How to Convert Years

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HOW TO CONVERT YEARS BETWEEN THE MUSLIM AND COMMON CALENDARS The conversion process is simple if all we need to do is find the approximate year. The year of the prophet s migration, the hijra, is counted as year one in the Muslim calendar. This year corresponds to year 622 C.E. of the Gregorian Calendar. There is no year zero. But we may imagine a Year Zero for our calculations. Year Zero would be 621 C.E. From this it is immediately evident that the Gregorian calendar is ahead by 621 years. Hence if we were given, for example, the year 622 C.E. asked to find the equivalent year in the Hijri calendar, we would simply subtract 621 from 622 and arrive at 1. The reverse procedure would be followed to convert from a Muslim calendar year to the Gregorian year. We would simply add 621 to the hijri year to arrive at the equivalent year C.E. The procedure is only slightly more complicated when we wish to convert years that are further away from the hijra, for then we need to adjust for the different lengths of the years on the two systems. The Common Era Calendar consists of 365 days, except for leap years, a reckoning that coincides with one earth rotation around the sun. We may call this, for our convenience here, a solar year. The Muslim calendar, though consisting also of 12 months, comprises only 354 days on average, as the months follow the lunar cycle which varies between 29 and 30 days each. We may call this a lunar year. It follows that the lunar year is 11 days shorter than a solar year. Hence if the two years were perfectly aligned from the start, the lunar year would finish 11 days before the end of the solar year. After 33 solar years, 34 lunar years will have elapsed (since 11 days x 33 solar years = 363 days). This many days is more than the length of a lunar year, but since we are dealing with approximations anyway, it will work for our purpose here. In conclusion, as we deal with years further from the hijra we would have to adjust one year for approximately every 33 years; or three years for every hundred. Now, for a real-life example, let s say we are dealing with the date of al-Ghazali s death, which we know to be 1111 C.E. To find the hijri date we need to do two things: First, we need to find out how many solar years this has been since Year Zero. This is done by the simplest method described above: we subtract 621 from 1111 and arrive at 490 solar years since Year Zero. Second, we need to find out the equivalent number of lunar years. We know that a hundred solar years is equal to 103 lunar years. If we had a calculator handy we would simply multiply 490 by 1.03 to arrive at the number of lunar years. But we can estimate the result without a calculator. We need to add 3 lunar years for every 100 solar years, or one lunar year for every 33 solar years. So we need to ask how many hundreds are in 490, and how many 33s in what is left over of that number. There are obviously 4 hundreds and much more than two 33s. But since we need only find the approximate date we may treat 490 as we would 500. Hence we need to add 15 lunar years (5 x 3). Since 490 solar years elapsed between Year Zero and the death of al-Ghazali, we conclude that 490 + 15 = 505 lunar years elapsed since Year Zero. Hence al-Ghazali died in the year 505 H. We may now do this in reverse for the exercise. Given that al-Ghazali died in 505 H, we can compute the C.E. year of his death. We already know that this is 505 lunar years since Year Zero. We need to know how many solar years have elapsed since Year Zero. To find this, we need to subtract

three years for every 103 years (since 103 lunar years = 100 solar years). Now 505 is approximately 5 x 103. Hence we need to subtract 5 x 3 = 15 years from 505. Hence al-Ghazali died 505 15 = 490 solar years since Year Zero. We now need to add 490 to Year Zero, which is the year 621 C.E. This gives us the year of his death on the Gregorian calendar. Hence he died in the year 1111 (this being equal to 490 + 621). Now let s do it for Ibn Taymiya. He died in 1328 C.E. To find the hijri date we first subtract 621. The result is 707. This first step gives us the number of solar years since Year Zero. To find the year on the Hijri calendar, we need to add three years for every hundred. Since there are seven hundred years approximately, we would add 7 x 3 = 21. Hence 707 + 21 = 728 years have elapsed since our putative Year Zero. Ibn Taymiya died in 728 H. We can do it in reverse. Given that he died in 728 H, in what year of the Gregorian calendar did he die? First step: We know from the hijri date that 728 lunar years have elapsed since the hijra (or, more accurately, since Year Zero). To find out how many solar years have elapsed since the hijra we deduct three years for every 103. Now, 7 x 103 = 721. That is close enough to 728. So we need to subtract 7 x 3 = 21 years from the number of lunar years to arrive at the number of solar years. Hence 728 21 = 707 solar years have elapsed since Year Zero. Second step: Recall that Year Zero is 621 on the Gregorian calendar. Since 707 solar years have elapsed between Year Zero and Ibn Taymiya s death, Ibn Taymiya died in the year 1328 (this being equal to 621 + 707) of the Gregorian calendar. The above explanation tries to capture the logic behind what we may now reduce to a simple formula. To go from C.E. to Hijri, take away 621 and add back 3 years for every 100. To go from Hijri to C.E., add 621 and take back 3 years for every 103.

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