Period of Tamkin
Period of Tamkin is the period of time that commences after the center of the Sun is level with (the true) horizon and ends when its following (upper) limb has descended a distance corresponding to the period of Tamkin. i.e. when its upper limb disappears below the shar’î (canonical) horizon, so that sunlight recedes from the highest hill. The shar’î horizon is the horizon seen from the highest hill of a location. The true horizon, a practical basis of astronomical calculations, is the horizon formed around the observer’s location by a flat surface imagined to go through the earth’s center at a right angle to the observer’s plumb level. In other words, it is the horizon which the imaginary plane perpendicular at the earth’s center to the line imagined to run between the observer’s location and the earth’s center, draws around the observer’s location. Time that is calculated with respect to the true horizon is called the True Time, and that which is calculated with respect to the shar’î horizon is termed the Shar’î (Canonical) Time. The true time of a certain prayer of namâz, (i.e. its time determined by way of astronomical calculation,) and its shar’î (canonical) time, differ by the amount of temporal difference between the true and shar’î horizons. This temporal difference is the Period of Tamkin.
The period of Tamkin is indispensable in the calculation of all prayer times as well as in the determination of the time of imsâk, (i.e. the time of canonical dawn, by which is also the beginning of the time of morning prayer and of the time of fast.)
Four different phenomena come together to produce the Period of Tamkin. They are: The Sun’s radius (Nisf qutr-i-shems); Refraction of sunlight (Inkisâr-i shu’â’-i-shems); Dip of horizon (Inhitât-i-ufuq); and Horizontal parallax of the Sun (Ikhtilâf-i-manzar). Addition of the first three of these components and subtraction of the fourth one from the sum, yields the Period of Tamkin. The four phenomena are explained in the following paragraphs:
1- The Sun’s Radius (Nisf qutr-i-shems): Prayer times in true time system are determined by way of astronomical calculations, which in turn are based on the plane of true horizon. The plane imagined to be intersected at a right angle at the center of the earth by an imaginary line connecting the observer’s feet to the center of the earth, (i.e. by the plumb level,) is termed the ‘plane of true horizon’. Since the so-called astronomical calculations are based on the center of the Sun and on that of the Earth, an ante meridiem alignment of the Sun’s center with the true horizon is (an astronomical) “sunrise”, while an identical alignment is said to be “sunset” when it occurs within the post meridiem hours. However, the upper half of the Sun is above the true horizon at both of these mathematical instants of sunrise and sunset, and therefore half of the Sun is within the observer’s view. For this reason, the Sun has already risen by the supposed time of sunrise; nor has it set yet where astronomical computations say that ‘the Sun has set’. For, half of the Sun is ‘already’ and ‘still’, respectively, above the horizon. This phenomenon is the first component feature in the Tamkin. Accordingly, sunrise (with respect to true horizon) should mean that the upper (preceding) limb of the Sun rises above this horizon, and sunset requires that the upper (following) limb disappear below it. Then, both at sunrise and at sunset the Sun should be further down by its radius. Whereas astronomical calculations are based on the center of the Sun, its upper limb is essential in prayer times. The difference between the two time systems is equal to the radius of the Sun. That is, both sunrise and sunset require that the Sun be lower by an arc equal to its radius.
2- Horizontal Refraction (Inkisâr-i-shu’â’): The astronomically calculated place of the Sun is lower in comparison to where it is observed to be. In other words, the naked eye perceives it to be somewhat higher up than where astronomical calculations say it is. The reason for this difference is a series of refraction that sunlight undergoes as it travels through various different layers of atmosphere before it reaches the observer’s sight. On account of this event of refraction of light, the entire Sun is seen above the place it should be according to the calculation. This difference due to refraction of light is the second factor contributing to the period of Tamkin. That means to say that the entire Sun should move down by an arc corresponding to this difference both as it rises and as it sets.
3- Dip of Horizon (Inhitât-i-ufuq): Prayer time calculations for a certain city are based on a horizon observed from the highest hill of that location. At a time of evening or sunset determined by calculation, observations made from various elevations would reveal that the Sun had not set yet. This fact shows that the shar’î (canonical) horizon seen from the highest elevation of a location is lower than the true horizon essential in astronomical computations. For that matter, commencement of the time of evening prayer, which is also the time of iftâr, (i.e. the time when fasting Muslims can and must break their fast,) is not the sunset with respect to the true horizon, but the Sun’s disappearing below the shar’î horizon of the location. The horizon seen from the highest elevation is called the Shar’î (canonical) Horizon.
Astronomical calculations do not include this element of Tamkin. For, astronomical calculations are done on a sea-level basis, and data and other quantitative information thereby obtained are publicized through annual calendars called almanacs. Prayer times in a certain city, on the other hand, concern the entire city and must therefore be calculated and publicized in such all-embracing circumspection as to make sure that daily prayers performed by all the citizens, including Muslims living in the most elevated districts, be (performed within their correct periods and thereby be blessed with the canonical acceptability called) sahîh (in Islamic terminology). Settlements and cities are not flat like plain and sea surfaces. Land is mostly uneven. Elements to be used in the calculation of imsâk and other prayer times, e.g. sunrise, sunset and altitude of the Sun, should be based on the shar’î horizon, i.e. that which is with respect to the highest elevation of the city in question. Since the shar’î horizon is lower than the true horizon used in astronomical measurements, the Sun must descend further so as to disappear out of sight below this canonical horizon, and sunrise in this sense is the first sighting of the Sun on this horizon, which is, again, lower in comparison to the true horizon.
In short, sunrise with respect to the shar’î horizon is earlier by a length of time obtained by adding these three elements and subtracting the parallax from the sum, than sunrise with respect to the true horizon, while sunset is symmetrically later.
4- The Sun’s Horizontal Parallax (Ikhtilâf-i-manzar): Is the angle that would be formed at the center of the Sun by two straight lines imagined to diverge from the Sun’s center, one in the direction of the center of the Earth and the other tangential to the Earth’s surface; its angular value is 8.8”, which is merely an infinitesimal value and has a token effect on the result. In short, parallax, or ikhtilâf-i-manzar, is an angle subtended at the center of the Sun by the radius of the Earth. It is the Earth’s surface where people live; yet calculations are carried on in accordance to its center. Parallax, in contrast to the previous three elements of Tamkin, retards sunrise and advances sunset; therefore the period of Tamkin is determined by subtracting parallax from the sum of the other three elements.
Islamic astronomers calculated different periods of Tamkin for different latitudinal degrees, and published the tables thereby prepared in their works. One such table of Tamkins will appear on the screen when the cursor brought over the blue-coloured Table of Tamkins is clicked. The periods of Tamkin ought to be used in the computations of prayer times and imsâk as an inevitable requisite of the science of astronomy.
A city has virtually one shar’î horizon and one period of Tamkin. The period of Tamkin in a city, as it has been calculated as per its highest elevation, cannot be changed. Nor are there different periods of Tamkin for different prayers. (In other words, the same period of Tamkin is to be applied to all five daily prayers all the year round.) If a period of Tamkin is pared down, the early afternoon prayer and all the following three prayers will be performed prematurely, while Muslims will begin their fast after the time of sahûr (imsâk, fajr). Prayers of namâz performed earlier than the commencement of their prescribed time and fasts commenced after the Islamically established time of fajr are not sahîh, (which means that it is as if one had not performed the so-called acts of worship at all). Period of Tamkin has by no means anything to do with an extra period imposed for precautional considerations. It is written in Durr-i-Yektâ, (a celebrated book of fiqh written by Imâmzâda Muhammad Es’âd bin Abdullah of Konya [d. 1264 (A.D. 1848)] ), that if a fasting Muslim (goes on eating and thereby) delays the commencement of his daily fast by three or four minutes after the time of imsâk on the wrong supposition that the period of Tamkin is intended for precaution, his fast will be fâsid, (i.e. an entire day’s act of worship will be null and void).
TIME CALCULATION DIRECTORATE