now. easily understand that the local moonset should follow considerably after the local sunset and never before (i.e. conjunction must take place before the local sunset) and can easily estimate the chance of visibility on a local evening reasonable accurately.

The motion of the moon in its orbit is very complicated and its period is not constant. Moreover, Islamic calendar starts a month with the first appearance of the thin crescent of the new moon after sunset over the western horizon. The date and time of this actual observation depends on the exact geographical longitude as well as latitude, atmospheric conditions, the visual acuity of the observers, etc. Therefore, the beginning and lengths of months in Islamic calendar cannot be accurately predicted.

The new moon is often considered to occur at the time of appearance of the first visible crescent of the moon, after conjunction with the sun. This takes place over the western horizon in a brief period between sunset and moonset, and therefore the precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer. The astronomical new moon, sometimes known as dark moon to avoid confusion, occurs by definition at the moment of conjunction in ecliptic longitude with the sun, when the moon is invisible from the earth. The moment is unique and does not depend on location. The first visible new crescent is the beginning of the month in lunar calendars such as Muslim calendar. The time interval between new moons is about 29.53 days. The lunar phase midway between the new moon and full moon is called the first quarter as it marks one-quarter through the month. Similarly, the lunar phase midway between the full moon and new moon is called the third quarter as it marks three quarters through the month. Fig-1.

It is interesting to note that the astronomical new moon occurs, by definition, at the moment of conjunction in ecliptic longitude with the sun and at that moment the moon is completely invisible from the earth. On full moon, as the name signifies, the moon is observed to be fully illuminated. The quarter moon is actually precisely one-half illuminated on both the lunar orbital phase of first and third quarter. Between new and full moon, the illumination is increasing from night to night, so the moon is said to be waxing. Similarly, between full and new moon, the illumination is decreasing night to night, so the moon is said to be waning. Between third quarter and first quarter, less than half of the moon is illuminated, so the moon is crescent shaped. Between first quarter and third quarter, more than half of the moon is illuminated and so the moon is said to have a gibbous shape.

Fig 1 also indicates that a planet comes into conjunction with the sun when it passes behind the sun (superior conjunction) or between the earth and the sun (inferior conjunction). It then lies in the same direction (longitude) as the sun when viewed from the earth. An inferior planet (one orbiting closer to the sun than the earth) alternately passes through both inferior and superior conjunction; a superior planet (one further from the sun than the earth) can come only to superior conjunction.

The phases of the moon are determined by the position of the moon in its orbit around the earth, which in turn determines how much of the sunlit moon is seen from the earth. In Fig 1, when the moon is behind the earth, we see the moon as full. In the same figure, when viewed from a point over the earth's north pole, the earth both rotates and revolves in a counterclockwise direction. From this viewpoint, the moon also rotates on its axis and orbits the earth counterclockwise.

The time interval from one new moon to the next is called lunation and it is variable. Lunation number is a number given to each new moon beginning from a certain one in history, usually but not always taken to be the first new moon of 1923.

An approximate formula has been proposed to compute the mean moments of new moon (conjunction) for successive months.

Lunation numbers 1048 and 1049 are the astronomical new moons of September 2007 and October 2007 respectively. Universal dates for these two conjunctions are 254.52 and 284.21 with corresponding local day number being 254 and 284 from beginning of the year i.e., 11 September 2007 and 11 October 2007 respectively. Thus the Shawwal 1428 astronomical new moon was on 11 October, 2007 at 5:02.

Universal Time for all over the world without depending on location of the observer.

From the Astronomical Applications Department of U.S. Naval Observatory at Washington D.C., the astronomical new moon data for the last four months of 2007 are shown in Table-I. The conjunction data are shown in universal time. They can be easily changed to local clock. Thus, add six hours to Table 1 for Dhaka time and add three hours for Makkah time, etc.

The Islamic Foundation, Dhaka, as the mouthpiece of the Govt. of Bangladesh, declared the sightings of the crescent for the last three months of the Islamic Calendar, 1428 in Bangladesh as follows:

With the above observational dates of the new moon, marking the new month when the first crescent moon is actually seen in Bangladesh, sun and moon data for those three dates are obtained from the Astronomical Applications Department of U.S. Naval Observatory at Washington D.C. Using these sun and moon data and corresponding conjunction times as shown in Table 1, moon's age at local sunset from the time of conjunction and moonset time lag which is the time difference between the local moonset and local sunset at the place of observation are easily calculated. The results are shown in Table 3 below:

This shows that moonset took place earlier than sunset on Thursday, 11 October 2007 at Makkah with no illumination of moon's visible disk. Being astronomical new moon, the dark or unilluminated portion of the moon faces directly toward the earth, so that moon is invisible as seen from anywhere on the earth. It is dark moon. But Saudi-Arabia celebrated the Eid next day, on Friday, 12 October 2007!

Like from other parts of the world, would-be Hajjees of Hijri 1428 from Bangladesh also have started pouring on Makkah. Saudis should make a very careful decision about the beginning of Zill Hajja month so that people from allover the world, many of them for only once in their life, can stand in the field of Arafat on the actual 9th of Zill Hajja; otherwise their Hajj will be spoilt ! A brief observation would be made about the coming Eidul Azha 1428 in Bangladesh. Referring again to US Naval Observatory, Washington D.C., the Sun and Moon Data for Dhaka during the month of December 2007 after the astronomical new moon are shown in Table 5.

Both the Babylonian criteria are satisfied on Tuesday 11 December 2007 at Dhaka making its probable appearance evening there for the first visible crescent of the moon. In that case Eidul Azha will be celebrated in Bangladesh, Insha Allah, on Friday, 21 December, 2007. EID MOBARAK!