He determined to number the years from that battle, which took place in the Ist year of the 117th Olympiad. That year became Year 1 of the "Seleucid Era," and later years continued in succession as 2, 3, 4, 5, and so on. Nothing more elaborate than that.

The Seleucid Era was of unusual importance because Se leucus and his descendants ruled over Judea, which there fore adopted the system. Even after the Jews broke free o If the Seleucids under the leadership of the Maccabees, they continued to use the Seleucid Era in dating their com mercial transactions over the length and breadth of the ancient world. Those commercial records can be tied in with various local year-dating systems, so that many of them could be accurately synchronized as a result.

The most important year-dating system of the ancient world, however, was that of the "Roman Era." This began with the year in which Rome was founded. According to tradition, this was the 4th Year of the 6th Olympiad, which came to be considered as I A.U.C. (The abbrevia tion "A.U.C." stands for "Anno Urbis Conditae"; that is, "The Year of the Founding of the City.")

Using the Roman Era, the Battle of Zama, in which Hannibal was defeated, was fought in 553 A.U.C., while Julius Caesar was assassinated in 710 A.U.C., and so on. This system gradually spread over the ancient world, as Rome waxed supreme, and lasted well into early medieval times.

The early Christians, anxious to show that biblical records antedated those of Greece and Rome, strove to begin counting at a date earlier than that of either the founding of Rome or the beginning of the Olympian Games. A Church historian, Eusebius of Caesarea, who lived about 1050 A.U.C., calculated that the Patriarch, Abraham, bad been born 1263 years before the founding of Rome. Therefore he adopted that year as his Year 1, so that 1050 A.u.c. became 2313, Era of Abraham.

Once the Bible was thoroughly established as the book of the western world, it was possible to carry matters to their logical extreme and date the years from the creation of the world. The medieval Jews calculated that the crea tion of the world had taken place 3007 years before the founding of Rome, while various Christian calculators chose years varying from 3251 to 4755 years before the founding of Rome. These are the various "Mundane Eras" ("Eras of the World"). The Jewish Mundane Era is used today in the Jewish calendar, so that in September 1964, the Jewish year 5725 began.

The Mundane Eras have one important factor in their favor. They start early enough so that there are very few, if any, dates in recorded history that have to be given negative numbers. This is, not true of the Roman Era, for instance. The founding of the Olympian Games, the Trojan War, the reign of David, the building of the Pyramids, all came before the foundin of Rome and have to be given negative year numbers.

The Romans wouldn't have cared, of course, for none of the ancients were very chronology conscious, but modem historians would. In fact, modem historians are even worse off than they would have been if the Roman Era had been retained.

About 1288 A.U.c., a Syrian monk named Dionysius Exiguus, working from biblical data and secular records, calculated that Jesus must have been born in 754 A.U.C.

This seemed a good time to use as a beginning for counting the years, and in the time of Charlemagne (two and a half centuries after Dionysius) this notion won out.

The year 754 A.U.c. became A.1). I (standing for Anno Domini, meaning "the year of the Lord"). By this new "Christian Era," the founding of Rome took place in 753 B.C. ("before Christ"). The first year of the first Olvmt)iad was in 776 B.C., the first year of the Seleucid Era was in 312 Bc., and so on.

This is the system used today, and means that all or ancient history from Sumer to Augustus must be dated in negative numbers, and we must forever remember that Caesar was assassinated in 44 B.C. and that the next year is number 43 and not 45.

Worse still, Dionysius was wrong in his calculations.

Matthew 2: 1 clearly states that "Jesus was born in Bethle hem of Judea in the days of Herod the king." This Herod is the so-called Herod the Great, who was born about 681 A.u.c., and was made king of Judea by Mark Antony in 714 A.u.c. He died (and this is known as certainly as any ancient date is known) in 750 A.U.c., and therefore Jesus could not have been born any later than 750 A.U.C.

But 750 A.U.c., according to the system of Dio'nysius Exiguus, is 4 B.C., and therefore you constantly find in lists of dates that Jesus was born in 4 B.C.; that is, four years before the birth of Jesus.

In fact, there is no reason to be sure that Jesus was born in the very year that Herod died. In Matthew 2:16, it is written that Herod, in an attempt to kill Jesus, ordered all male children of two years and under to be slain. This verse can be interpreted as indicating that Jesus may have been at least two years old while Herod was still alive, and might therefore have been born as early as 6 B.C. Indeed, some estimates have placed the birth of Jesus as early as 17 B.C. 

Which forces me to admit sadly that although I lo begin at the beginning, I can't always be sure where beginning is.

My son is bearing, with strained patience, the quasi-hu morous changes being rung upon his last name by his grade,school classmates. My explanation to him that the name "Asimov," properly pronounced, has a noble reso nance like the distant clash of sword on shield in the age of chivalry, leaves him unmoved. The hostile look in his eyes tells me quite plainly that he considers it my duty as a father to change my name to "Smith" forthwith.

Of course, I sympathize with him, for in my time, 1, too, have been victimized in this fashion. The ordinary misspellings of the uninformed I lay to one side. However, there was one time…

It was when I was in the Army and working out my stint in basic training. One of the courses to which we were exposed was map-reading, which had the great advantage of being better than drilling and hiking. And then, like a bolt of lightning, the sergeant in charge pronounced the fatal word "azimuth" and all faces turned toward me.

I stared back at those stalwart soldier-boys in horror, for I realized that behind every pair of beady little eyes, a small brain had suddenly discovered a source of infinite fun.

You're right. For what seemed months, I was Isaac Azimuth to every comic on the post, and every soldier on the post considered himself a comic. But, as I told myself (paraphrasing a great American poet), "This is the army, Mr. Azimuth."

Somehow, I survived.

And, as fitting revenge, what better than to tell all you inoffensive Gentle Readers, in full and leisurely detail, exactly what azimuth is? 

It all starts with direction. The first, most primitive, and most useful way of indicating direction is to point. "They went that-a-way." Or, you can make use of some land mark known to one and all, "Let's head them off at the gulch.

This is all right if you are concerned with a small sec tion of the Earth's surface; one with which you and your friends are intimately familiar. Once the horizons widen, however, there is a search for methods of giving directions that do not depend in any way on local terrain, but are the same everywhere on the Earth.

An obvious method is to make use of the direction of the rising Sun and that of the setting Sun. (These direc tions change from day to day, but you can take the average over the period of a year.) These are opposite directions, of course, which we call "east" and "west." Another pair of opposites can be set up perpendicular to these and be called "north" and "south."

If, at any place, north, east, south, and west are deter mined (and this could be done accurately enough, even in prehistoric times, by careful observations of the Sun) there is nothing, in principle, to prevent still finer directions from being established. We can have northeast, north northeast, northeast by north, and so on.

With a compass you can accept directions of this sort, follow them for specified distances or via specified land marks, and go wherever you are told to go. Furthermore, if you want to map the Earth, you can start at some point, travel a known distance in a known direction to another point, and locate that point (to scale) on the map. You can then do the same for a third point, and a fourth, and a fifth, and so on. In principle the entire surface of the planet can be laid out in this manner, as accurately as you wish, upon a globe.

However, the fact that a thing can be done "in prin ciple" is cold comfort if it is unbearably tedious and would take a million men a million years. Besides, the compass was unknown to western man until the thirteenth century, and the Greek geographers, in trying to map the world, had to use other dodges.

One method was to note the position of the Sun at mid day; that is at the moment just halfway between sunrise and sunset. On any particular day there will be some spots on Earth where the Sun will be directly overhead at mid day. The ancient Greeks knew this to be true of southern Egypt in late June, for instance. In Europe, however, the sun at midday always fell short of the overhead point.

This could easily be explained once it was realized that the Earth was a sphere. It could furthermore be shown, without difficulty that all points on Earth at which the Sun, on some particular day, fell equally short of the overhead point at midday, were on a single east-west line. Such a line could be drawn on the map and used as a reference for the location of other points. The first to do so was a Greek geographer named Dicaearchus, who lived about 300 B.c. and was one of Aristotle s pupils.

Such a line is called a line of "latitude," from a Latin word meaning broad or wide, for when making use of the usual convention of putting north at the top of a map, the east-west lines run in the direction of its width.

Naturally, a number of different lines of latitude can be determined. All run east-west and all circle the sphere of the Earth at constant distances from each other, and so are parallel. They are therefore referred to as "parallels of latitude."

The nearer the parallels of latitude to either pole, the smaller the circles they make. (If you have a globe, look at it and see.) The longest parallel is equidistant from the poles and makes the largest circle, taking in the maximum girth of the Earth. Since it divides the Earth into two equal halves, north and south, it is called the "equator" (from a Latin word meaning "equalizer").