Certainly, Allah after creating the sun, the earth and the moon has not left them to wonder at random, rather they move within an organised, fixed pattern without any scope or margin for error or variance as a basis for the calculation of time and the calendar.
Appreciating this fact (movement of the moon, earth and the sun are the basis of calculting time and passing thereof), the question that arises is that to what extent has atronomy secured this information; how reliable is it and what components thereof can be proven conclusively without a reasonable doubt.
In response to the above question, experts in the field have proven that the undermentioned aspects can be established conclusively, without a shadow of doubt with relative ease:
1. The time of conjunction (when the moon, the sun and the earth are in a straight line) can be calculated to the second;
2. Altitude of the moon in relation to the horizon or observer can be calculated to the degree;
3. Azimuth – the direction of the moon, measured clockwise around the observer’s horizon from the north. So, when the moon is due north it has azimuth of 0 degrees, when due east 90 degrees, South 180 degrees and West 270 degrees;
4. Elongation of the moon, i.e. it’s angular separation from the sun;
5. The phase, width and age of the moon;
6. Astronomical sun and moon rise and set times (which are already relied upon for selective purposes).
Although the above can be established conclusively, certain aspects that are pertinent and critical to the issue of moonsighting cannot be conclusively proven and are the facts of personal experience and research which may be questioned or debated. Amongst them are:
Firstly, the Danjon limit of visibility of the lunar crescent, i.e. what is the minimum degree of elongation at which moonsighting is possible? Named after Andre Danjon, an astronomer who in 1932 announced based on research and experience that at an elongation of 7 degrees or less, moonsighting is impossible. The Malaysian Professor Muhammad Ilyas is of the opinion that an elongation of 10.5 degrees or less will not allow moonsighting. Of late, research at the department of Physics, University of Durham, has shown this limit to be 7.5 degrees. They have attributed the finding of Andre Danjon to an imprudent estimate and that of Professor Ilyas to the underestimation of the power of sight.
Resulting from the above differences of opinion, a deduction that may be made, although not conclusive but very persuasive, is that the elongation limit of visibility is at least 7 degrees (as this is what all parties are agreed upon). A reported sighting of less than 7 degrees will be unacceptable according to all.
Secondly, the altitude of the moon in relation to the horizon can be calculated accurately to the hundredth of a degree. However, the minimum altitude at which point moonsighting is possible is speculative. Experts have asserted that at an alttitude of less than 5 degrees moonsighting is very difficult. This is due to various reasons, amongst them:
1. Environmental conditions: the difficulty that dust, smoke, etc. in the horizon poses at a lower altitude is greater than at high altitute.
2. Seasonal conditions – the difficulty that mist, cloudiness, etc. poses is also greater at lower altitudes.
3. At lower altitudes, the brightness after sunset in the horizon will outshine the crescent making it difficult to sight.
Furthermore, one’s position on the globe also has a bearing such that if the moon is in the southern hemisphere, then as we move northwards, the moon will draw closer to the horizon until such a point when it will be below the horizon. At this point, it will be impossible to sight the moon because its light will not reach you. Also, at higher altitudes the density is lower, making moonsighting easier.
We, therefore, conclude that the minimum altitude at which moonsighting is possible is speculative and although experts have set a limit of 5 degrees, this may vary with changes in environmental conditions, seasonal conditions, proficiency and strength of eye sight.