I heard this on the radio the other day and just found a link to a site that has the info re: how the birth of Jesus was determined.....
"In the 6th Century, the Roman monk-mathematician-astronomer named Dionysis Exeguus (Dionysis the Little) reformed the calendar to pivot around the birth of Christ. He dated the Nativity 753 years from the founding of Rome, calculated to the date King Herod died. But Dionysis miscalculated, because Herod died only 749 years after the founding of Rome, thus 4BC.
Herod, who ordered all the babies in Bethlehem younger than 2 years killed, was, of course, alive when the Magi visited the baby Jesus. So we know that Jesus was born in or before 4BC, as astronomers point out when referring to the Star of Bethlehem.
The reference to the birth of Jesus "two thousand years ago" is wrong in two ways: a. there was no year 0, thus we have had only 1998 years since Dionysis (incorrectly) calculated the year of the Nativity. b. Dionysis's calculation was off by at least 5 years, as mentioned above.
In the year 274AD, solstice fell on 25th December, and Roman Emperor Aurelian proclaimed the date as "Natalis Solis Invicti," the festival of the birth of the invincible sun. In 320 AD, Pope Julius I specified the 25th of December as the official date of the birth of Jesus Christ. In 325AD, Constantine the Great, the first Christian Roman emperor, introduced Christmas as an immovable feast on 25 December. In 354AD, Bishop Liberius of Rome officially ordered his members to celebrate the birth of Jesus on 25 December.
In some parts of the Roman Empire (mostly the Eastern parts), solstice was celebrated on 6 January, the last festival day for those who started solstice on 25 December. (Saturnalia was held over 12 days.) The Orthodox Churches of Eastern Europe celebrate Christmas on 6 January. The most likely year that Jesus was born, is 6BC, probably in the month of March. There was no year 0 (zero) recorded, so the 2nd millennium celebration of the birth of Jesus should have been held in March 1995. But considering that Nativity was not celebrated at all for the first 300-or-so years, and that Christmas became widely popular only in the 19th Century, it remains remarkable that the birthday of Jesus Christ today is one of the biggest industries in the world. A rather apt acknowledgement."
Hope you found it interesting. Count your blessings and have a very Merry Christmas!