That Wintry Night

As explained here: 

Note on the date of Christmas, from 30 Days, an Italian Catholic publication:

"December 25 is an historical date," Professor Tommaso Federici, Professor at the Pontifical Urbanian University and a consultant to two Vatican Congregations, has stressed.

In an article in the Osservatore Romano on December 24, he wrote: "December 25 is explained as the 'Christianization' of a pagan feast, 'birth of the Sol Invictus'; or as the symmetrical balance, an aesthetic balance between the winter solstice (Dec. 21-22) and the spring equinox (March 23-24).

But a discovery of recent years has shed definitive light on the date of the Lord's birth. As long ago as 1958, the Israeli scholar Shemaryahu Talmon published an in-depth study on the calendar of the Qumran sect [Ed. based , in part, on Parchment Number 321 -- 4 Q 321 -- of the Qumran Dead Sea Scrolls, see picture at left], and he reconstructed without the shadow of doubt the order of the sacerdotal rota system for the temple of Jerusalem (1 Paralipomenon/Chronicles 24, 7-18) in New Testament times.

Here the family of Abijah, of which Zechariah  (Zachary) was a descendant, father of John the herald and forerunner (Luke 1, 5), was required to officiate twice a year, on the days 8-14 of the third month, and on the days 24-30 of the eighth month.

This latter period fell at about the end of September. It is not without reason that the Byzantine calendar celebrated 'John's conception' on September 23 and his birth nine months later, on June 24. The 'six months' after the Annunciation established as a liturgical feast on March 25, comes three months before the forerunner's birth, prelude to the nine months in December: December 25 is a date of history."

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In other words, according to the evidence of the Dead Sea Scrolls and Sacred Scripture, our liturgical calendar is accurate:
 

end of September	Zachary (Zechariah) "executed his priestly function" (Luke 1:8) according to his class. His wife, Elizabeth, conceived (the Church traditionally holds St. John's conception to have taken place on 23 September) just as St. Gabriel said (Luke 1:24) and hid herself away for 5 months.
25 March, the Feast of the Annunciation	In the sixth month of Elizabeth's pregnancy (Luke 1:26), St. Gabriel appears to Mary to tell her she is to have a child
24 June, the Feast of St. John the Baptist	Three months after the Annunciation, St. John the Baptist was born, at a time when the days were becoming shorter
25 December	Nine months after the Annunciation, Jesus was born, at a time when the days were becoming longer.

In addition to this, the ancient "integral age" tradition is that the Prophets died on the same day they were conceived. With Passover set at 25 March, the Annunciation would have taken place on that same date -- and the Nativity would've taken place 9 months later, on 25 December.

To rebut the idea that Jesus had to have been born (rather than conceived) in the Spring because the shepherds were in their fields, which wouldn't have been so in the Winter, there's this, from the Anglican scholar, Alfred Edersheim, in his "The Life and Times of Jesus The Messiah":

And yet Jewish tradition may here prove both illustrative and helpful. That the Messiah was to be born in Bethlehem, was a settled conviction. Equally so, was the belief , that He was to be revealed from Migdal Eder, 'the tower of the flock.'

This Migdal Eder was not the watchtower for the ordinary flocks which pastured on the barren sheepground beyond Bethlehem, but lay close to the town, on the road to Jerusalem.

A passage in the Mishnah [951] leads to the conclusion, that the flocks, which pastured there, were destined for Temple-sacrifices [952], and, accordingly, that the shepherds, who watched over them, were not ordinary shepherds.

The latter were under the ban of Rabbinism, on account of their necessary isolation from religious ordinances, and their manner of life, which rendered strict legal observance unlikely, if not absolutely impossible.

The same Mishnaic passage also leads us to infer, that these flocks lay out all the year round, since they are spoken of as in the fields thirty days before the Passover -- that is, in the month of February, when in Palestine the average rainfall is nearly greatest.

Thus, Jewish tradition in some dim manner apprehended the first revelation of the Messiah from that Migdal Eder, where shepherds watched the Temple-flocks all the year round. Of the deep symbolic significance of such a coincidence, it is needless to speak.

It was, then, on that ‘wintry night’ of the 25th of December, that shepherds watched the flocks destined for sacrificial services, in the very place consecrated by tradition as that where the Messiah was to be first revealed.

Of a sudden came the long-delayed, unthought-of announcement.