Units of Time

Daytime (nahār) and night (layl)

Daytime (nahār) is the period that begins with the breaking of true dawn, when light starts to spread across the horizon announcing the start of new activity on the face of the earth, and ends after the night has begun, when the red twilight disappears after sunset. The night (layl) begins at sunset and extends to sunrise the next day.

But the period between sunset and the disappearance of the red twilight is a transitional zone between night and daytime, and so is the period between dawn and sunrise; each of them is a time that combines night and daytime together. This is the meaning of “merging the night into the day” and “merging the day into the night”: one entering the other gradually, not abruptly.

So daytime and night are independent entities in the order of the cosmos, not merely a direct reflection of the sun or the moon. Daytime is a temporal phenomenon tied to the presence of light, and night is a dark substance that veils the sun’s light.

So night and daytime are two independent existences that move along with these bodies without being reduced to them. God has sworn by them and by daytime and night, treating each as an independent phenomenon:

The day (yawm)

The day is a natural unit of time that begins at dawn (i.e. with the start of daytime) and ends with the beginning of the night at sunset. It does not begin at midnight as people have grown used to in modern calendars; it is a cosmic period with a definite beginning and end tied to light and darkness.

Because the moment of dawn does not occur north of about latitude 48°, the inhabitants of those regions decided that the day should begin at midnight, and this system was then imposed on the whole earth — even though those living north of latitude 48° are no more than 10% of the world’s population.

So the day begins at dawn and does not extend to the next dawn; it ends at sunset, and the night is appended to it for ordering:

The night does not precede the daytime; it follows it in a sequential order, and the basis of the reckoning is the daytime and what follows it. A precise description of nights and days as successive units came concerning the people of ‘Ad:

The month (shahr)

The month, in its linguistic and cosmic origin, is tied directly to the moon. It is not a conventional division but a natural unit of time arising from the lunar cycle.

The new moon is born at the moment of conjunction with the sun, when it is at its closest point to it and disappears from view; then it appears as a thin crescent and passes through its phases (first quarter, full moon, last quarter) until it disappears at the end of the cycle. So the month begins with a conjunction and ends with a new conjunction, lasting on average 29 days, 12 hours and 44 minutes.

The year (sanah)

The year is a unit of time tied to the sun, not the moon. It is the period the sun takes to return to the same apparent position — for example starting from its being overhead on the Tropic of Cancer and returning to it after a full cycle — and it is about 365 and a quarter days, which led to the leap year to deal with the fraction of time.

The independence of the units of time

The day, the month and the year are natural astronomical units independent of one another; each is tied to a different celestial body:

There is no direct mathematical relation between these three units, so one cannot be converted into another in whole numbers except through intercalation. By contrast, the units invented by humans — the hour, the minute and the second — are interlinked and built on successive numerical divisions (60 minutes = an hour, 60 seconds = a minute) designed to be easy to use. The natural units stand on their own and can be reduced to one another only by approximation.

An illustration: measuring length

To illustrate the independence of the units of time, compare them with units of length: the mile and the kilometre are both units of length, but they are independent at root. One mile is about 1.6093 kilometres, yet they cannot be combined in one measurement without precise conversions.

Intercalation (kabs)

Intercalation is an astronomical computation that deals with the fractions of time arising because the natural units (day, month, year) do not match whole numbers of days. It is keeping the fractions and accumulating them until they make up a whole day or month that is added later, so the calendar stays in step with the motion of the bodies. Without it errors would accumulate and the months and seasons would move away from their places.

Intercalating the month

The moon completes its cycle in about 29 days, 12 hours and 44 minutes, so the length of the month is not a whole number of days. So months alternate between 29 and 30 days: when a month ends at 29 days the remaining hours (about half a day) are kept, and over two or three cycles they accumulate into a whole day that is added to a month, making it 30 days. In this way the lunar calendar stays in step with the moon’s cycle without drifting. That is, we measure the month in days, and add a day when needed to correct the fraction.

Intercalating the year

The solar year is about 365 days and 6 hours, and if these hours are not counted the calendar gradually drifts from the solar cycle. So the leap year was devised: a day is added about every four years, making the year 366 days, as the extra hours accumulate (6 hours × 4 years = 24 hours = a whole day). This is what keeps solar calendars — such as the Gregorian and the Persian — in step with the seasons over the long term. That is, we measure the year in days, and add a day periodically to settle the fraction.

Intercalating the ‘ām

The ‘ām is the relation between the lunar months (12 months) and the solar year, and here a greater problem appears:

• The solar year ≈ 365 days.
• Twelve lunar months ≈ 354 days.

That is a difference of about 11 days every year. Left unaddressed, every lunar month would move through the seasons, so we find Ramadan in summer at one time and in winter at another, as in the Hijri calendar. So some calendars (such as the Hebrew and the Chinese) dealt with this difference by adding a whole lunar month every few years — called the “leap month” — so that the lunar years equal the solar years and the ‘ām stays in step with the seasons. That is, we measure the ‘ām in months, and add a month when needed to settle the large difference between moon and sun.

The ‘ām

It may be thought that a‘wām and sinīn (both rendered “years” in English) are the same, but there is an essential difference between them. The ‘ām is a hybrid unit of time arising from combining the lunar months with the solar year, representing the form that reconciles the moon and the sun together.

The sanah is a natural unit standing on its own (solar), and the month another natural unit (lunar), while the ‘ām does not exist without the intercalation that binds these independent units. So the ‘ām is the lunisolar calendar, in which the units of day, month and year interlock after the differences are adjusted. Whoever does not use the three units with intercalation has not entered into the reckoning of the ‘ām. Linguistically, ‘ām comes from “the more general and comprehensive,” i.e. broader than the sanah; hence the Qur’an distinguishes between sanah and ‘ām and does not use one in place of the other arbitrarily.

The difference between the ‘ām and the sanah

So the ‘ām is the “link” between the sun (expressed by the sanah) and the moon (expressed by the month), and it is the calendar that achieves balance between the two astronomical motions.

The ‘ām in ancient civilizations

Studies indicate that all civilizations — despite their different religions — used a form of lunisolar calendar, because it is the closest to human nature, combining the regularity of the sun with the visible changes of the moon. But time brought distortion into them; some nations abandoned the moon and kept only the sun, while keeping the division of the year into 12 months:

• The Gregorian calendar used today is Hebrew (lunisolar) in origin, but the Romans — when they imposed their control over Christianity and wanted to cut the link with the Jews — modified it and made it purely solar, abandoning the moon and keeping the sun.
• And some pagans did the opposite: they used the moon and abandoned the sun. The result is that every nation departed from the origin: the integrated lunisolar system.

The philosophical and rational dimension

One lesson of this chapter is that a person should not hand over their mind to others, whether to those called “religious scholars” or “worldly scholars”; anyone may go astray when the critical mind is absent. Many have fallen into the trap of shiny headlines such as “scientists have proved” or “scientifically established,” which later turned out to be temporary hypotheses. Hence we distinguish between:

• Experimental sciences: testable, but they may change as the data change.
• Fixed laws: such as mathematical laws, which do not change.

The seasons

The four seasons are not an arbitrary climatic division but a fixed, natural astronomical division resulting from the sun’s apparent motion between the tropics of Cancer and Capricorn. Their boundaries begin at the equinoxes and solstices, which are constants that do not change.

Spring begins at the spring equinox, when the sun is overhead at the equator heading north toward the Tropic of Cancer (about 93 days), and daytime gradually lengthens in the northern half. Then summer begins at the summer solstice, when the sun reaches its northernmost point on the Tropic of Cancer and turns back toward the equator (about 93 days), with the longest daytime and shortest night. Then autumn at the autumn equinox, when the sun is again overhead at the equator heading south toward the Tropic of Capricorn (about 90 days), and daytime and night become nearly equal. Then winter at the winter solstice, when the sun reaches its southernmost point on the Tropic of Capricorn (about 90 days), with the shortest daytime and longest night.

Astronomical versus climatic seasons

• Astronomical seasons: fixed, covering the whole earth, and defined by astronomical moments (the equinoxes and solstices).
• Climatic seasons: differ from country to country according to climate; some tropical regions divide the year into six seasons (rainy season, dry season…) instead of four.

At the equinoxes night and daytime are equal in both halves of the earth, and at the solstices the contrast is greatest (longest daytime and shortest night, or the reverse) — a system that ensures the vital balance on earth.

The ḥawl

The ḥawl is a cycle of time that begins from one of the seasons and returns to it, disregarding the details of months and days. Whoever is born in the middle of autumn, the beginning of the next autumn is a “ḥawl” for them — and it may be shorter or longer than the sanah. That is why the Qur’an distinguishes between the ḥawl, the sanah and the ‘ām, giving each its own meaning.

The ḥawl in the Qur’an

The word ḥawl occurs in the Qur’an in only two places, both tied to precise rulings:

1) The ḥawl in nursing:

Two verses that set the durations complement it:

• “and his weaning is in two ‘āms” [Luqman: 14]
• “and his bearing and weaning are thirty months” [Al-Ahqaf: 15]

The first sets a general period, the second shows the minimum (21 months if the pregnancy is 9 months, or 23 months if it is 7), and the third sets the maximum (two complete ḥawls ≈ 30 months).

2) The ḥawl in the waiting period of a widow:

Then the following verse gives the detail:

• “a fast of three days during the Hajj and of seven when you return; those are ten complete” [Al-Baqarah: 196] → i.e. seven days
• “And We appointed for Moses thirty nights and completed them with ten” [Al-A‘raf: 142] → i.e. ten nights
• “And they remained in their cave three hundred years and added nine” [Al-Kahf: 25] → i.e. nine years

By the same logic the verse “four months and ten” is understood as “fourteen months,” so the texts agree and the apparent contradiction disappears.

The ḥawl and the duration of pregnancy

God did not mention pregnancy in the waiting period of a widow — unlike that of a divorced woman — because the duration of the ḥawl (14 months) already includes the maximum duration of pregnancy (9 months):

The ḥawl between the sanah and the ‘ām

A common misunderstanding

Many researchers have confused the sanah, the ‘ām and the ḥawl, claiming that sanah denotes hardship and drought and ‘ām prosperity, citing the story of Joseph:

But reflection reveals that:

• “seven sinīn” = seven years of prosperity and farming.
• “seven hard ones” = seven years of drought, which are not described as sinīn.
• “an ‘ām” = the stage that follows the hardship, in which rain and fertility return.

So the difference between sanah, ‘ām and ḥawl is an objective terminological difference, not an arbitrary connotation.

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