General Hugues de Nanteuil makes a compelling case in his book,
The Dates of the Birth and Death of Jesus Christ that the traditional dates used by the Church, i.e., that Jesus was actually born on December 25th 1 B.C. and that he was circuмcised on January 1, A.D. 1 (eight days after his birth) are the actual dates of the historical events.
The book can be obtained from Tradibooks, available online at:
http://stores.lulu.com/tradibooksThus, the actual birthday of the Church is indeed on Pentecost Sunday in the year A.D. 33. Those who claim otherwise do not have evidence that another date is correct; they merely question the evidence (needlessly, in my opinion) that the dates always accepted by the Church are incorrect.