Hence the year 2000 will be celebrated as the Great Jubilee. Most scholars today suppose Jesus was born at least 4 years Before Christ. But even if we ignore the fine points of actual chronology, and take the year 2000 as symbolic for the 2,000th year of the Christ, it is still not the 2,000th anniversary of his birth. But there was no year zero. The early sequence of years goes from 1 BC immediately to AD 1.
Astronomers nevertheless use a zero-year for some of their calculations.
Their counting device replaces AD years with positive numbers, and years BC with negative numbers. Converting to a number line in this way, they feel compelled to recognize a zero-point between the negative and positive numbers. It is too easy to ridicule someone, especially a church, for imperfect counting. It is more interesting to recognize that people attach greater significance to numerical landmarks in time, like the year 2000, than to actual chronology. To us, AD 2000 means the beginning of a new century, a new millennium, and a special anniversary of the birth of Christ.