Important Dates in the Lives of Jesus and Mary 

his place among the gods. For this reason, ancient coins and images of Julius Caesar often show a comet 

above his head. 

    How can modern astronomy determine which comets appeared when in ancient times? For the most part, it 

cannot; however, independent verification of comet sightings is provided by ancient Chinese and Korean 

astronomers, who observed the stars closely and kept careful records of the date and location of comets. Since 

the ancient Chinese calendar system (a lunar calendar) is unrelated to the 

B.C.

/

A.D.

 system, this provides a 

way to verify the sightings mentioned by the Roman historians. 

    The best modern source for information on these ancient comet sightings is undoubtedly  Cometography, A 

Catalog of Comets, Volume 1, by Gary W. Kronk. This book covers every ancient comet from 675 

B.C.

 to 

A.D.

1799, and consolidates all of the often quoted sources for ancient comet data, such as the  Hou Han shu (an 

ancient Chinese text), J. Williams, Ho Peng Yoke, A. G. Pingre, and others. Treatment is even given to brief 

mentions of comets found in ancient Roman texts. 

    Comets are typically visible (with the naked eye) for a period of a few days or weeks to, at most, several 

months. They travel in an arc around the sun and should be visible, at some point in their path, from both 

Europe and China. Thus, any noted comet in Roman history would likely have been observed and mentioned 

by the ancient astronomers of China. It should then be possible, in a given chronology for dates in the reigns of 

Roman emperors, to match the mention of comets in Roman texts to those in Chinese texts. Comet data is 

examined in chapter 13 of this book, along with a revised chronology of the reigns of the Roman emperors in 

the first century 

A.D.

Scholars Are Uncertain 

    In 525 

A.D.

, Pope St. John I, asked a Roman Catholic abbot named Dionysius Exiguus to determine the 

dates of Easter for future years. Dionysius was a well known theologian, who also excelled at mathematics 

and astronomy. The date for Easter is determined by astronomy.

14

 In determining these dates, Dionysius 

objected to the then current system of numbering the years from the time of the emperor Diocletian, (third 

century 

A.D.

), under whose reign there was a great persecution of Christians.

15

 Instead, he devised a calendar 

system where the years are numbered according to the Incarnation of Jesus Christ, ab incarnatione Domini 

(`from the Incarnation of the Lord').

16

 Today, we use the abbreviation  

A.D.

,  which stands for Anno Domini 

(`in the year of the Lord'), but the numbering of the years is according to Dionysius.

17

    Dionysius numbered the first full year after the Incarnation and Birth of Christ as 

A.D.

 1. Thus, in 

A.D.

 1, 

according to Dionysius, Christ would have completed one year of life since the Incarnation (early in the 

calendar year), and one year of life since His Holy Birth (late in the calendar year). The number of the year 

should reflect the age of Christ in this system. The custom of referring to the years before 

A.D.

 1 as  

B.C.

(`before Christ') did not develop until a later time. However, Dionysius did believe that Christ was born in the 

year before 

A.D.

 1, which we now call 1 

B.C.

    Even though this new system of numbering the years was accepted by the Church, and by much of society, 

there is today no agreement among historians, Biblical scholars, theologians, or Church leaders that Dionysius 

chose the correct year to call 

A.D.

 1. In other words, there is no general agreement that Christ was born in 1 

B.C.

 It is not the official teaching of the Catholic Church, nor of any other Christian Church of which I am 

aware, that Jesus Christ was necessarily born in 1 

B.C.

, as was the opinion of Dionysius. 

    Since hundreds of years had passed between the Birth of Christ and the time of Dionysius, he could well 

have been mistaken about which year was the year of Christ's Birth. Also, he numbered the years as his 

reference point using the Roman dating system A.U.C.,  ab urbe condita, (from the founding of the city of 

Rome). So, any errors in the Roman system of dating the years would have affected his determination as to in 

which year Christ was born. As we shall see in chapter 13 of this book, Dionysius would have been correct as 

to the year of Christ's Birth, except for some errors in the Roman histories upon which Dionysius depended. 

The Teaching of the Church 

    The Catholic Church has no official teaching as to the year of the Birth or Crucifixion of Jesus Christ. And, 

even though we celebrate the Birth of Jesus Christ on December 25, the Church does not teach that this was 

16